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kmemcheck: rip it out

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Fix up makefiles, remove references, and git rm kmemcheck.

Link: http://lkml.kernel.org/r/20171007030159.22241-4-alexander.levin@verizon.com
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vegard Nossum <vegardno@ifi.uio.no>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Tim Hansen <devtimhansen@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Levin, Alexander (Sasha Levin) 2017-11-15 17:36:02 -08:00 committed by Linus Torvalds
parent d8be75663c
commit 4675ff05de
35 changed files with 7 additions and 2592 deletions
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7
Documentation/admin-guide/kernel-parameters.txt
View file

@ -1864,13 +1864,6 @@
Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
the default is off. the default is off.
kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
Valid arguments: 0, 1, 2
kmemcheck=0 (disabled)
kmemcheck=1 (enabled)
kmemcheck=2 (one-shot mode)
Default: 2 (one-shot mode)
kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
Default is 0 (don't ignore, but inject #GP) Default is 0 (don't ignore, but inject #GP)

1
Documentation/dev-tools/index.rst
View file

@ -21,7 +21,6 @@ whole; patches welcome!
kasan kasan
ubsan ubsan
kmemleak kmemleak
kmemcheck
gdb-kernel-debugging gdb-kernel-debugging
kgdb kgdb
kselftest kselftest

