linux-kernel - [ 099/117] MCE: Fix vm86 handling for 32bit mce handler

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Date:	Mon, 28 May 2012 04:13:41 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Andi Kleen <andi@...stfloor.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Tony Luck <tony.luck@...el.com>
Subject: [ 099/117] MCE: Fix vm86 handling for 32bit mce handler

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andi Kleen <andi@...stfloor.org>

commit a129a7c84582629741e5fa6f40026efcd7a65bd4 upstream.

When running on 32bit the mce handler could misinterpret
vm86 mode as ring 0. This can affect whether it does recovery
or not; it was possible to panic when recovery was actually
possible.

Fix this by always forcing vm86 to look like ring 3.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Tony Luck <tony.luck@...el.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kernel/cpu/mcheck/mce.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 66e1c51..5f793e6 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -437,6 +437,14 @@ static inline void mce_gather_info(struct mce *m, struct pt_regs *regs)
 		if (m->mcgstatus & (MCG_STATUS_RIPV|MCG_STATUS_EIPV)) {
 			m->ip = regs->ip;
 			m->cs = regs->cs;
+
+			/*
+			 * When in VM86 mode make the cs look like ring 3
+			 * always. This is a lie, but it's better than passing
+			 * the additional vm86 bit around everywhere.
+			 */
+			if (v8086_mode(regs))
+				m->cs |= 3;
 		}
 		/* Use accurate RIP reporting if available. */
 		if (rip_msr)


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