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 d1b11b4c40d28b78a4c7a64a802dbb1f0da73727..75d2218cd0328c87efd9f102a8be050530ff716c 100644 (file)
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -669,6 +669,9 @@
 #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 86059f2c0fcd45c0405e7f623d86769c4c90f79f..b3499c84d89dd816c8aab65960cb093e434ab44b 100644 (file)
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -949,6 +949,9 @@ static void init_amd_zen1(struct cpuinfo_x86 *c)
                msr_clear_bit(MSR_K7_HWCR, MSR_K7_HWCR_IRPERF_EN_BIT);
                clear_cpu_cap(c, X86_FEATURE_IRPERF);
        }
+
+       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 const struct x86_cpu_id amd_zenbleed_microcode[] = {