733
Documentation/dev-tools/kmemcheck.rst
View file

@ -1,733 +0,0 @@
Getting started with kmemcheck
==============================
Vegard Nossum <vegardno@ifi.uio.no>
Introduction
------------
kmemcheck is a debugging feature for the Linux Kernel. More specifically, it
is a dynamic checker that detects and warns about some uses of uninitialized
memory.
Userspace programmers might be familiar with Valgrind's memcheck. The main
difference between memcheck and kmemcheck is that memcheck works for userspace
programs only, and kmemcheck works for the kernel only. The implementations
are of course vastly different. Because of this, kmemcheck is not as accurate
as memcheck, but it turns out to be good enough in practice to discover real
programmer errors that the compiler is not able to find through static
analysis.
Enabling kmemcheck on a kernel will probably slow it down to the extent that
the machine will not be usable for normal workloads such as e.g. an
interactive desktop. kmemcheck will also cause the kernel to use about twice
as much memory as normal. For this reason, kmemcheck is strictly a debugging
feature.
Downloading
-----------
As of version 2.6.31-rc1, kmemcheck is included in the mainline kernel.
Configuring and compiling
-------------------------
kmemcheck only works for the x86 (both 32- and 64-bit) platform. A number of
configuration variables must have specific settings in order for the kmemcheck
menu to even appear in "menuconfig". These are:
- ``CONFIG_CC_OPTIMIZE_FOR_SIZE=n``
This option is located under "General setup" / "Optimize for size".
Without this, gcc will use certain optimizations that usually lead to
false positive warnings from kmemcheck. An example of this is a 16-bit
field in a struct, where gcc may load 32 bits, then discard the upper
16 bits. kmemcheck sees only the 32-bit load, and may trigger a
warning for the upper 16 bits (if they're uninitialized).
- ``CONFIG_SLAB=y`` or ``CONFIG_SLUB=y``
This option is located under "General setup" / "Choose SLAB
allocator".
- ``CONFIG_FUNCTION_TRACER=n``
This option is located under "Kernel hacking" / "Tracers" / "Kernel
Function Tracer"
When function tracing is compiled in, gcc emits a call to another
function at the beginning of every function. This means that when the
page fault handler is called, the ftrace framework will be called
before kmemcheck has had a chance to handle the fault. If ftrace then
modifies memory that was tracked by kmemcheck, the result is an
endless recursive page fault.
- ``CONFIG_DEBUG_PAGEALLOC=n``
This option is located under "Kernel hacking" / "Memory Debugging"
/ "Debug page memory allocations".
In addition, I highly recommend turning on ``CONFIG_DEBUG_INFO=y``. This is also
located under "Kernel hacking". With this, you will be able to get line number
information from the kmemcheck warnings, which is extremely valuable in
debugging a problem. This option is not mandatory, however, because it slows
down the compilation process and produces a much bigger kernel image.
Now the kmemcheck menu should be visible (under "Kernel hacking" / "Memory
Debugging" / "kmemcheck: trap use of uninitialized memory"). Here follows
a description of the kmemcheck configuration variables:
- ``CONFIG_KMEMCHECK``
This must be enabled in order to use kmemcheck at all...
- ``CONFIG_KMEMCHECK_``[``DISABLED`` | ``ENABLED`` | ``ONESHOT``]``_BY_DEFAULT``
This option controls the status of kmemcheck at boot-time. "Enabled"
will enable kmemcheck right from the start, "disabled" will boot the
kernel as normal (but with the kmemcheck code compiled in, so it can
be enabled at run-time after the kernel has booted), and "one-shot" is
a special mode which will turn kmemcheck off automatically after
detecting the first use of uninitialized memory.
If you are using kmemcheck to actively debug a problem, then you
probably want to choose "enabled" here.
The one-shot mode is mostly useful in automated test setups because it
can prevent floods of warnings and increase the chances of the machine
surviving in case something is really wrong. In other cases, the one-
shot mode could actually be counter-productive because it would turn
itself off at the very first error -- in the case of a false positive
too -- and this would come in the way of debugging the specific
problem you were interested in.
If you would like to use your kernel as normal, but with a chance to
enable kmemcheck in case of some problem, it might be a good idea to
choose "disabled" here. When kmemcheck is disabled, most of the run-
time overhead is not incurred, and the kernel will be almost as fast
as normal.
- ``CONFIG_KMEMCHECK_QUEUE_SIZE``
Select the maximum number of error reports to store in an internal
(fixed-size) buffer. Since errors can occur virtually anywhere and in
any context, we need a temporary storage area which is guaranteed not
to generate any other page faults when accessed. The queue will be
emptied as soon as a tasklet may be scheduled. If the queue is full,
new error reports will be lost.
The default value of 64 is probably fine. If some code produces more
than 64 errors within an irqs-off section, then the code is likely to
produce many, many more, too, and these additional reports seldom give
any more information (the first report is usually the most valuable
anyway).
This number might have to be adjusted if you are not using serial
console or similar to capture the kernel log. If you are using the
"dmesg" command to save the log, then getting a lot of kmemcheck
warnings might overflow the kernel log itself, and the earlier reports
will get lost in that way instead. Try setting this to 10 or so on
such a setup.
- ``CONFIG_KMEMCHECK_SHADOW_COPY_SHIFT``
Select the number of shadow bytes to save along with each entry of the
error-report queue. These bytes indicate what parts of an allocation
are initialized, uninitialized, etc. and will be displayed when an
error is detected to help the debugging of a particular problem.
The number entered here is actually the logarithm of the number of
bytes that will be saved. So if you pick for example 5 here, kmemcheck
will save 2^5 = 32 bytes.
The default value should be fine for debugging most problems. It also
fits nicely within 80 columns.
- ``CONFIG_KMEMCHECK_PARTIAL_OK``
This option (when enabled) works around certain GCC optimizations that
produce 32-bit reads from 16-bit variables where the upper 16 bits are
thrown away afterwards.
The default value (enabled) is recommended. This may of course hide
some real errors, but disabling it would probably produce a lot of
false positives.
- ``CONFIG_KMEMCHECK_BITOPS_OK``
This option silences warnings that would be generated for bit-field
accesses where not all the bits are initialized at the same time. This
may also hide some real bugs.
This option is probably obsolete, or it should be replaced with
the kmemcheck-/bitfield-annotations for the code in question. The
default value is therefore fine.
Now compile the kernel as usual.
How to use
----------
Booting
~~~~~~~
First some information about the command-line options. There is only one
option specific to kmemcheck, and this is called "kmemcheck". It can be used
to override the default mode as chosen by the ``CONFIG_KMEMCHECK_*_BY_DEFAULT``
option. Its possible settings are:
- ``kmemcheck=0`` (disabled)
- ``kmemcheck=1`` (enabled)
- ``kmemcheck=2`` (one-shot mode)
If SLUB debugging has been enabled in the kernel, it may take precedence over
kmemcheck in such a way that the slab caches which are under SLUB debugging
will not be tracked by kmemcheck. In order to ensure that this doesn't happen
(even though it shouldn't by default), use SLUB's boot option ``slub_debug``,
like this: ``slub_debug=-``
In fact, this option may also be used for fine-grained control over SLUB vs.
kmemcheck. For example, if the command line includes
``kmemcheck=1 slub_debug=,dentry``, then SLUB debugging will be used only
for the "dentry" slab cache, and with kmemcheck tracking all the other
caches. This is advanced usage, however, and is not generally recommended.
Run-time enable/disable
~~~~~~~~~~~~~~~~~~~~~~~
When the kernel has booted, it is possible to enable or disable kmemcheck at
run-time. WARNING: This feature is still experimental and may cause false
positive warnings to appear. Therefore, try not to use this. If you find that
it doesn't work properly (e.g. you see an unreasonable amount of warnings), I
will be happy to take bug reports.
Use the file ``/proc/sys/kernel/kmemcheck`` for this purpose, e.g.::
$ echo 0 > /proc/sys/kernel/kmemcheck # disables kmemcheck
The numbers are the same as for the ``kmemcheck=`` command-line option.
Debugging
~~~~~~~~~
A typical report will look something like this::
WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (ffff88003e4a2024)
80000000000000000000000000000000000000000088ffff0000000000000000
i i i i u u u u i i i i i i i i u u u u u u u u u u u u u u u u
^
Pid: 1856, comm: ntpdate Not tainted 2.6.29-rc5 #264 945P-A
RIP: 0010:[<ffffffff8104ede8>] [<ffffffff8104ede8>] __dequeue_signal+0xc8/0x190
RSP: 0018:ffff88003cdf7d98 EFLAGS: 00210002
RAX: 0000000000000030 RBX: ffff88003d4ea968 RCX: 0000000000000009
RDX: ffff88003e5d6018 RSI: ffff88003e5d6024 RDI: ffff88003cdf7e84
RBP: ffff88003cdf7db8 R08: ffff88003e5d6000 R09: 0000000000000000
R10: 0000000000000080 R11: 0000000000000000 R12: 000000000000000e
R13: ffff88003cdf7e78 R14: ffff88003d530710 R15: ffff88003d5a98c8
FS: 0000000000000000(0000) GS:ffff880001982000(0063) knlGS:00000
CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: ffff88003f806ea0 CR3: 000000003c036000 CR4: 00000000000006a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff4ff0 DR7: 0000000000000400
[<ffffffff8104f04e>] dequeue_signal+0x8e/0x170
[<ffffffff81050bd8>] get_signal_to_deliver+0x98/0x390
[<ffffffff8100b87d>] do_notify_resume+0xad/0x7d0
[<ffffffff8100c7b5>] int_signal+0x12/0x17
[<ffffffffffffffff>] 0xffffffffffffffff
The single most valuable information in this report is the RIP (or EIP on 32-
bit) value. This will help us pinpoint exactly which instruction that caused
the warning.
If your kernel was compiled with ``CONFIG_DEBUG_INFO=y``, then all we have to do
is give this address to the addr2line program, like this::
$ addr2line -e vmlinux -i ffffffff8104ede8
arch/x86/include/asm/string_64.h:12
include/asm-generic/siginfo.h:287
kernel/signal.c:380
kernel/signal.c:410
The "``-e vmlinux``" tells addr2line which file to look in. **IMPORTANT:**
This must be the vmlinux of the kernel that produced the warning in the
first place! If not, the line number information will almost certainly be
wrong.
The "``-i``" tells addr2line to also print the line numbers of inlined
functions. In this case, the flag was very important, because otherwise,
it would only have printed the first line, which is just a call to
``memcpy()``, which could be called from a thousand places in the kernel, and
is therefore not very useful. These inlined functions would not show up in
the stack trace above, simply because the kernel doesn't load the extra
debugging information. This technique can of course be used with ordinary
kernel oopses as well.
In this case, it's the caller of ``memcpy()`` that is interesting, and it can be
found in ``include/asm-generic/siginfo.h``, line 287::
281 static inline void copy_siginfo(struct siginfo *to, struct siginfo *from)
282 {
283 if (from->si_code < 0)
284 memcpy(to, from, sizeof(*to));
285 else
286 /* _sigchld is currently the largest know union member */
287 memcpy(to, from, __ARCH_SI_PREAMBLE_SIZE + sizeof(from->_sifields._sigchld));
288 }
Since this was a read (kmemcheck usually warns about reads only, though it can
warn about writes to unallocated or freed memory as well), it was probably the
"from" argument which contained some uninitialized bytes. Following the chain
of calls, we move upwards to see where "from" was allocated or initialized,
``kernel/signal.c``, line 380::
359 static void collect_signal(int sig, struct sigpending *list, siginfo_t *info)
360 {
...
367 list_for_each_entry(q, &list->list, list) {
368 if (q->info.si_signo == sig) {
369 if (first)
370 goto still_pending;
371 first = q;
...
377 if (first) {
378 still_pending:
379 list_del_init(&first->list);
380 copy_siginfo(info, &first->info);
381 __sigqueue_free(first);
...
392 }
393 }
Here, it is ``&first->info`` that is being passed on to ``copy_siginfo()``. The
variable ``first`` was found on a list -- passed in as the second argument to
``collect_signal()``. We continue our journey through the stack, to figure out
where the item on "list" was allocated or initialized. We move to line 410::
395 static int __dequeue_signal(struct sigpending *pending, sigset_t *mask,
396 siginfo_t *info)
397 {
...
410 collect_signal(sig, pending, info);
...
414 }
Now we need to follow the ``pending`` pointer, since that is being passed on to
``collect_signal()`` as ``list``. At this point, we've run out of lines from the
"addr2line" output. Not to worry, we just paste the next addresses from the
kmemcheck stack dump, i.e.::
[<ffffffff8104f04e>] dequeue_signal+0x8e/0x170
[<ffffffff81050bd8>] get_signal_to_deliver+0x98/0x390
[<ffffffff8100b87d>] do_notify_resume+0xad/0x7d0
[<ffffffff8100c7b5>] int_signal+0x12/0x17
$ addr2line -e vmlinux -i ffffffff8104f04e ffffffff81050bd8 \
ffffffff8100b87d ffffffff8100c7b5
kernel/signal.c:446
kernel/signal.c:1806
arch/x86/kernel/signal.c:805
arch/x86/kernel/signal.c:871
arch/x86/kernel/entry_64.S:694
Remember that since these addresses were found on the stack and not as the
RIP value, they actually point to the _next_ instruction (they are return
addresses). This becomes obvious when we look at the code for line 446::
422 int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
423 {
...
431 signr = __dequeue_signal(&tsk->signal->shared_pending,
432 mask, info);
433 /*
434 * itimer signal ?
435 *
436 * itimers are process shared and we restart periodic
437 * itimers in the signal delivery path to prevent DoS
438 * attacks in the high resolution timer case. This is
439 * compliant with the old way of self restarting
440 * itimers, as the SIGALRM is a legacy signal and only
441 * queued once. Changing the restart behaviour to
442 * restart the timer in the signal dequeue path is
443 * reducing the timer noise on heavy loaded !highres
444 * systems too.
445 */
446 if (unlikely(signr == SIGALRM)) {
...
489 }
So instead of looking at 446, we should be looking at 431, which is the line
that executes just before 446. Here we see that what we are looking for is
``&tsk->signal->shared_pending``.
Our next task is now to figure out which function that puts items on this
``shared_pending`` list. A crude, but efficient tool, is ``git grep``::
$ git grep -n 'shared_pending' kernel/
...
kernel/signal.c:828: pending = group ? &t->signal->shared_pending : &t->pending;
kernel/signal.c:1339: pending = group ? &t->signal->shared_pending : &t->pending;
...
There were more results, but none of them were related to list operations,
and these were the only assignments. We inspect the line numbers more closely
and find that this is indeed where items are being added to the list::
816 static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
817 int group)
818 {
...
828 pending = group ? &t->signal->shared_pending : &t->pending;
...
851 q = __sigqueue_alloc(t, GFP_ATOMIC, (sig < SIGRTMIN &&
852 (is_si_special(info) ||
853 info->si_code >= 0)));
854 if (q) {
855 list_add_tail(&q->list, &pending->list);
...
890 }
and::
1309 int send_sigqueue(struct sigqueue *q, struct task_struct *t, int group)
1310 {
....
1339 pending = group ? &t->signal->shared_pending : &t->pending;
1340 list_add_tail(&q->list, &pending->list);
....
1347 }
In the first case, the list element we are looking for, ``q``, is being
returned from the function ``__sigqueue_alloc()``, which looks like an
allocation function. Let's take a look at it::
187 static struct sigqueue *__sigqueue_alloc(struct task_struct *t, gfp_t flags,
188 int override_rlimit)
189 {
190 struct sigqueue *q = NULL;
191 struct user_struct *user;
192
193 /*
194 * We won't get problems with the target's UID changing under us
195 * because changing it requires RCU be used, and if t != current, the
196 * caller must be holding the RCU readlock (by way of a spinlock) and
197 * we use RCU protection here
198 */
199 user = get_uid(__task_cred(t)->user);
200 atomic_inc(&user->sigpending);
201 if (override_rlimit ||
202 atomic_read(&user->sigpending) <=
203 t->signal->rlim[RLIMIT_SIGPENDING].rlim_cur)
204 q = kmem_cache_alloc(sigqueue_cachep, flags);
205 if (unlikely(q == NULL)) {
206 atomic_dec(&user->sigpending);
207 free_uid(user);
208 } else {
209 INIT_LIST_HEAD(&q->list);
210 q->flags = 0;
211 q->user = user;
212 }
213
214 return q;
215 }
We see that this function initializes ``q->list``, ``q->flags``, and
``q->user``. It seems that now is the time to look at the definition of
``struct sigqueue``, e.g.::
14 struct sigqueue {
15 struct list_head list;
16 int flags;
17 siginfo_t info;
18 struct user_struct *user;
19 };
And, you might remember, it was a ``memcpy()`` on ``&first->info`` that
caused the warning, so this makes perfect sense. It also seems reasonable
to assume that it is the caller of ``__sigqueue_alloc()`` that has the
responsibility of filling out (initializing) this member.
But just which fields of the struct were uninitialized? Let's look at
kmemcheck's report again::
WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (ffff88003e4a2024)
80000000000000000000000000000000000000000088ffff0000000000000000
i i i i u u u u i i i i i i i i u u u u u u u u u u u u u u u u
^
These first two lines are the memory dump of the memory object itself, and
the shadow bytemap, respectively. The memory object itself is in this case
``&first->info``. Just beware that the start of this dump is NOT the start
of the object itself! The position of the caret (^) corresponds with the
address of the read (ffff88003e4a2024).
The shadow bytemap dump legend is as follows:
- i: initialized
- u: uninitialized
- a: unallocated (memory has been allocated by the slab layer, but has not
yet been handed off to anybody)
- f: freed (memory has been allocated by the slab layer, but has been freed
by the previous owner)
In order to figure out where (relative to the start of the object) the
uninitialized memory was located, we have to look at the disassembly. For
that, we'll need the RIP address again::
RIP: 0010:[<ffffffff8104ede8>] [<ffffffff8104ede8>] __dequeue_signal+0xc8/0x190
$ objdump -d --no-show-raw-insn vmlinux | grep -C 8 ffffffff8104ede8:
ffffffff8104edc8: mov %r8,0x8(%r8)
ffffffff8104edcc: test %r10d,%r10d
ffffffff8104edcf: js ffffffff8104ee88 <__dequeue_signal+0x168>
ffffffff8104edd5: mov %rax,%rdx
ffffffff8104edd8: mov $0xc,%ecx
ffffffff8104eddd: mov %r13,%rdi
ffffffff8104ede0: mov $0x30,%eax
ffffffff8104ede5: mov %rdx,%rsi
ffffffff8104ede8: rep movsl %ds:(%rsi),%es:(%rdi)
ffffffff8104edea: test $0x2,%al
ffffffff8104edec: je ffffffff8104edf0 <__dequeue_signal+0xd0>
ffffffff8104edee: movsw %ds:(%rsi),%es:(%rdi)
ffffffff8104edf0: test $0x1,%al
ffffffff8104edf2: je ffffffff8104edf5 <__dequeue_signal+0xd5>
ffffffff8104edf4: movsb %ds:(%rsi),%es:(%rdi)
ffffffff8104edf5: mov %r8,%rdi
ffffffff8104edf8: callq ffffffff8104de60 <__sigqueue_free>
As expected, it's the "``rep movsl``" instruction from the ``memcpy()``
that causes the warning. We know about ``REP MOVSL`` that it uses the register
``RCX`` to count the number of remaining iterations. By taking a look at the
register dump again (from the kmemcheck report), we can figure out how many
bytes were left to copy::
RAX: 0000000000000030 RBX: ffff88003d4ea968 RCX: 0000000000000009
By looking at the disassembly, we also see that ``%ecx`` is being loaded
with the value ``$0xc`` just before (ffffffff8104edd8), so we are very
lucky. Keep in mind that this is the number of iterations, not bytes. And
since this is a "long" operation, we need to multiply by 4 to get the
number of bytes. So this means that the uninitialized value was encountered
at 4 * (0xc - 0x9) = 12 bytes from the start of the object.
We can now try to figure out which field of the "``struct siginfo``" that
was not initialized. This is the beginning of the struct::
40 typedef struct siginfo {
41 int si_signo;
42 int si_errno;
43 int si_code;
44
45 union {
..
92 } _sifields;
93 } siginfo_t;
On 64-bit, the int is 4 bytes long, so it must the union member that has
not been initialized. We can verify this using gdb::
$ gdb vmlinux
...
(gdb) p &((struct siginfo *) 0)->_sifields
$1 = (union {...} *) 0x10
Actually, it seems that the union member is located at offset 0x10 -- which
means that gcc has inserted 4 bytes of padding between the members ``si_code``
and ``_sifields``. We can now get a fuller picture of the memory dump::
_----------------------------=> si_code
/ _--------------------=> (padding)
| / _------------=> _sifields(._kill._pid)
| | / _----=> _sifields(._kill._uid)
| | | /
-------|-------|-------|-------|
80000000000000000000000000000000000000000088ffff0000000000000000
i i i i u u u u i i i i i i i i u u u u u u u u u u u u u u u u
This allows us to realize another important fact: ``si_code`` contains the
value 0x80. Remember that x86 is little endian, so the first 4 bytes
"80000000" are really the number 0x00000080. With a bit of research, we
find that this is actually the constant ``SI_KERNEL`` defined in
``include/asm-generic/siginfo.h``::
144 #define SI_KERNEL 0x80 /* sent by the kernel from somewhere */
This macro is used in exactly one place in the x86 kernel: In ``send_signal()``
in ``kernel/signal.c``::
816 static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
817 int group)
818 {
...
828 pending = group ? &t->signal->shared_pending : &t->pending;
...
851 q = __sigqueue_alloc(t, GFP_ATOMIC, (sig < SIGRTMIN &&
852 (is_si_special(info) ||
853 info->si_code >= 0)));
854 if (q) {
855 list_add_tail(&q->list, &pending->list);
856 switch ((unsigned long) info) {
...
865 case (unsigned long) SEND_SIG_PRIV:
866 q->info.si_signo = sig;
867 q->info.si_errno = 0;
868 q->info.si_code = SI_KERNEL;
869 q->info.si_pid = 0;
870 q->info.si_uid = 0;
871 break;
...
890 }
Not only does this match with the ``.si_code`` member, it also matches the place
we found earlier when looking for where siginfo_t objects are enqueued on the
``shared_pending`` list.
So to sum up: It seems that it is the padding introduced by the compiler
between two struct fields that is uninitialized, and this gets reported when
we do a ``memcpy()`` on the struct. This means that we have identified a false
positive warning.
Normally, kmemcheck will not report uninitialized accesses in ``memcpy()`` calls
when both the source and destination addresses are tracked. (Instead, we copy
the shadow bytemap as well). In this case, the destination address clearly
was not tracked. We can dig a little deeper into the stack trace from above::
arch/x86/kernel/signal.c:805
arch/x86/kernel/signal.c:871
arch/x86/kernel/entry_64.S:694
And we clearly see that the destination siginfo object is located on the
stack::
782 static void do_signal(struct pt_regs *regs)
783 {
784 struct k_sigaction ka;
785 siginfo_t info;
...
804 signr = get_signal_to_deliver(&info, &ka, regs, NULL);
...
854 }
And this ``&info`` is what eventually gets passed to ``copy_siginfo()`` as the
destination argument.
Now, even though we didn't find an actual error here, the example is still a
good one, because it shows how one would go about to find out what the report
was all about.
Annotating false positives
~~~~~~~~~~~~~~~~~~~~~~~~~~
There are a few different ways to make annotations in the source code that
will keep kmemcheck from checking and reporting certain allocations. Here
they are:
- ``__GFP_NOTRACK_FALSE_POSITIVE``
This flag can be passed to ``kmalloc()`` or ``kmem_cache_alloc()``
(therefore also to other functions that end up calling one of
these) to indicate that the allocation should not be tracked
because it would lead to a false positive report. This is a "big
hammer" way of silencing kmemcheck; after all, even if the false
positive pertains to particular field in a struct, for example, we
will now lose the ability to find (real) errors in other parts of
the same struct.
Example::
/* No warnings will ever trigger on accessing any part of x */
x = kmalloc(sizeof *x, GFP_KERNEL | __GFP_NOTRACK_FALSE_POSITIVE);
- ``kmemcheck_bitfield_begin(name)``/``kmemcheck_bitfield_end(name)`` and
``kmemcheck_annotate_bitfield(ptr, name)``
The first two of these three macros can be used inside struct
definitions to signal, respectively, the beginning and end of a
bitfield. Additionally, this will assign the bitfield a name, which
is given as an argument to the macros.
Having used these markers, one can later use
kmemcheck_annotate_bitfield() at the point of allocation, to indicate
which parts of the allocation is part of a bitfield.
Example::
struct foo {
int x;
kmemcheck_bitfield_begin(flags);
int flag_a:1;
int flag_b:1;
kmemcheck_bitfield_end(flags);
int y;
};
struct foo *x = kmalloc(sizeof *x);
/* No warnings will trigger on accessing the bitfield of x */
kmemcheck_annotate_bitfield(x, flags);
Note that ``kmemcheck_annotate_bitfield()`` can be used even before the
return value of ``kmalloc()`` is checked -- in other words, passing NULL
as the first argument is legal (and will do nothing).
Reporting errors
----------------
As we have seen, kmemcheck will produce false positive reports. Therefore, it
is not very wise to blindly post kmemcheck warnings to mailing lists and
maintainers. Instead, I encourage maintainers and developers to find errors
in their own code. If you get a warning, you can try to work around it, try
to figure out if it's a real error or not, or simply ignore it. Most
developers know their own code and will quickly and efficiently determine the
root cause of a kmemcheck report. This is therefore also the most efficient
way to work with kmemcheck.
That said, we (the kmemcheck maintainers) will always be on the lookout for
false positives that we can annotate and silence. So whatever you find,
please drop us a note privately! Kernel configs and steps to reproduce (if
available) are of course a great help too.
Happy hacking!
Technical description
---------------------
kmemcheck works by marking memory pages non-present. This means that whenever
somebody attempts to access the page, a page fault is generated. The page
fault handler notices that the page was in fact only hidden, and so it calls
on the kmemcheck code to make further investigations.
When the investigations are completed, kmemcheck "shows" the page by marking
it present (as it would be under normal circumstances). This way, the
interrupted code can continue as usual.
But after the instruction has been executed, we should hide the page again, so
that we can catch the next access too! Now kmemcheck makes use of a debugging
feature of the processor, namely single-stepping. When the processor has
finished the one instruction that generated the memory access, a debug
exception is raised. From here, we simply hide the page again and continue
execution, this time with the single-stepping feature turned off.
kmemcheck requires some assistance from the memory allocator in order to work.
The memory allocator needs to
1. Tell kmemcheck about newly allocated pages and pages that are about to
be freed. This allows kmemcheck to set up and tear down the shadow memory
for the pages in question. The shadow memory stores the status of each
byte in the allocation proper, e.g. whether it is initialized or
uninitialized.
2. Tell kmemcheck which parts of memory should be marked uninitialized.
There are actually a few more states, such as "not yet allocated" and
"recently freed".
If a slab cache is set up using the SLAB_NOTRACK flag, it will never return
memory that can take page faults because of kmemcheck.
If a slab cache is NOT set up using the SLAB_NOTRACK flag, callers can still
request memory with the __GFP_NOTRACK or __GFP_NOTRACK_FALSE_POSITIVE flags.
This does not prevent the page faults from occurring, however, but marks the
object in question as being initialized so that no warnings will ever be
produced for this object.
Currently, the SLAB and SLUB allocators are supported by kmemcheck.

