From 2b666859ec323403ac9a3a441d16eab30945404b Mon Sep 17 00:00:00 2001 From: Adrian Bunk Date: Thu, 6 Oct 2011 00:40:47 +0300 Subject: [PATCH] x86: Default to vsyscall=native for now 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 Acked-by: Andrew Lutomirski Cc: H. Peter Anvin Link: http://lkml.kernel.org/r/20111005214047.GE14406@localhost.pp.htv.fi Signed-off-by: Ingo Molnar --- Documentation/kernel-parameters.txt | 7 ++++--- arch/x86/kernel/vsyscall_64.c | 2 +- 2 files changed, 5 insertions(+), 4 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 854ed5ca7e3f..d6e6724446c8 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -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. diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c index 18ae83dd1cd7..b56c65de384d 100644 --- a/arch/x86/kernel/vsyscall_64.c +++ b/arch/x86/kernel/vsyscall_64.c @@ -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) { -- 2.20.1