x86_64: Ignore compat mode SYSCALL when IA32_EMULATION is not defined

Previously a program could switch to a compat mode segment and then
execute SYSCALL and it would jump to an uninitialized MSR and crash
the kernel.

Instead supply a dummy target for this case.

Pointed out by Jan Beulich

Cc: jbeulich@novell.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index fa984b53e7e6..a67f87bf4015 100644
--- a/arch/x86_64/kernel/entry.S
+++ b/arch/x86_64/kernel/entry.S
@@ -1163,3 +1163,10 @@ ENTRY(call_softirq)
         ret
         CFI_ENDPROC
 ENDPROC(call_softirq)
+
+KPROBE_ENTRY(ignore_sysret)
+        CFI_STARTPROC
+        mov $-ENOSYS,%eax
+        sysret
+        CFI_ENDPROC
+ENDPROC(ignore_sysret)