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x86: Default to vsyscall=native for now

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This UML breakage:

  linux-2.6.30.1[3800] vsyscall fault (exploit attempt?) ip:ffffffffff600000 cs:33 sp:7fbfb9c498 ax:ffffffffff600000 si:0 di:606790
  linux-2.6.30.1[3856] vsyscall fault (exploit attempt?) ip:ffffffffff600000 cs:33 sp:7fbfb13168 ax:ffffffffff600000 si:0 di:606790

Is caused by commit 3ae36655 ("x86-64: Rework vsyscall emulation and add
vsyscall= parameter") - the vsyscall emulation code is not fully cooked
yet as UML relies on some rather fragile SIGSEGV semantics.

Linus suggested in https://lkml.org/lkml/2011/8/9/376 to default
to vsyscall=native for now, this patch implements that.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Andrew Lutomirski <luto@mit.edu>
Cc: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/20111005214047.GE14406@localhost.pp.htv.fi
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Adrian Bunk 2011-10-06 00:40:47 +03:00 committed by Ingo Molnar
parent 65112dccf8
commit 2b666859ec
2 changed files with 5 additions and 4 deletions
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7
Documentation/kernel-parameters.txt
View file

@ -2706,10 +2706,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
functions are at fixed addresses, they make nice
targets for exploits that can control RIP.
emulate [default] Vsyscalls turn into traps and are
emulated reasonably safely.
emulate Vsyscalls turn into traps and are emulated
reasonably safely.
native Vsyscalls are native syscall instructions.
native [default] Vsyscalls are native syscall
instructions.
This is a little bit faster than trapping
and makes a few dynamic recompilers work
better than they would in emulation mode.

2
arch/x86/kernel/vsyscall_64.c
View file

@ -56,7 +56,7 @@ DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data) =
.lock = __SEQLOCK_UNLOCKED(__vsyscall_gtod_data.lock),
};
static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE;
static enum { EMULATE, NATIVE, NONE } vsyscall_mode = NATIVE;
static int __init vsyscall_setup(char *str)
{