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x86/entry/vsyscall: Add CONFIG to control default

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Most modern systems can run with vsyscall=none. In an effort to
provide a way for build-time defaults to lack legacy settings,
this adds a new CONFIG to select the type of vsyscall mapping to
use, similar to the existing "vsyscall" command line parameter.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150813005519.GA11696@www.outflux.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Kees Cook 2015-08-12 17:55:19 -07:00 committed by Ingo Molnar
parent c25be94f28
commit 3dc33bd30f
2 changed files with 57 additions and 1 deletions
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49
arch/x86/Kconfig
View file

@ -2042,6 +2042,55 @@ config COMPAT_VDSO
If unsure, say N: if you are compiling your own kernel, you
are unlikely to be using a buggy version of glibc.
choice
prompt "vsyscall table for legacy applications"
depends on X86_64
default LEGACY_VSYSCALL_EMULATE
help
Legacy user code that does not know how to find the vDSO expects
to be able to issue three syscalls by calling fixed addresses in
kernel space. Since this location is not randomized with ASLR,
it can be used to assist security vulnerability exploitation.
This setting can be changed at boot time via the kernel command
line parameter vsyscall=[native|emulate|none].
On a system with recent enough glibc (2.14 or newer) and no
static binaries, you can say None without a performance penalty
to improve security.
If unsure, select "Emulate".
config LEGACY_VSYSCALL_NATIVE
bool "Native"
help
Actual executable code is located in the fixed vsyscall
address mapping, implementing time() efficiently. Since
this makes the mapping executable, it can be used during
security vulnerability exploitation (traditionally as
ROP gadgets). This configuration is not recommended.
config LEGACY_VSYSCALL_EMULATE
bool "Emulate"
help
The kernel traps and emulates calls into the fixed
vsyscall address mapping. This makes the mapping
non-executable, but it still contains known contents,
which could be used in certain rare security vulnerability
exploits. This configuration is recommended when userspace
still uses the vsyscall area.
config LEGACY_VSYSCALL_NONE
bool "None"
help
There will be no vsyscall mapping at all. This will
eliminate any risk of ASLR bypass due to the vsyscall
fixed address mapping. Attempts to use the vsyscalls
will be reported to dmesg, so that either old or
malicious userspace programs can be identified.
endchoice
config CMDLINE_BOOL
bool "Built-in kernel command line"
---help---

9
arch/x86/entry/vsyscall/vsyscall_64.c
View file

@ -38,7 +38,14 @@
#define CREATE_TRACE_POINTS
#include "vsyscall_trace.h"
static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE;
static enum { EMULATE, NATIVE, NONE } vsyscall_mode =
#ifdef CONFIG_LEGACY_VSYSCALL_NATIVE
NATIVE;
#elif CONFIG_LEGACY_VSYSCALL_NONE
NONE;
#else
EMULATE;
#endif
static int __init vsyscall_setup(char *str)
{