linux-kernel - [PATCH] x86/entry/compat: Add missing CLAC to entry_INT80

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Message-Id: <b02b7e71ae54074be01fc171cbd4b72517055c0e.1456345086.git.luto@kernel.org>
Date:	Wed, 24 Feb 2016 12:18:49 -0800
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org
Cc:	Brian Gerst <brgerst@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>, stable@...r.kernel.org
Subject: [PATCH] x86/entry/compat: Add missing CLAC to entry_INT80_32

This doesn't seem to fix a regression -- I don't think the CLAC was
ever there.

I double-checked in a debugger: entries through the int80 gate do
not automatically clear AC.

Stable maintainers: I can provide a backport to 4.3 and earlier if
needed.  This needs to be backported all the way to 3.10.

Reported-by: Brian Gerst <brgerst@...il.com>
Cc: stable@...r.kernel.org
Fixes: 63bcff2a307b ("x86, smap: Add STAC and CLAC instructions to control user space access")
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/entry/entry_64_compat.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 5e887ee35662..41fbb3389a2f 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -261,6 +261,7 @@ ENTRY(entry_INT80_compat)
 	 * Interrupts are off on entry.
 	 */
 	PARAVIRT_ADJUST_EXCEPTION_FRAME
+	ASM_CLAC			/* Do this early to minimize exposure */
 	SWAPGS
 
 	/*
-- 
2.5.0