10
MAINTAINERS
View file

@ -7688,16 +7688,6 @@ F: include/linux/kdb.h
F: include/linux/kgdb.h F: include/linux/kgdb.h
F: kernel/debug/ F: kernel/debug/
KMEMCHECK
M: Vegard Nossum <vegardno@ifi.uio.no>
M: Pekka Enberg <penberg@kernel.org>
S: Maintained
F: Documentation/dev-tools/kmemcheck.rst
F: arch/x86/include/asm/kmemcheck.h
F: arch/x86/mm/kmemcheck/
F: include/linux/kmemcheck.h
F: mm/kmemcheck.c
KMEMLEAK KMEMLEAK
M: Catalin Marinas <catalin.marinas@arm.com> M: Catalin Marinas <catalin.marinas@arm.com>
S: Maintained S: Maintained

3
arch/x86/Kconfig
View file

@ -112,7 +112,6 @@ config X86
select HAVE_ARCH_JUMP_LABEL select HAVE_ARCH_JUMP_LABEL
select HAVE_ARCH_KASAN if X86_64 && SPARSEMEM_VMEMMAP select HAVE_ARCH_KASAN if X86_64 && SPARSEMEM_VMEMMAP
select HAVE_ARCH_KGDB select HAVE_ARCH_KGDB
select HAVE_ARCH_KMEMCHECK
select HAVE_ARCH_MMAP_RND_BITS if MMU select HAVE_ARCH_MMAP_RND_BITS if MMU
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT
select HAVE_ARCH_COMPAT_MMAP_BASES if MMU && COMPAT select HAVE_ARCH_COMPAT_MMAP_BASES if MMU && COMPAT
@ -1430,7 +1429,7 @@ config ARCH_DMA_ADDR_T_64BIT
config X86_DIRECT_GBPAGES config X86_DIRECT_GBPAGES
def_bool y def_bool y
depends on X86_64 && !DEBUG_PAGEALLOC && !KMEMCHECK depends on X86_64 && !DEBUG_PAGEALLOC
---help--- ---help---
Certain kernel features effectively disable kernel Certain kernel features effectively disable kernel
linear 1 GB mappings (even if the CPU otherwise linear 1 GB mappings (even if the CPU otherwise

42
arch/x86/include/asm/kmemcheck.h
View file

@ -1,43 +1 @@
/* SPDX-License-Identifier: GPL-2.0 */ /* SPDX-License-Identifier: GPL-2.0 */
#ifndef ASM_X86_KMEMCHECK_H
#define ASM_X86_KMEMCHECK_H
#include <linux/types.h>
#include <asm/ptrace.h>
#ifdef CONFIG_KMEMCHECK
bool kmemcheck_active(struct pt_regs *regs);
void kmemcheck_show(struct pt_regs *regs);
void kmemcheck_hide(struct pt_regs *regs);
bool kmemcheck_fault(struct pt_regs *regs,
unsigned long address, unsigned long error_code);
bool kmemcheck_trap(struct pt_regs *regs);
#else
static inline bool kmemcheck_active(struct pt_regs *regs)
{
return false;
}
static inline void kmemcheck_show(struct pt_regs *regs)
{
}
static inline void kmemcheck_hide(struct pt_regs *regs)
{
}
static inline bool kmemcheck_fault(struct pt_regs *regs,
unsigned long address, unsigned long error_code)
{
return false;
}
static inline bool kmemcheck_trap(struct pt_regs *regs)
{
return false;
}
#endif /* CONFIG_KMEMCHECK */
#endif

9
arch/x86/include/asm/string_32.h
View file

@ -179,8 +179,6 @@ static inline void *__memcpy3d(void *to, const void *from, size_t len)
* No 3D Now! * No 3D Now!
*/ */
#ifndef CONFIG_KMEMCHECK
#if (__GNUC__ >= 4) #if (__GNUC__ >= 4)
#define memcpy(t, f, n) __builtin_memcpy(t, f, n) #define memcpy(t, f, n) __builtin_memcpy(t, f, n)
#else #else
@ -189,13 +187,6 @@ static inline void *__memcpy3d(void *to, const void *from, size_t len)
? __constant_memcpy((t), (f), (n)) \ ? __constant_memcpy((t), (f), (n)) \
: __memcpy((t), (f), (n))) : __memcpy((t), (f), (n)))
#endif #endif
#else
/*
* kmemcheck becomes very happy if we use the REP instructions unconditionally,
* because it means that we know both memory operands in advance.
*/
#define memcpy(t, f, n) __memcpy((t), (f), (n))
#endif
#endif #endif
#endif /* !CONFIG_FORTIFY_SOURCE */ #endif /* !CONFIG_FORTIFY_SOURCE */

8
arch/x86/include/asm/string_64.h
View file

@ -33,7 +33,6 @@ extern void *memcpy(void *to, const void *from, size_t len);
extern void *__memcpy(void *to, const void *from, size_t len); extern void *__memcpy(void *to, const void *from, size_t len);
#ifndef CONFIG_FORTIFY_SOURCE #ifndef CONFIG_FORTIFY_SOURCE
#ifndef CONFIG_KMEMCHECK
#if (__GNUC__ == 4 && __GNUC_MINOR__ < 3) || __GNUC__ < 4 #if (__GNUC__ == 4 && __GNUC_MINOR__ < 3) || __GNUC__ < 4
#define memcpy(dst, src, len) \ #define memcpy(dst, src, len) \
({ \ ({ \
@ -46,13 +45,6 @@ extern void *__memcpy(void *to, const void *from, size_t len);
__ret; \ __ret; \
}) })
#endif #endif
#else
/*
* kmemcheck becomes very happy if we use the REP instructions unconditionally,
* because it means that we know both memory operands in advance.
*/
#define memcpy(dst, src, len) __inline_memcpy((dst), (src), (len))
#endif
#endif /* !CONFIG_FORTIFY_SOURCE */ #endif /* !CONFIG_FORTIFY_SOURCE */
#define __HAVE_ARCH_MEMSET #define __HAVE_ARCH_MEMSET

15
arch/x86/kernel/cpu/intel.c
View file

@ -187,21 +187,6 @@ static void early_init_intel(struct cpuinfo_x86 *c)
if (c->x86 == 6 && c->x86_model < 15) if (c->x86 == 6 && c->x86_model < 15)
clear_cpu_cap(c, X86_FEATURE_PAT); clear_cpu_cap(c, X86_FEATURE_PAT);
#ifdef CONFIG_KMEMCHECK
/*
* P4s have a "fast strings" feature which causes single-
* stepping REP instructions to only generate a #DB on
* cache-line boundaries.
*
* Ingo Molnar reported a Pentium D (model 6) and a Xeon
* (model 2) with the same problem.
*/
if (c->x86 == 15)
if (msr_clear_bit(MSR_IA32_MISC_ENABLE,
MSR_IA32_MISC_ENABLE_FAST_STRING_BIT) > 0)
pr_info("kmemcheck: Disabling fast string operations\n");
#endif
/* /*
* If fast string is not enabled in IA32_MISC_ENABLE for any reason, * If fast string is not enabled in IA32_MISC_ENABLE for any reason,
* clear the fast string and enhanced fast string CPU capabilities. * clear the fast string and enhanced fast string CPU capabilities.

