[PATCH] x86_64,vsyscall: Restore orig_ax after vsyscall seccomp

[Andy Lutomirski]

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>
---

I misplaced this somehow as part of my vsyscall series.  It's very minor,
so I don't care much whether it makes 3.19.

My vsyscall seccomp tests all pass with or without this change.

 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 7d9eb4bc10ac..2dcc6ff6fdcc 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 */
 
-- 
1.9.3

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