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

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@suse.de>
Link: http://lkml.kernel.org/r/20140114230711.GS29865@pd.tnic
Tested-by: Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/uapi/asm/msr-index.h b/arch/x86/include/uapi/asm/msr-index.h
index 2af848dfa75424b7798924dd9a91524af7f088e3..d3fd447ecbeef26edc4eb79826c7f0c2d672a6c7 100644 (file)
--- a/arch/x86/include/uapi/asm/msr-index.h
+++ b/arch/x86/include/uapi/asm/msr-index.h
@@ -179,6 +179,7 @@
 #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

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 5013a48d1aff7a2f859a4d2e28224d1da4d95ea4..ae177a014180b5ad497cc274d2d04bfe593c13b2 100644 (file)
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -508,6 +508,16 @@ 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;
+
+               rdmsrl(MSR_AMD64_LS_CFG, val);
+               if (!(val & BIT(15)))
+                       wrmsrl(MSR_AMD64_LS_CFG, val | BIT(15));
+       }
+
 }
 
 static const int amd_erratum_383[];