2
arch/x86/mm/Makefile
View file

@ -29,8 +29,6 @@ obj-$(CONFIG_X86_PTDUMP) += debug_pagetables.o
obj-$(CONFIG_HIGHMEM) += highmem_32.o obj-$(CONFIG_HIGHMEM) += highmem_32.o
obj-$(CONFIG_KMEMCHECK) += kmemcheck/
KASAN_SANITIZE_kasan_init_$(BITS).o := n KASAN_SANITIZE_kasan_init_$(BITS).o := n
obj-$(CONFIG_KASAN) += kasan_init_$(BITS).o obj-$(CONFIG_KASAN) += kasan_init_$(BITS).o

5
arch/x86/mm/init.c
View file

@ -163,12 +163,11 @@ static int page_size_mask;
static void __init probe_page_size_mask(void) static void __init probe_page_size_mask(void)
{ {
/* /*
* For CONFIG_KMEMCHECK or pagealloc debugging, identity mapping will * For pagealloc debugging, identity mapping will use small pages.
* use small pages.
* This will simplify cpa(), which otherwise needs to support splitting * This will simplify cpa(), which otherwise needs to support splitting
* large pages into small in interrupt context, etc. * large pages into small in interrupt context, etc.
*/ */
if (boot_cpu_has(X86_FEATURE_PSE) && !debug_pagealloc_enabled() && !IS_ENABLED(CONFIG_KMEMCHECK)) if (boot_cpu_has(X86_FEATURE_PSE) && !debug_pagealloc_enabled())
page_size_mask |= 1 << PG_LEVEL_2M; page_size_mask |= 1 << PG_LEVEL_2M;
else else
direct_gbpages = 0; direct_gbpages = 0;

1
arch/x86/mm/kmemcheck/Makefile
View file

@ -1 +0,0 @@
obj-y := error.o kmemcheck.o opcode.o pte.o selftest.o shadow.o

227
arch/x86/mm/kmemcheck/error.c
View file

@ -1,228 +1 @@
// SPDX-License-Identifier: GPL-2.0 // SPDX-License-Identifier: GPL-2.0
#include <linux/interrupt.h>
#include <linux/kdebug.h>
#include <linux/kmemcheck.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/stacktrace.h>
#include <linux/string.h>
#include "error.h"
#include "shadow.h"
enum kmemcheck_error_type {
KMEMCHECK_ERROR_INVALID_ACCESS,
KMEMCHECK_ERROR_BUG,
};
#define SHADOW_COPY_SIZE (1 << CONFIG_KMEMCHECK_SHADOW_COPY_SHIFT)
struct kmemcheck_error {
enum kmemcheck_error_type type;
union {
/* KMEMCHECK_ERROR_INVALID_ACCESS */
struct {
/* Kind of access that caused the error */
enum kmemcheck_shadow state;
/* Address and size of the erroneous read */
unsigned long address;
unsigned int size;
};
};
struct pt_regs regs;
struct stack_trace trace;
unsigned long trace_entries[32];
/* We compress it to a char. */
unsigned char shadow_copy[SHADOW_COPY_SIZE];
unsigned char memory_copy[SHADOW_COPY_SIZE];
};
/*
* Create a ring queue of errors to output. We can't call printk() directly
* from the kmemcheck traps, since this may call the console drivers and
* result in a recursive fault.
*/
static struct kmemcheck_error error_fifo[CONFIG_KMEMCHECK_QUEUE_SIZE];
static unsigned int error_count;
static unsigned int error_rd;
static unsigned int error_wr;
static unsigned int error_missed_count;
static struct kmemcheck_error *error_next_wr(void)
{
struct kmemcheck_error *e;
if (error_count == ARRAY_SIZE(error_fifo)) {
++error_missed_count;
return NULL;
}
e = &error_fifo[error_wr];
if (++error_wr == ARRAY_SIZE(error_fifo))
error_wr = 0;
++error_count;
return e;
}
static struct kmemcheck_error *error_next_rd(void)
{
struct kmemcheck_error *e;
if (error_count == 0)
return NULL;
e = &error_fifo[error_rd];
if (++error_rd == ARRAY_SIZE(error_fifo))
error_rd = 0;
--error_count;
return e;
}
void kmemcheck_error_recall(void)
{
static const char *desc[] = {
[KMEMCHECK_SHADOW_UNALLOCATED] = "unallocated",
[KMEMCHECK_SHADOW_UNINITIALIZED] = "uninitialized",
[KMEMCHECK_SHADOW_INITIALIZED] = "initialized",
[KMEMCHECK_SHADOW_FREED] = "freed",
};
static const char short_desc[] = {
[KMEMCHECK_SHADOW_UNALLOCATED] = 'a',
[KMEMCHECK_SHADOW_UNINITIALIZED] = 'u',
[KMEMCHECK_SHADOW_INITIALIZED] = 'i',
[KMEMCHECK_SHADOW_FREED] = 'f',
};
struct kmemcheck_error *e;
unsigned int i;
e = error_next_rd();
if (!e)
return;
switch (e->type) {
case KMEMCHECK_ERROR_INVALID_ACCESS:
printk(KERN_WARNING "WARNING: kmemcheck: Caught %d-bit read from %s memory (%p)\n",
8 * e->size, e->state < ARRAY_SIZE(desc) ?
desc[e->state] : "(invalid shadow state)",
(void *) e->address);
printk(KERN_WARNING);
for (i = 0; i < SHADOW_COPY_SIZE; ++i)
printk(KERN_CONT "%02x", e->memory_copy[i]);
printk(KERN_CONT "\n");
printk(KERN_WARNING);
for (i = 0; i < SHADOW_COPY_SIZE; ++i) {
if (e->shadow_copy[i] < ARRAY_SIZE(short_desc))
printk(KERN_CONT " %c", short_desc[e->shadow_copy[i]]);
else
printk(KERN_CONT " ?");
}
printk(KERN_CONT "\n");
printk(KERN_WARNING "%*c\n", 2 + 2
* (int) (e->address & (SHADOW_COPY_SIZE - 1)), '^');
break;
case KMEMCHECK_ERROR_BUG:
printk(KERN_EMERG "ERROR: kmemcheck: Fatal error\n");
break;
}
__show_regs(&e->regs, 1);
print_stack_trace(&e->trace, 0);
}
static void do_wakeup(unsigned long data)
{
while (error_count > 0)
kmemcheck_error_recall();
if (error_missed_count > 0) {
printk(KERN_WARNING "kmemcheck: Lost %d error reports because "
"the queue was too small\n", error_missed_count);
error_missed_count = 0;
}
}
static DECLARE_TASKLET(kmemcheck_tasklet, &do_wakeup, 0);
/*
* Save the context of an error report.
*/
void kmemcheck_error_save(enum kmemcheck_shadow state,
unsigned long address, unsigned int size, struct pt_regs *regs)
{
static unsigned long prev_ip;
struct kmemcheck_error *e;
void *shadow_copy;
void *memory_copy;
/* Don't report several adjacent errors from the same EIP. */
if (regs->ip == prev_ip)
return;
prev_ip = regs->ip;
e = error_next_wr();
if (!e)
return;
e->type = KMEMCHECK_ERROR_INVALID_ACCESS;
e->state = state;
e->address = address;
e->size = size;
/* Save regs */
memcpy(&e->regs, regs, sizeof(*regs));
/* Save stack trace */
e->trace.nr_entries = 0;
e->trace.entries = e->trace_entries;
e->trace.max_entries = ARRAY_SIZE(e->trace_entries);
e->trace.skip = 0;
save_stack_trace_regs(regs, &e->trace);
/* Round address down to nearest 16 bytes */
shadow_copy = kmemcheck_shadow_lookup(address
& ~(SHADOW_COPY_SIZE - 1));
BUG_ON(!shadow_copy);
memcpy(e->shadow_copy, shadow_copy, SHADOW_COPY_SIZE);
kmemcheck_show_addr(address);
memory_copy = (void *) (address & ~(SHADOW_COPY_SIZE - 1));
memcpy(e->memory_copy, memory_copy, SHADOW_COPY_SIZE);
kmemcheck_hide_addr(address);
tasklet_hi_schedule_first(&kmemcheck_tasklet);
}
/*
* Save the context of a kmemcheck bug.
*/
void kmemcheck_error_save_bug(struct pt_regs *regs)
{
struct kmemcheck_error *e;
e = error_next_wr();
if (!e)
return;
e->type = KMEMCHECK_ERROR_BUG;
memcpy(&e->regs, regs, sizeof(*regs));
e->trace.nr_entries = 0;
e->trace.entries = e->trace_entries;
e->trace.max_entries = ARRAY_SIZE(e->trace_entries);
e->trace.skip = 1;
save_stack_trace(&e->trace);
tasklet_hi_schedule_first(&kmemcheck_tasklet);
}

15
arch/x86/mm/kmemcheck/error.h
View file

@ -1,16 +1 @@
/* SPDX-License-Identifier: GPL-2.0 */ /* SPDX-License-Identifier: GPL-2.0 */
#ifndef ARCH__X86__MM__KMEMCHECK__ERROR_H
#define ARCH__X86__MM__KMEMCHECK__ERROR_H
#include <linux/ptrace.h>
#include "shadow.h"
void kmemcheck_error_save(enum kmemcheck_shadow state,
unsigned long address, unsigned int size, struct pt_regs *regs);
void kmemcheck_error_save_bug(struct pt_regs *regs);
void kmemcheck_error_recall(void);
#endif

