x86/CPU: Fix FPDSS on Zen1

commit e55d98e7756135f32150b9b8f75d580d0d4b2dd3 upstream.

Zen1's hardware divider can leave, under certain circumstances, partial
results from previous operations.  Those results can be leaked by
another, attacker thread.

Fix that with a chicken bit.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 749e7fe245e6579546b187d2948391dc48992e77..5b8268afc0358c89e0d83ef7ad9a3c6a98fcb740 100644 (file)
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -580,6 +580,9 @@
 #define MSR_AMD64_DC_CFG               0xc0011022
 #define MSR_AMD64_TW_CFG               0xc0011023
 
+#define MSR_AMD64_FP_CFG               0xc0011028
+#define MSR_AMD64_FP_CFG_ZEN1_DENORM_FIX_BIT   9
+
 #define MSR_AMD64_DE_CFG               0xc0011029
 #define MSR_AMD64_DE_CFG_LFENCE_SERIALIZE_BIT   1
 #define MSR_AMD64_DE_CFG_LFENCE_SERIALIZE      BIT_ULL(MSR_AMD64_DE_CFG_LFENCE_SERIALIZE_BIT)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 2d71c329b3475c1eb072ded8802d9bec43ba99f5..1ba9fcfde6d20cb276cd5ebb4145d01c4367ec36 100644 (file)
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1051,6 +1051,9 @@ static void init_amd_zn(struct cpuinfo_x86 *c)
                if (c->x86 == 0x19 && !cpu_has(c, X86_FEATURE_BTC_NO))
                        set_cpu_cap(c, X86_FEATURE_BTC_NO);
        }
+
+       pr_notice_once("AMD Zen1 FPDSS bug detected, enabling mitigation.\n");
+       msr_set_bit(MSR_AMD64_FP_CFG, MSR_AMD64_FP_CFG_ZEN1_DENORM_FIX_BIT);
 }
 
 static bool cpu_has_zenbleed_microcode(void)