linux-kernel - [ 11/48] x86, cpu, amd: Add workaround for family 16h, erratum 793

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Message-Id: <20150515080530.764459086@1wt.eu>
Date:	Fri, 15 May 2015 10:05:41 +0200
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Borislav Petkov <bp@...e.de>,
	Aravind Gopalakrishnan <aravind.gopalakrishnan@....com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>, Willy Tarreau <w@....eu>
Subject: [ 11/48] x86, cpu, amd: Add workaround for family 16h, erratum
 793

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

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

From: Borislav Petkov <bp@...e.de>

commit 3b56496865f9f7d9bcb2f93b44c63f274f08e3b6 upstream

This adds the workaround for erratum 793 as a precaution in case not
every BIOS implements it.  This addresses CVE-2013-6885.

Erratum text:

[Revision Guide for AMD Family 16h Models 00h-0Fh Processors,
document 51810 Rev. 3.04 November 2013]

793 Specific Combination of Writes to Write Combined Memory Types and
Locked Instructions May Cause Core Hang

Description

Under a highly specific and detailed set of internal timing
conditions, a locked instruction may trigger a timing sequence whereby
the write to a write combined memory type is not flushed, causing the
locked instruction to stall indefinitely.

Potential Effect on System

Processor core hang.

Suggested Workaround

BIOS should set MSR
C001_1020[15] = 1b.

Fix Planned

No fix planned

[ hpa: updated description, fixed typo in MSR name ]

Signed-off-by: Borislav Petkov <bp@...e.de>
Link: http://lkml.kernel.org/r/20140114230711.GS29865@pd.tnic
Tested-by: Aravind Gopalakrishnan <aravind.gopalakrishnan@....com>
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
[bwh: Backported to 3.2:
 - Adjust filename
 - Venkatesh Srinivas pointed out we should use {rd,wr}msrl_safe() to
   avoid crashing on KVM.  This was fixed upstream by commit 8f86a7373a1c
   ("x86, AMD: Convert to the new bit access MSR accessors") but that's too
   much trouble to backport.  Here we must use {rd,wr}msrl_amd_safe().]
Signed-off-by: Willy Tarreau <w@....eu>
---
 arch/x86/include/asm/msr-index.h |  1 +
 arch/x86/kernel/cpu/amd.c        | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 883037b..6057b70 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -110,6 +110,7 @@
 #define MSR_AMD64_PATCH_LOADER		0xc0010020
 #define MSR_AMD64_OSVW_ID_LENGTH	0xc0010140
 #define MSR_AMD64_OSVW_STATUS		0xc0010141
+#define MSR_AMD64_LS_CFG		0xc0011020
 #define MSR_AMD64_DC_CFG		0xc0011022
 #define MSR_AMD64_IBSFETCHCTL		0xc0011030
 #define MSR_AMD64_IBSFETCHLINAD		0xc0011031
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 6e082dc..ae8b02c 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -413,6 +413,16 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
 			set_cpu_cap(c, X86_FEATURE_EXTD_APICID);
 	}
 #endif
+
+	/* F16h erratum 793, CVE-2013-6885 */
+	if (c->x86 == 0x16 && c->x86_model <= 0xf) {
+		u64 val;
+
+		if (!rdmsrl_amd_safe(MSR_AMD64_LS_CFG, &val) &&
+		    !(val & BIT(15)))
+			wrmsrl_amd_safe(MSR_AMD64_LS_CFG, val | BIT(15));
+	}
+
 }
 
 static void __cpuinit init_amd(struct cpuinfo_x86 *c)
-- 
1.7.12.2.21.g234cd45.dirty



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