658
arch/x86/mm/kmemcheck/kmemcheck.c
View file

@ -1,658 +0,0 @@
/**
* kmemcheck - a heavyweight memory checker for the linux kernel
* Copyright (C) 2007, 2008 Vegard Nossum <vegardno@ifi.uio.no>
* (With a lot of help from Ingo Molnar and Pekka Enberg.)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License (version 2) as
* published by the Free Software Foundation.
*/
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kallsyms.h>
#include <linux/kernel.h>
#include <linux/kmemcheck.h>
#include <linux/mm.h>
#include <linux/page-flags.h>
#include <linux/percpu.h>
#include <linux/ptrace.h>
#include <linux/string.h>
#include <linux/types.h>
#include <asm/cacheflush.h>
#include <asm/kmemcheck.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include "error.h"
#include "opcode.h"
#include "pte.h"
#include "selftest.h"
#include "shadow.h"
#ifdef CONFIG_KMEMCHECK_DISABLED_BY_DEFAULT
# define KMEMCHECK_ENABLED 0
#endif
#ifdef CONFIG_KMEMCHECK_ENABLED_BY_DEFAULT
# define KMEMCHECK_ENABLED 1
#endif
#ifdef CONFIG_KMEMCHECK_ONESHOT_BY_DEFAULT
# define KMEMCHECK_ENABLED 2
#endif
int kmemcheck_enabled = KMEMCHECK_ENABLED;
int __init kmemcheck_init(void)
{
#ifdef CONFIG_SMP
/*
* Limit SMP to use a single CPU. We rely on the fact that this code
* runs before SMP is set up.
*/
if (setup_max_cpus > 1) {
printk(KERN_INFO
"kmemcheck: Limiting number of CPUs to 1.\n");
setup_max_cpus = 1;
}
#endif
if (!kmemcheck_selftest()) {
printk(KERN_INFO "kmemcheck: self-tests failed; disabling\n");
kmemcheck_enabled = 0;
return -EINVAL;
}
printk(KERN_INFO "kmemcheck: Initialized\n");
return 0;
}
early_initcall(kmemcheck_init);
/*
* We need to parse the kmemcheck= option before any memory is allocated.
*/
static int __init param_kmemcheck(char *str)
{
int val;
int ret;
if (!str)
return -EINVAL;
ret = kstrtoint(str, 0, &val);
if (ret)
return ret;
kmemcheck_enabled = val;
return 0;
}
early_param("kmemcheck", param_kmemcheck);
int kmemcheck_show_addr(unsigned long address)
{
pte_t *pte;
pte = kmemcheck_pte_lookup(address);
if (!pte)
return 0;
set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT));
__flush_tlb_one(address);
return 1;
}
int kmemcheck_hide_addr(unsigned long address)
{
pte_t *pte;
pte = kmemcheck_pte_lookup(address);
if (!pte)
return 0;
set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT));
__flush_tlb_one(address);
return 1;
}
struct kmemcheck_context {
bool busy;
int balance;
/*
* There can be at most two memory operands to an instruction, but
* each address can cross a page boundary -- so we may need up to
* four addresses that must be hidden/revealed for each fault.
*/
unsigned long addr[4];
unsigned long n_addrs;
unsigned long flags;
/* Data size of the instruction that caused a fault. */
unsigned int size;
};
static DEFINE_PER_CPU(struct kmemcheck_context, kmemcheck_context);
bool kmemcheck_active(struct pt_regs *regs)
{
struct kmemcheck_context *data = this_cpu_ptr(&kmemcheck_context);
return data->balance > 0;
}
/* Save an address that needs to be shown/hidden */
static void kmemcheck_save_addr(unsigned long addr)
{
struct kmemcheck_context *data = this_cpu_ptr(&kmemcheck_context);
BUG_ON(data->n_addrs >= ARRAY_SIZE(data->addr));
data->addr[data->n_addrs++] = addr;
}
static unsigned int kmemcheck_show_all(void)
{
struct kmemcheck_context *data = this_cpu_ptr(&kmemcheck_context);
unsigned int i;
unsigned int n;
n = 0;
for (i = 0; i < data->n_addrs; ++i)
n += kmemcheck_show_addr(data->addr[i]);
return n;
}
static unsigned int kmemcheck_hide_all(void)
{
struct kmemcheck_context *data = this_cpu_ptr(&kmemcheck_context);
unsigned int i;
unsigned int n;
n = 0;
for (i = 0; i < data->n_addrs; ++i)
n += kmemcheck_hide_addr(data->addr[i]);
return n;
}
/*
* Called from the #PF handler.
*/
void kmemcheck_show(struct pt_regs *regs)
{
struct kmemcheck_context *data = this_cpu_ptr(&kmemcheck_context);
BUG_ON(!irqs_disabled());
if (unlikely(data->balance != 0)) {
kmemcheck_show_all();
kmemcheck_error_save_bug(regs);
data->balance = 0;
return;
}
/*
* None of the addresses actually belonged to kmemcheck. Note that
* this is not an error.
*/
if (kmemcheck_show_all() == 0)
return;
++data->balance;
/*
* The IF needs to be cleared as well, so that the faulting
* instruction can run "uninterrupted". Otherwise, we might take
* an interrupt and start executing that before we've had a chance
* to hide the page again.
*
* NOTE: In the rare case of multiple faults, we must not override
* the original flags:
*/
if (!(regs->flags & X86_EFLAGS_TF))
data->flags = regs->flags;
regs->flags |= X86_EFLAGS_TF;
regs->flags &= ~X86_EFLAGS_IF;
}
/*
* Called from the #DB handler.
*/
void kmemcheck_hide(struct pt_regs *regs)
{
struct kmemcheck_context *data = this_cpu_ptr(&kmemcheck_context);
int n;
BUG_ON(!irqs_disabled());
if (unlikely(data->balance != 1)) {
kmemcheck_show_all();
kmemcheck_error_save_bug(regs);
data->n_addrs = 0;
data->balance = 0;
if (!(data->flags & X86_EFLAGS_TF))
regs->flags &= ~X86_EFLAGS_TF;
if (data->flags & X86_EFLAGS_IF)
regs->flags |= X86_EFLAGS_IF;
return;
}
if (kmemcheck_enabled)
n = kmemcheck_hide_all();
else
n = kmemcheck_show_all();
if (n == 0)
return;
--data->balance;
data->n_addrs = 0;
if (!(data->flags & X86_EFLAGS_TF))
regs->flags &= ~X86_EFLAGS_TF;
if (data->flags & X86_EFLAGS_IF)
regs->flags |= X86_EFLAGS_IF;
}
void kmemcheck_show_pages(struct page *p, unsigned int n)
{
unsigned int i;
for (i = 0; i < n; ++i) {
unsigned long address;
pte_t *pte;
unsigned int level;
address = (unsigned long) page_address(&p[i]);
pte = lookup_address(address, &level);
BUG_ON(!pte);
BUG_ON(level != PG_LEVEL_4K);
set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT));
set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_HIDDEN));
__flush_tlb_one(address);
}
}
bool kmemcheck_page_is_tracked(struct page *p)
{
/* This will also check the "hidden" flag of the PTE. */
return kmemcheck_pte_lookup((unsigned long) page_address(p));
}
void kmemcheck_hide_pages(struct page *p, unsigned int n)
{
unsigned int i;
for (i = 0; i < n; ++i) {
unsigned long address;
pte_t *pte;
unsigned int level;
address = (unsigned long) page_address(&p[i]);
pte = lookup_address(address, &level);
BUG_ON(!pte);
BUG_ON(level != PG_LEVEL_4K);
set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT));
set_pte(pte, __pte(pte_val(*pte) | _PAGE_HIDDEN));
__flush_tlb_one(address);
}
}
/* Access may NOT cross page boundary */
static void kmemcheck_read_strict(struct pt_regs *regs,
unsigned long addr, unsigned int size)
{
void *shadow;
enum kmemcheck_shadow status;
shadow = kmemcheck_shadow_lookup(addr);
if (!shadow)
return;
kmemcheck_save_addr(addr);
status = kmemcheck_shadow_test(shadow, size);
if (status == KMEMCHECK_SHADOW_INITIALIZED)
return;
if (kmemcheck_enabled)
kmemcheck_error_save(status, addr, size, regs);
if (kmemcheck_enabled == 2)
kmemcheck_enabled = 0;
/* Don't warn about it again. */
kmemcheck_shadow_set(shadow, size);
}
bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
{
enum kmemcheck_shadow status;
void *shadow;
shadow = kmemcheck_shadow_lookup(addr);
if (!shadow)
return true;
status = kmemcheck_shadow_test_all(shadow, size);
return status == KMEMCHECK_SHADOW_INITIALIZED;
}
/* Access may cross page boundary */
static void kmemcheck_read(struct pt_regs *regs,
unsigned long addr, unsigned int size)
{
unsigned long page = addr & PAGE_MASK;
unsigned long next_addr = addr + size - 1;
unsigned long next_page = next_addr & PAGE_MASK;
if (likely(page == next_page)) {
kmemcheck_read_strict(regs, addr, size);
return;
}
/*
* What we do is basically to split the access across the
* two pages and handle each part separately. Yes, this means
* that we may now see reads that are 3 + 5 bytes, for
* example (and if both are uninitialized, there will be two
* reports), but it makes the code a lot simpler.
*/
kmemcheck_read_strict(regs, addr, next_page - addr);
kmemcheck_read_strict(regs, next_page, next_addr - next_page);
}
static void kmemcheck_write_strict(struct pt_regs *regs,
unsigned long addr, unsigned int size)
{
void *shadow;
shadow = kmemcheck_shadow_lookup(addr);
if (!shadow)
return;
kmemcheck_save_addr(addr);
kmemcheck_shadow_set(shadow, size);
}
static void kmemcheck_write(struct pt_regs *regs,
unsigned long addr, unsigned int size)
{
unsigned long page = addr & PAGE_MASK;
unsigned long next_addr = addr + size - 1;
unsigned long next_page = next_addr & PAGE_MASK;
if (likely(page == next_page)) {
kmemcheck_write_strict(regs, addr, size);
return;
}
/* See comment in kmemcheck_read(). */
kmemcheck_write_strict(regs, addr, next_page - addr);
kmemcheck_write_strict(regs, next_page, next_addr - next_page);
}
/*
* Copying is hard. We have two addresses, each of which may be split across
* a page (and each page will have different shadow addresses).
*/
static void kmemcheck_copy(struct pt_regs *regs,
unsigned long src_addr, unsigned long dst_addr, unsigned int size)
{
uint8_t shadow[8];
enum kmemcheck_shadow status;
unsigned long page;
unsigned long next_addr;
unsigned long next_page;
uint8_t *x;
unsigned int i;
unsigned int n;
BUG_ON(size > sizeof(shadow));
page = src_addr & PAGE_MASK;
next_addr = src_addr + size - 1;
next_page = next_addr & PAGE_MASK;
if (likely(page == next_page)) {
/* Same page */
x = kmemcheck_shadow_lookup(src_addr);
if (x) {
kmemcheck_save_addr(src_addr);
for (i = 0; i < size; ++i)
shadow[i] = x[i];
} else {
for (i = 0; i < size; ++i)
shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
}
} else {
n = next_page - src_addr;
BUG_ON(n > sizeof(shadow));
/* First page */
x = kmemcheck_shadow_lookup(src_addr);
if (x) {
kmemcheck_save_addr(src_addr);
for (i = 0; i < n; ++i)
shadow[i] = x[i];
} else {
/* Not tracked */
for (i = 0; i < n; ++i)
shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
}
/* Second page */
x = kmemcheck_shadow_lookup(next_page);
if (x) {
kmemcheck_save_addr(next_page);
for (i = n; i < size; ++i)
shadow[i] = x[i - n];
} else {
/* Not tracked */
for (i = n; i < size; ++i)
shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
}
}
page = dst_addr & PAGE_MASK;
next_addr = dst_addr + size - 1;
next_page = next_addr & PAGE_MASK;
if (likely(page == next_page)) {
/* Same page */
x = kmemcheck_shadow_lookup(dst_addr);
if (x) {
kmemcheck_save_addr(dst_addr);
for (i = 0; i < size; ++i) {
x[i] = shadow[i];
shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
}
}
} else {
n = next_page - dst_addr;
BUG_ON(n > sizeof(shadow));
/* First page */
x = kmemcheck_shadow_lookup(dst_addr);
if (x) {
kmemcheck_save_addr(dst_addr);
for (i = 0; i < n; ++i) {
x[i] = shadow[i];
shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
}
}
/* Second page */
x = kmemcheck_shadow_lookup(next_page);
if (x) {
kmemcheck_save_addr(next_page);
for (i = n; i < size; ++i) {
x[i - n] = shadow[i];
shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
}
}
}
status = kmemcheck_shadow_test(shadow, size);
if (status == KMEMCHECK_SHADOW_INITIALIZED)
return;
if (kmemcheck_enabled)
kmemcheck_error_save(status, src_addr, size, regs);
if (kmemcheck_enabled == 2)
kmemcheck_enabled = 0;
}
enum kmemcheck_method {
KMEMCHECK_READ,
KMEMCHECK_WRITE,
};
static void kmemcheck_access(struct pt_regs *regs,
unsigned long fallback_address, enum kmemcheck_method fallback_method)
{
const uint8_t *insn;
const uint8_t *insn_primary;
unsigned int size;
struct kmemcheck_context *data = this_cpu_ptr(&kmemcheck_context);
/* Recursive fault -- ouch. */
if (data->busy) {
kmemcheck_show_addr(fallback_address);
kmemcheck_error_save_bug(regs);
return;
}
data->busy = true;
insn = (const uint8_t *) regs->ip;
insn_primary = kmemcheck_opcode_get_primary(insn);
kmemcheck_opcode_decode(insn, &size);
switch (insn_primary[0]) {
#ifdef CONFIG_KMEMCHECK_BITOPS_OK
/* AND, OR, XOR */
/*
* Unfortunately, these instructions have to be excluded from
* our regular checking since they access only some (and not
* all) bits. This clears out "bogus" bitfield-access warnings.
*/
case 0x80:
case 0x81:
case 0x82:
case 0x83:
switch ((insn_primary[1] >> 3) & 7) {
/* OR */
case 1:
/* AND */
case 4:
/* XOR */
case 6:
kmemcheck_write(regs, fallback_address, size);
goto out;
/* ADD */
case 0:
/* ADC */
case 2:
/* SBB */
case 3:
/* SUB */
case 5:
/* CMP */
case 7:
break;
}
break;
#endif
/* MOVS, MOVSB, MOVSW, MOVSD */
case 0xa4:
case 0xa5:
/*
* These instructions are special because they take two
* addresses, but we only get one page fault.
*/
kmemcheck_copy(regs, regs->si, regs->di, size);
goto out;
/* CMPS, CMPSB, CMPSW, CMPSD */
case 0xa6:
case 0xa7:
kmemcheck_read(regs, regs->si, size);
kmemcheck_read(regs, regs->di, size);
goto out;
}
/*
* If the opcode isn't special in any way, we use the data from the
* page fault handler to determine the address and type of memory
* access.
*/
switch (fallback_method) {
case KMEMCHECK_READ:
kmemcheck_read(regs, fallback_address, size);
goto out;
case KMEMCHECK_WRITE:
kmemcheck_write(regs, fallback_address, size);
goto out;
}
out:
data->busy = false;
}
bool kmemcheck_fault(struct pt_regs *regs, unsigned long address,
unsigned long error_code)
{
pte_t *pte;
/*
* XXX: Is it safe to assume that memory accesses from virtual 86
* mode or non-kernel code segments will _never_ access kernel
* memory (e.g. tracked pages)? For now, we need this to avoid
* invoking kmemcheck for PnP BIOS calls.
*/
if (regs->flags & X86_VM_MASK)
return false;
if (regs->cs != __KERNEL_CS)
return false;
pte = kmemcheck_pte_lookup(address);
if (!pte)
return false;
WARN_ON_ONCE(in_nmi());
if (error_code & 2)
kmemcheck_access(regs, address, KMEMCHECK_WRITE);
else
kmemcheck_access(regs, address, KMEMCHECK_READ);
kmemcheck_show(regs);
return true;
}
bool kmemcheck_trap(struct pt_regs *regs)
{
if (!kmemcheck_active(regs))
return false;
/* We're done. */
kmemcheck_hide(regs);
return true;
}

