x86: Default to vsyscall=native for now
Adrian Bunk [Wed, 5 Oct 2011 21:40:47 +0000 (00:40 +0300)]
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>

Documentation/kernel-parameters.txt
arch/x86/kernel/vsyscall_64.c

index 854ed5c..d6e6724 100644 (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.
index 18ae83d..b56c65d 100644 (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)
 {