linux-kernel - [PATCH 3/4] x86: call verify_cpu during 32bit CPU startup

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Message-ID: <20101109221843.GA5876@outflux.net>
Date:	Tue, 9 Nov 2010 14:18:43 -0800
From:	Kees Cook <kees.cook@...onical.com>
To:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/4] x86: call verify_cpu during 32bit CPU startup

The XD_DISABLE-clearing side-effect needs to happen for both 32bit
and 64bit, but the 32bit init routines were not calling verify_cpu()
yet. This adds that call to gain the side-effect.

The longmode/SSE tests being performed in verify_cpu() need to happen very
early for 64bit but not for 32bit. Instead of including it in two places
for 32bit, we can just include it once in arch/x86/kernel/head_32.S.

Signed-off-by: Kees Cook <kees.cook@...onical.com>
Acked-by: Pekka Enberg <penberg@...nel.org>
---
 arch/x86/kernel/head_32.S    |    6 ++++++
 arch/x86/kernel/verify_cpu.S |    1 +
 2 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index bcece91..fdaea52 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -314,6 +314,10 @@ ENTRY(startup_32_smp)
 	subl $0x80000001, %eax
 	cmpl $(0x8000ffff-0x80000001), %eax
 	ja 6f
+
+	/* Clear bogus XD_DISABLE bits */
+	call verify_cpu
+
 	mov $0x80000001, %eax
 	cpuid
 	/* Execute Disable bit supported? */
@@ -609,6 +613,8 @@ ignore_int:
 #endif
 	iret
 
+#include "verify_cpu.S"
+
 	__REFDATA
 .align 4
 ENTRY(initial_code)
diff --git a/arch/x86/kernel/verify_cpu.S b/arch/x86/kernel/verify_cpu.S
index ccb4136..5644b4b 100644
--- a/arch/x86/kernel/verify_cpu.S
+++ b/arch/x86/kernel/verify_cpu.S
@@ -19,6 +19,7 @@
  *
  *	arch/x86_64/boot/compressed/head_64.S: Boot cpu verification
  *	arch/x86_64/kernel/trampoline_64.S: secondary processor verfication
+ *	arch/x86_64/kernel/head_32.S: processor startup
  *
  *	verify_cpu, returns the status of longmode and SSE in register %eax.
  *		0: Success    1: Failure
-- 
1.7.2.3


-- 
Kees Cook
Ubuntu Security Team
--
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