106
arch/x86/mm/kmemcheck/opcode.c
View file

@ -1,107 +1 @@
// SPDX-License-Identifier: GPL-2.0 // SPDX-License-Identifier: GPL-2.0
#include <linux/types.h>
#include "opcode.h"
static bool opcode_is_prefix(uint8_t b)
{
return
/* Group 1 */
b == 0xf0 || b == 0xf2 || b == 0xf3
/* Group 2 */
|| b == 0x2e || b == 0x36 || b == 0x3e || b == 0x26
|| b == 0x64 || b == 0x65
/* Group 3 */
|| b == 0x66
/* Group 4 */
|| b == 0x67;
}
#ifdef CONFIG_X86_64
static bool opcode_is_rex_prefix(uint8_t b)
{
return (b & 0xf0) == 0x40;
}
#else
static bool opcode_is_rex_prefix(uint8_t b)
{
return false;
}
#endif
#define REX_W (1 << 3)
/*
* This is a VERY crude opcode decoder. We only need to find the size of the
* load/store that caused our #PF and this should work for all the opcodes
* that we care about. Moreover, the ones who invented this instruction set
* should be shot.
*/
void kmemcheck_opcode_decode(const uint8_t *op, unsigned int *size)
{
/* Default operand size */
int operand_size_override = 4;
/* prefixes */
for (; opcode_is_prefix(*op); ++op) {
if (*op == 0x66)
operand_size_override = 2;
}
/* REX prefix */
if (opcode_is_rex_prefix(*op)) {
uint8_t rex = *op;
++op;
if (rex & REX_W) {
switch (*op) {
case 0x63:
*size = 4;
return;
case 0x0f:
++op;
switch (*op) {
case 0xb6:
case 0xbe:
*size = 1;
return;
case 0xb7:
case 0xbf:
*size = 2;
return;
}
break;
}
*size = 8;
return;
}
}
/* escape opcode */
if (*op == 0x0f) {
++op;
/*
* This is move with zero-extend and sign-extend, respectively;
* we don't have to think about 0xb6/0xbe, because this is
* already handled in the conditional below.
*/
if (*op == 0xb7 || *op == 0xbf)
operand_size_override = 2;
}
*size = (*op & 1) ? operand_size_override : 1;
}
const uint8_t *kmemcheck_opcode_get_primary(const uint8_t *op)
{
/* skip prefixes */
while (opcode_is_prefix(*op))
++op;
if (opcode_is_rex_prefix(*op))
++op;
return op;
}

9
arch/x86/mm/kmemcheck/opcode.h
View file

@ -1,10 +1 @@
/* SPDX-License-Identifier: GPL-2.0 */ /* SPDX-License-Identifier: GPL-2.0 */
#ifndef ARCH__X86__MM__KMEMCHECK__OPCODE_H
#define ARCH__X86__MM__KMEMCHECK__OPCODE_H
#include <linux/types.h>
void kmemcheck_opcode_decode(const uint8_t *op, unsigned int *size);
const uint8_t *kmemcheck_opcode_get_primary(const uint8_t *op);
#endif

22
arch/x86/mm/kmemcheck/pte.c
View file

@ -1,23 +1 @@
// SPDX-License-Identifier: GPL-2.0 // SPDX-License-Identifier: GPL-2.0
#include <linux/mm.h>
#include <asm/pgtable.h>
#include "pte.h"
pte_t *kmemcheck_pte_lookup(unsigned long address)
{
pte_t *pte;
unsigned int level;
pte = lookup_address(address, &level);
if (!pte)
return NULL;
if (level != PG_LEVEL_4K)
return NULL;
if (!pte_hidden(*pte))
return NULL;
return pte;
}

10
arch/x86/mm/kmemcheck/pte.h
View file

@ -1,11 +1 @@
/* SPDX-License-Identifier: GPL-2.0 */ /* SPDX-License-Identifier: GPL-2.0 */
#ifndef ARCH__X86__MM__KMEMCHECK__PTE_H
#define ARCH__X86__MM__KMEMCHECK__PTE_H
#include <linux/mm.h>
#include <asm/pgtable.h>
pte_t *kmemcheck_pte_lookup(unsigned long address);
#endif

70
arch/x86/mm/kmemcheck/selftest.c
View file

@ -1,71 +1 @@
// SPDX-License-Identifier: GPL-2.0 // SPDX-License-Identifier: GPL-2.0
#include <linux/bug.h>
#include <linux/kernel.h>
#include "opcode.h"
#include "selftest.h"
struct selftest_opcode {
unsigned int expected_size;
const uint8_t *insn;
const char *desc;
};
static const struct selftest_opcode selftest_opcodes[] = {
/* REP MOVS */
{1, "\xf3\xa4", "rep movsb <mem8>, <mem8>"},
{4, "\xf3\xa5", "rep movsl <mem32>, <mem32>"},
/* MOVZX / MOVZXD */
{1, "\x66\x0f\xb6\x51\xf8", "movzwq <mem8>, <reg16>"},
{1, "\x0f\xb6\x51\xf8", "movzwq <mem8>, <reg32>"},
/* MOVSX / MOVSXD */
{1, "\x66\x0f\xbe\x51\xf8", "movswq <mem8>, <reg16>"},
{1, "\x0f\xbe\x51\xf8", "movswq <mem8>, <reg32>"},
#ifdef CONFIG_X86_64
/* MOVZX / MOVZXD */
{1, "\x49\x0f\xb6\x51\xf8", "movzbq <mem8>, <reg64>"},
{2, "\x49\x0f\xb7\x51\xf8", "movzbq <mem16>, <reg64>"},
/* MOVSX / MOVSXD */
{1, "\x49\x0f\xbe\x51\xf8", "movsbq <mem8>, <reg64>"},
{2, "\x49\x0f\xbf\x51\xf8", "movsbq <mem16>, <reg64>"},
{4, "\x49\x63\x51\xf8", "movslq <mem32>, <reg64>"},
#endif
};
static bool selftest_opcode_one(const struct selftest_opcode *op)
{
unsigned size;
kmemcheck_opcode_decode(op->insn, &size);
if (size == op->expected_size)
return true;
printk(KERN_WARNING "kmemcheck: opcode %s: expected size %d, got %d\n",
op->desc, op->expected_size, size);
return false;
}
static bool selftest_opcodes_all(void)
{
bool pass = true;
unsigned int i;
for (i = 0; i < ARRAY_SIZE(selftest_opcodes); ++i)
pass = pass && selftest_opcode_one(&selftest_opcodes[i]);
return pass;
}
bool kmemcheck_selftest(void)
{
bool pass = true;
pass = pass && selftest_opcodes_all();
return pass;
}

6
arch/x86/mm/kmemcheck/selftest.h
View file

@ -1,7 +1 @@
/* SPDX-License-Identifier: GPL-2.0 */ /* SPDX-License-Identifier: GPL-2.0 */
#ifndef ARCH_X86_MM_KMEMCHECK_SELFTEST_H
#define ARCH_X86_MM_KMEMCHECK_SELFTEST_H
bool kmemcheck_selftest(void);
#endif

