[tip:x86/vdso] x86_64/vsyscall: Restore orig_ax after vsyscall seccomp

[tip-bot for Andy Lutomirski]

Commit-ID:  26893107aa717cd11010f0c278d02535defa1ac9
Gitweb:     http://git.kernel.org/tip/26893107aa717cd11010f0c278d02535defa1ac9
Author:     Andy Lutomirski <luto@xxxxxxxxxxxxxx>
AuthorDate: Tue, 4 Nov 2014 15:36:50 -0800
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 10 Nov 2014 10:46:35 +0100

x86_64/vsyscall: Restore orig_ax after vsyscall seccomp

The vsyscall emulation code sets orig_ax for seccomp's benefit,
but it forgot to set it back.

I'm not sure that this is observable at all, but it could cause
confusion to various /proc or ptrace users, and it's possible
that it could cause minor artifacts if a signal were to be
delivered on return from vsyscall emulation.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/cdc6a564517a4df09235572ee5f530ccdcf933f7.1415144089.git.luto@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/vsyscall_64.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 7d9eb4b..2dcc6ff 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -206,6 +206,7 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
 				  "seccomp tried to change syscall nr or ip");
 		do_exit(SIGSYS);
 	}
+	regs->orig_ax = -1;
 	if (tmp)
 		goto do_ret;  /* skip requested */
 
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