Patch "x86, cpu, amd: Add workaround for family 16h, erratum 793" has been added to the 3.13-stable tree

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This is a note to let you know that I've just added the patch titled

    x86, cpu, amd: Add workaround for family 16h, erratum 793

to the 3.13-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-cpu-amd-add-workaround-for-family-16h-erratum-793.patch
and it can be found in the queue-3.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 3b56496865f9f7d9bcb2f93b44c63f274f08e3b6 Mon Sep 17 00:00:00 2001
From: Borislav Petkov <bp@xxxxxxx>
Date: Wed, 15 Jan 2014 00:07:11 +0100
Subject: x86, cpu, amd: Add workaround for family 16h, erratum 793

From: Borislav Petkov <bp@xxxxxxx>

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@xxxxxxx>
Link: http://lkml.kernel.org/r/20140114230711.GS29865@xxxxxxx
Tested-by: Aravind Gopalakrishnan <aravind.gopalakrishnan@xxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/x86/include/uapi/asm/msr-index.h |    1 +
 arch/x86/kernel/cpu/amd.c             |   10 ++++++++++
 2 files changed, 11 insertions(+)

--- a/arch/x86/include/uapi/asm/msr-index.h
+++ b/arch/x86/include/uapi/asm/msr-index.h
@@ -184,6 +184,7 @@
 #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_BU_CFG2		0xc001102a
 #define MSR_AMD64_IBSFETCHCTL		0xc0011030
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -508,6 +508,16 @@ static void early_init_amd(struct cpuinf
 			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;
+
+		rdmsrl(MSR_AMD64_LS_CFG, val);
+		if (!(val & BIT(15)))
+			wrmsrl(MSR_AMD64_LS_CFG, val | BIT(15));
+	}
+
 }
 
 static const int amd_erratum_383[];


Patches currently in stable-queue which might be from bp@xxxxxxx are

queue-3.13/x86-efi-fix-off-by-one-bug-in-efi-boot-services-reservation.patch
queue-3.13/rtc-cmos-add-an-alarm-disable-quirk.patch
queue-3.13/x86-cpu-amd-add-workaround-for-family-16h-erratum-793.patch
queue-3.13/e752x_edac-fix-pci_dev-usage-count.patch
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