[tip:x86/asm] x86/asm/64: Clear AC on NMI entries

[tip-bot for Andy Lutomirski]

Commit-ID:  e93c17301ac55321fc18e0f8316e924e58a83c8c
Gitweb:     http://git.kernel.org/tip/e93c17301ac55321fc18e0f8316e924e58a83c8c
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Mon, 7 Aug 2017 19:43:13 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 10 Aug 2017 13:13:15 +0200

x86/asm/64: Clear AC on NMI entries

This closes a hole in our SMAP implementation.

This patch comes from grsecurity. Good catch!

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/314cc9f294e8f14ed85485727556ad4f15bb1659.1502159503.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/entry/entry_64.S | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index d271fb7..6d078b8 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1211,6 +1211,8 @@ ENTRY(nmi)
 	 * other IST entries.
 	 */
 
+	ASM_CLAC
+
 	/* Use %rdx as our temp variable throughout */
 	pushq	%rdx