173
arch/x86/mm/kmemcheck/shadow.c
View file

@ -1,173 +0,0 @@
#include <linux/kmemcheck.h>
#include <linux/export.h>
#include <linux/mm.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include "pte.h"
#include "shadow.h"
/*
* Return the shadow address for the given address. Returns NULL if the
* address is not tracked.
*
* We need to be extremely careful not to follow any invalid pointers,
* because this function can be called for *any* possible address.
*/
void *kmemcheck_shadow_lookup(unsigned long address)
{
pte_t *pte;
struct page *page;
if (!virt_addr_valid(address))
return NULL;
pte = kmemcheck_pte_lookup(address);
if (!pte)
return NULL;
page = virt_to_page(address);
if (!page->shadow)
return NULL;
return page->shadow + (address & (PAGE_SIZE - 1));
}
static void mark_shadow(void *address, unsigned int n,
enum kmemcheck_shadow status)
{
unsigned long addr = (unsigned long) address;
unsigned long last_addr = addr + n - 1;
unsigned long page = addr & PAGE_MASK;
unsigned long last_page = last_addr & PAGE_MASK;
unsigned int first_n;
void *shadow;
/* If the memory range crosses a page boundary, stop there. */
if (page == last_page)
first_n = n;
else
first_n = page + PAGE_SIZE - addr;
shadow = kmemcheck_shadow_lookup(addr);
if (shadow)
memset(shadow, status, first_n);
addr += first_n;
n -= first_n;
/* Do full-page memset()s. */
while (n >= PAGE_SIZE) {
shadow = kmemcheck_shadow_lookup(addr);
if (shadow)
memset(shadow, status, PAGE_SIZE);
addr += PAGE_SIZE;
n -= PAGE_SIZE;
}
/* Do the remaining page, if any. */
if (n > 0) {
shadow = kmemcheck_shadow_lookup(addr);
if (shadow)
memset(shadow, status, n);
}
}
void kmemcheck_mark_unallocated(void *address, unsigned int n)
{
mark_shadow(address, n, KMEMCHECK_SHADOW_UNALLOCATED);
}
void kmemcheck_mark_uninitialized(void *address, unsigned int n)
{
mark_shadow(address, n, KMEMCHECK_SHADOW_UNINITIALIZED);
}
/*
* Fill the shadow memory of the given address such that the memory at that
* address is marked as being initialized.
*/
void kmemcheck_mark_initialized(void *address, unsigned int n)
{
mark_shadow(address, n, KMEMCHECK_SHADOW_INITIALIZED);
}
EXPORT_SYMBOL_GPL(kmemcheck_mark_initialized);
void kmemcheck_mark_freed(void *address, unsigned int n)
{
mark_shadow(address, n, KMEMCHECK_SHADOW_FREED);
}
void kmemcheck_mark_unallocated_pages(struct page *p, unsigned int n)
{
unsigned int i;
for (i = 0; i < n; ++i)
kmemcheck_mark_unallocated(page_address(&p[i]), PAGE_SIZE);
}
void kmemcheck_mark_uninitialized_pages(struct page *p, unsigned int n)
{
unsigned int i;
for (i = 0; i < n; ++i)
kmemcheck_mark_uninitialized(page_address(&p[i]), PAGE_SIZE);
}
void kmemcheck_mark_initialized_pages(struct page *p, unsigned int n)
{
unsigned int i;
for (i = 0; i < n; ++i)
kmemcheck_mark_initialized(page_address(&p[i]), PAGE_SIZE);
}
enum kmemcheck_shadow kmemcheck_shadow_test(void *shadow, unsigned int size)
{
#ifdef CONFIG_KMEMCHECK_PARTIAL_OK
uint8_t *x;
unsigned int i;
x = shadow;
/*
* Make sure _some_ bytes are initialized. Gcc frequently generates
* code to access neighboring bytes.
*/
for (i = 0; i < size; ++i) {
if (x[i] == KMEMCHECK_SHADOW_INITIALIZED)
return x[i];
}
return x[0];
#else
return kmemcheck_shadow_test_all(shadow, size);
#endif
}
enum kmemcheck_shadow kmemcheck_shadow_test_all(void *shadow, unsigned int size)
{
uint8_t *x;
unsigned int i;
x = shadow;
/* All bytes must be initialized. */
for (i = 0; i < size; ++i) {
if (x[i] != KMEMCHECK_SHADOW_INITIALIZED)
return x[i];
}
return x[0];
}
void kmemcheck_shadow_set(void *shadow, unsigned int size)
{
uint8_t *x;
unsigned int i;
x = shadow;
for (i = 0; i < size; ++i)
x[i] = KMEMCHECK_SHADOW_INITIALIZED;
}

18
arch/x86/mm/kmemcheck/shadow.h
View file

@ -1,19 +1 @@
/* SPDX-License-Identifier: GPL-2.0 */ /* SPDX-License-Identifier: GPL-2.0 */
#ifndef ARCH__X86__MM__KMEMCHECK__SHADOW_H
#define ARCH__X86__MM__KMEMCHECK__SHADOW_H
enum kmemcheck_shadow {
KMEMCHECK_SHADOW_UNALLOCATED,
KMEMCHECK_SHADOW_UNINITIALIZED,
KMEMCHECK_SHADOW_INITIALIZED,
KMEMCHECK_SHADOW_FREED,
};
void *kmemcheck_shadow_lookup(unsigned long address);
enum kmemcheck_shadow kmemcheck_shadow_test(void *shadow, unsigned int size);
enum kmemcheck_shadow kmemcheck_shadow_test_all(void *shadow,
unsigned int size);
void kmemcheck_shadow_set(void *shadow, unsigned int size);
#endif

15
include/linux/interrupt.h
View file

@ -594,21 +594,6 @@ static inline void tasklet_hi_schedule(struct tasklet_struct *t)
__tasklet_hi_schedule(t); __tasklet_hi_schedule(t);
} }
extern void __tasklet_hi_schedule_first(struct tasklet_struct *t);
/*
* This version avoids touching any other tasklets. Needed for kmemcheck
* in order not to take any page faults while enqueueing this tasklet;
* consider VERY carefully whether you really need this or
* tasklet_hi_schedule()...
*/
static inline void tasklet_hi_schedule_first(struct tasklet_struct *t)
{
if (!test_and_set_bit(TASKLET_STATE_SCHED, &t->state))
__tasklet_hi_schedule_first(t);
}
static inline void tasklet_disable_nosync(struct tasklet_struct *t) static inline void tasklet_disable_nosync(struct tasklet_struct *t)
{ {
atomic_inc(&t->count); atomic_inc(&t->count);

171
include/linux/kmemcheck.h
View file

@ -1,172 +1 @@
/* SPDX-License-Identifier: GPL-2.0 */ /* SPDX-License-Identifier: GPL-2.0 */
#ifndef LINUX_KMEMCHECK_H
#define LINUX_KMEMCHECK_H
#include <linux/mm_types.h>
#include <linux/types.h>
#ifdef CONFIG_KMEMCHECK
extern int kmemcheck_enabled;
/* The slab-related functions. */
void kmemcheck_alloc_shadow(struct page *page, int order, gfp_t flags, int node);
void kmemcheck_free_shadow(struct page *page, int order);
void kmemcheck_slab_alloc(struct kmem_cache *s, gfp_t gfpflags, void *object,
size_t size);
void kmemcheck_slab_free(struct kmem_cache *s, void *object, size_t size);
void kmemcheck_pagealloc_alloc(struct page *p, unsigned int order,
gfp_t gfpflags);
void kmemcheck_show_pages(struct page *p, unsigned int n);
void kmemcheck_hide_pages(struct page *p, unsigned int n);
bool kmemcheck_page_is_tracked(struct page *p);
void kmemcheck_mark_unallocated(void *address, unsigned int n);
void kmemcheck_mark_uninitialized(void *address, unsigned int n);
void kmemcheck_mark_initialized(void *address, unsigned int n);
void kmemcheck_mark_freed(void *address, unsigned int n);
void kmemcheck_mark_unallocated_pages(struct page *p, unsigned int n);
void kmemcheck_mark_uninitialized_pages(struct page *p, unsigned int n);
void kmemcheck_mark_initialized_pages(struct page *p, unsigned int n);
int kmemcheck_show_addr(unsigned long address);
int kmemcheck_hide_addr(unsigned long address);
bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size);
/*
* Bitfield annotations
*
* How to use: If you have a struct using bitfields, for example
*
* struct a {
* int x:8, y:8;
* };
*
* then this should be rewritten as
*
* struct a {
* kmemcheck_bitfield_begin(flags);
* int x:8, y:8;
* kmemcheck_bitfield_end(flags);
* };
*
* Now the "flags_begin" and "flags_end" members may be used to refer to the
* beginning and end, respectively, of the bitfield (and things like
* &x.flags_begin is allowed). As soon as the struct is allocated, the bit-
* fields should be annotated:
*
* struct a *a = kmalloc(sizeof(struct a), GFP_KERNEL);
* kmemcheck_annotate_bitfield(a, flags);
*/
#define kmemcheck_bitfield_begin(name) \
int name##_begin[0];
#define kmemcheck_bitfield_end(name) \
int name##_end[0];
#define kmemcheck_annotate_bitfield(ptr, name) \
do { \
int _n; \
\
if (!ptr) \
break; \
\
_n = (long) &((ptr)->name##_end) \
- (long) &((ptr)->name##_begin); \
BUILD_BUG_ON(_n < 0); \
\
kmemcheck_mark_initialized(&((ptr)->name##_begin), _n); \
} while (0)
#define kmemcheck_annotate_variable(var) \
do { \
kmemcheck_mark_initialized(&(var), sizeof(var)); \
} while (0) \
#else
#define kmemcheck_enabled 0
static inline void
kmemcheck_alloc_shadow(struct page *page, int order, gfp_t flags, int node)
{
}
static inline void
kmemcheck_free_shadow(struct page *page, int order)
{
}
static inline void
kmemcheck_slab_alloc(struct kmem_cache *s, gfp_t gfpflags, void *object,
size_t size)
{
}
static inline void kmemcheck_slab_free(struct kmem_cache *s, void *object,
size_t size)
{
}
static inline void kmemcheck_pagealloc_alloc(struct page *p,
unsigned int order, gfp_t gfpflags)
{
}
static inline bool kmemcheck_page_is_tracked(struct page *p)
{
return false;
}
static inline void kmemcheck_mark_unallocated(void *address, unsigned int n)
{
}
static inline void kmemcheck_mark_uninitialized(void *address, unsigned int n)
{
}
static inline void kmemcheck_mark_initialized(void *address, unsigned int n)
{
}
static inline void kmemcheck_mark_freed(void *address, unsigned int n)
{
}
static inline void kmemcheck_mark_unallocated_pages(struct page *p,
unsigned int n)
{
}
static inline void kmemcheck_mark_uninitialized_pages(struct page *p,
unsigned int n)
{
}
static inline void kmemcheck_mark_initialized_pages(struct page *p,
unsigned int n)
{
}
static inline bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
{
return true;
}
#define kmemcheck_bitfield_begin(name)
#define kmemcheck_bitfield_end(name)
#define kmemcheck_annotate_bitfield(ptr, name) \
do { \
} while (0)
#define kmemcheck_annotate_variable(var) \
do { \
} while (0)
#endif /* CONFIG_KMEMCHECK */
#endif /* LINUX_KMEMCHECK_H */

10
kernel/softirq.c
View file

@ -486,16 +486,6 @@ void __tasklet_hi_schedule(struct tasklet_struct *t)
} }
EXPORT_SYMBOL(__tasklet_hi_schedule); EXPORT_SYMBOL(__tasklet_hi_schedule);
void __tasklet_hi_schedule_first(struct tasklet_struct *t)
{
lockdep_assert_irqs_disabled();
t->next = __this_cpu_read(tasklet_hi_vec.head);
__this_cpu_write(tasklet_hi_vec.head, t);
__raise_softirq_irqoff(HI_SOFTIRQ);
}
EXPORT_SYMBOL(__tasklet_hi_schedule_first);
static __latent_entropy void tasklet_action(struct softirq_action *a) static __latent_entropy void tasklet_action(struct softirq_action *a)
{ {
struct tasklet_struct *list; struct tasklet_struct *list;

10
kernel/sysctl.c
View file

@ -30,7 +30,6 @@
#include <linux/proc_fs.h> #include <linux/proc_fs.h>
#include <linux/security.h> #include <linux/security.h>
#include <linux/ctype.h> #include <linux/ctype.h>
#include <linux/kmemcheck.h>
#include <linux/kmemleak.h> #include <linux/kmemleak.h>
#include <linux/fs.h> #include <linux/fs.h>
#include <linux/init.h> #include <linux/init.h>
@ -1173,15 +1172,6 @@ static struct ctl_table kern_table[] = {
.extra1 = &zero, .extra1 = &zero,
.extra2 = &one_thousand, .extra2 = &one_thousand,
}, },
#endif
#ifdef CONFIG_KMEMCHECK
{
.procname = "kmemcheck",
.data = &kmemcheck_enabled,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec,
},
#endif #endif
{ {
.procname = "panic_on_warn", .procname = "panic_on_warn",

6
lib/Kconfig.debug
View file

@ -504,7 +504,7 @@ config DEBUG_OBJECTS_ENABLE_DEFAULT
config DEBUG_SLAB config DEBUG_SLAB
bool "Debug slab memory allocations" bool "Debug slab memory allocations"
depends on DEBUG_KERNEL && SLAB && !KMEMCHECK depends on DEBUG_KERNEL && SLAB
help help
Say Y here to have the kernel do limited verification on memory Say Y here to have the kernel do limited verification on memory
allocation as well as poisoning memory on free to catch use of freed allocation as well as poisoning memory on free to catch use of freed
@ -516,7 +516,7 @@ config DEBUG_SLAB_LEAK
config SLUB_DEBUG_ON config SLUB_DEBUG_ON
bool "SLUB debugging on by default" bool "SLUB debugging on by default"
depends on SLUB && SLUB_DEBUG && !KMEMCHECK depends on SLUB && SLUB_DEBUG
default n default n
help help
Boot with debugging on by default. SLUB boots by default with Boot with debugging on by default. SLUB boots by default with
@ -730,8 +730,6 @@ config DEBUG_STACKOVERFLOW
If in doubt, say "N". If in doubt, say "N".
source "lib/Kconfig.kmemcheck"
source "lib/Kconfig.kasan" source "lib/Kconfig.kasan"
endmenu # "Memory Debugging" endmenu # "Memory Debugging"

94
lib/Kconfig.kmemcheck
View file

@ -1,94 +0,0 @@
config HAVE_ARCH_KMEMCHECK
bool
if HAVE_ARCH_KMEMCHECK
menuconfig KMEMCHECK
bool "kmemcheck: trap use of uninitialized memory"
depends on DEBUG_KERNEL
depends on !X86_USE_3DNOW
depends on SLUB || SLAB
depends on !CC_OPTIMIZE_FOR_SIZE
depends on !FUNCTION_TRACER
select FRAME_POINTER
select STACKTRACE
default n
help
This option enables tracing of dynamically allocated kernel memory
to see if memory is used before it has been given an initial value.
Be aware that this requires half of your memory for bookkeeping and
will insert extra code at *every* read and write to tracked memory
thus slow down the kernel code (but user code is unaffected).
The kernel may be started with kmemcheck=0 or kmemcheck=1 to disable
or enable kmemcheck at boot-time. If the kernel is started with
kmemcheck=0, the large memory and CPU overhead is not incurred.
choice
prompt "kmemcheck: default mode at boot"
depends on KMEMCHECK
default KMEMCHECK_ONESHOT_BY_DEFAULT
help
This option controls the default behaviour of kmemcheck when the
kernel boots and no kmemcheck= parameter is given.
config KMEMCHECK_DISABLED_BY_DEFAULT
bool "disabled"
depends on KMEMCHECK
config KMEMCHECK_ENABLED_BY_DEFAULT
bool "enabled"
depends on KMEMCHECK
config KMEMCHECK_ONESHOT_BY_DEFAULT
bool "one-shot"
depends on KMEMCHECK
help
In one-shot mode, only the first error detected is reported before
kmemcheck is disabled.
endchoice
config KMEMCHECK_QUEUE_SIZE
int "kmemcheck: error queue size"
depends on KMEMCHECK
default 64
help
Select the maximum number of errors to store in the queue. Since
errors can occur virtually anywhere and in any context, we need a
temporary storage area which is guarantueed not to generate any
other faults. The queue will be emptied as soon as a tasklet may
be scheduled. If the queue is full, new error reports will be
lost.
config KMEMCHECK_SHADOW_COPY_SHIFT
int "kmemcheck: shadow copy size (5 => 32 bytes, 6 => 64 bytes)"
depends on KMEMCHECK
range 2 8
default 5
help
Select the number of shadow bytes to save along with each entry of
the queue. These bytes indicate what parts of an allocation are
initialized, uninitialized, etc. and will be displayed when an
error is detected to help the debugging of a particular problem.
config KMEMCHECK_PARTIAL_OK
bool "kmemcheck: allow partially uninitialized memory"
depends on KMEMCHECK
default y
help
This option works around certain GCC optimizations that produce
32-bit reads from 16-bit variables where the upper 16 bits are
thrown away afterwards. This may of course also hide some real
bugs.
config KMEMCHECK_BITOPS_OK
bool "kmemcheck: allow bit-field manipulation"
depends on KMEMCHECK
default n
help
This option silences warnings that would be generated for bit-field
accesses where not all the bits are initialized at the same time.
This may also hide some real bugs.
endif

1
mm/Kconfig.debug
View file

@ -11,7 +11,6 @@ config DEBUG_PAGEALLOC
bool "Debug page memory allocations" bool "Debug page memory allocations"
depends on DEBUG_KERNEL depends on DEBUG_KERNEL
depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
depends on !KMEMCHECK
select PAGE_EXTENSION select PAGE_EXTENSION
select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
---help--- ---help---

2
mm/Makefile
View file

@ -17,7 +17,6 @@ KCOV_INSTRUMENT_slub.o := n
KCOV_INSTRUMENT_page_alloc.o := n KCOV_INSTRUMENT_page_alloc.o := n
KCOV_INSTRUMENT_debug-pagealloc.o := n KCOV_INSTRUMENT_debug-pagealloc.o := n
KCOV_INSTRUMENT_kmemleak.o := n KCOV_INSTRUMENT_kmemleak.o := n
KCOV_INSTRUMENT_kmemcheck.o := n
KCOV_INSTRUMENT_memcontrol.o := n KCOV_INSTRUMENT_memcontrol.o := n
KCOV_INSTRUMENT_mmzone.o := n KCOV_INSTRUMENT_mmzone.o := n
KCOV_INSTRUMENT_vmstat.o := n KCOV_INSTRUMENT_vmstat.o := n
@ -70,7 +69,6 @@ obj-$(CONFIG_KSM) += ksm.o
obj-$(CONFIG_PAGE_POISONING) += page_poison.o obj-$(CONFIG_PAGE_POISONING) += page_poison.o
obj-$(CONFIG_SLAB) += slab.o obj-$(CONFIG_SLAB) += slab.o
obj-$(CONFIG_SLUB) += slub.o obj-$(CONFIG_SLUB) += slub.o
obj-$(CONFIG_KMEMCHECK) += kmemcheck.o
obj-$(CONFIG_KASAN) += kasan/ obj-$(CONFIG_KASAN) += kasan/
obj-$(CONFIG_FAILSLAB) += failslab.o obj-$(CONFIG_FAILSLAB) += failslab.o
obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o

125
mm/kmemcheck.c
View file

@ -1,126 +1 @@
// SPDX-License-Identifier: GPL-2.0 // SPDX-License-Identifier: GPL-2.0
#include <linux/gfp.h>
#include <linux/mm_types.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include "slab.h"
#include <linux/kmemcheck.h>
void kmemcheck_alloc_shadow(struct page *page, int order, gfp_t flags, int node)
{
struct page *shadow;
int pages;
int i;
pages = 1 << order;
/*
* With kmemcheck enabled, we need to allocate a memory area for the
* shadow bits as well.
*/
shadow = alloc_pages_node(node, flags, order);
if (!shadow) {
if (printk_ratelimit())
pr_err("kmemcheck: failed to allocate shadow bitmap\n");
return;
}
for(i = 0; i < pages; ++i)
page[i].shadow = page_address(&shadow[i]);
/*
* Mark it as non-present for the MMU so that our accesses to
* this memory will trigger a page fault and let us analyze
* the memory accesses.
*/
kmemcheck_hide_pages(page, pages);
}
void kmemcheck_free_shadow(struct page *page, int order)
{
struct page *shadow;
int pages;
int i;
if (!kmemcheck_page_is_tracked(page))
return;
pages = 1 << order;
kmemcheck_show_pages(page, pages);
shadow = virt_to_page(page[0].shadow);
for(i = 0; i < pages; ++i)
page[i].shadow = NULL;
__free_pages(shadow, order);
}
void kmemcheck_slab_alloc(struct kmem_cache *s, gfp_t gfpflags, void *object,
size_t size)
{
if (unlikely(!object)) /* Skip object if allocation failed */
return;
/*
* Has already been memset(), which initializes the shadow for us
* as well.
*/
if (gfpflags & __GFP_ZERO)
return;
/* No need to initialize the shadow of a non-tracked slab. */
if (s->flags & SLAB_NOTRACK)
return;
if (!kmemcheck_enabled || gfpflags & __GFP_NOTRACK) {
/*
* Allow notracked objects to be allocated from
* tracked caches. Note however that these objects
* will still get page faults on access, they just
* won't ever be flagged as uninitialized. If page
* faults are not acceptable, the slab cache itself
* should be marked NOTRACK.
*/
kmemcheck_mark_initialized(object, size);
} else if (!s->ctor) {
/*
* New objects should be marked uninitialized before
* they're returned to the called.
*/
kmemcheck_mark_uninitialized(object, size);
}
}
void kmemcheck_slab_free(struct kmem_cache *s, void *object, size_t size)
{
/* TODO: RCU freeing is unsupported for now; hide false positives. */
if (!s->ctor && !(s->flags & SLAB_TYPESAFE_BY_RCU))
kmemcheck_mark_freed(object, size);
}
void kmemcheck_pagealloc_alloc(struct page *page, unsigned int order,
gfp_t gfpflags)
{
int pages;
if (gfpflags & (__GFP_HIGHMEM | __GFP_NOTRACK))
return;
pages = 1 << order;
/*
* NOTE: We choose to track GFP_ZERO pages too; in fact, they
* can become uninitialized by copying uninitialized memory
* into them.
*/
/* XXX: Can use zone->node for node? */
kmemcheck_alloc_shadow(page, order, gfpflags, -1);
if (gfpflags & __GFP_ZERO)
kmemcheck_mark_initialized_pages(page, pages);
else
kmemcheck_mark_uninitialized_pages(page, pages);
}

5
mm/slub.c
View file

@ -1371,7 +1371,7 @@ static inline void *slab_free_hook(struct kmem_cache *s, void *x)
* So in order to make the debug calls that expect irqs to be * So in order to make the debug calls that expect irqs to be
* disabled we need to disable interrupts temporarily. * disabled we need to disable interrupts temporarily.
*/ */
#if defined(CONFIG_KMEMCHECK) || defined(CONFIG_LOCKDEP) #ifdef CONFIG_LOCKDEP
{ {
unsigned long flags; unsigned long flags;
@ -1399,8 +1399,7 @@ static inline void slab_free_freelist_hook(struct kmem_cache *s,
* Compiler cannot detect this function can be removed if slab_free_hook() * Compiler cannot detect this function can be removed if slab_free_hook()
* evaluates to nothing. Thus, catch all relevant config debug options here. * evaluates to nothing. Thus, catch all relevant config debug options here.
*/ */
#if defined(CONFIG_KMEMCHECK) || \ #if defined(CONFIG_LOCKDEP) || \
defined(CONFIG_LOCKDEP) || \
defined(CONFIG_DEBUG_KMEMLEAK) || \ defined(CONFIG_DEBUG_KMEMLEAK) || \
defined(CONFIG_DEBUG_OBJECTS_FREE) || \ defined(CONFIG_DEBUG_OBJECTS_FREE) || \
defined(CONFIG_KASAN) defined(CONFIG_KASAN)

2
scripts/kernel-doc
View file

@ -2182,8 +2182,6 @@ sub dump_struct($$) {
# strip comments: # strip comments:
$members =~ s/\/\*.*?\*\///gos; $members =~ s/\/\*.*?\*\///gos;
$nested =~ s/\/\*.*?\*\///gos; $nested =~ s/\/\*.*?\*\///gos;
# strip kmemcheck_bitfield_{begin,end}.*;
$members =~ s/kmemcheck_bitfield_.*?;//gos;
# strip attributes # strip attributes
$members =~ s/__attribute__\s*\(\([a-z,_\*\s\(\)]*\)\)//i; $members =~ s/__attribute__\s*\(\([a-z,_\*\s\(\)]*\)\)//i;
$members =~ s/__aligned\s*\([^;]*\)//gos; $members =~ s/__aligned\s*\([^;]*\)//gos;

8
tools/include/linux/kmemcheck.h
View file

@ -1,9 +1 @@
/* SPDX-License-Identifier: GPL-2.0 */ /* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LIBLOCKDEP_LINUX_KMEMCHECK_H_
#define _LIBLOCKDEP_LINUX_KMEMCHECK_H_
static inline void kmemcheck_mark_initialized(void *address, unsigned int n)
{
}
#endif