From: Andi Kleen ak@linux.intel.com
commit ed5194c2732c8084af9fd159c146ea92bf137128 upstream.
Microarchitectural Data Sampling (MDS), is a class of side channel attacks on internal buffers in Intel CPUs. The variants are:
- Microarchitectural Store Buffer Data Sampling (MSBDS) (CVE-2018-12126) - Microarchitectural Fill Buffer Data Sampling (MFBDS) (CVE-2018-12130) - Microarchitectural Load Port Data Sampling (MLPDS) (CVE-2018-12127)
MSBDS leaks Store Buffer Entries which can be speculatively forwarded to a dependent load (store-to-load forwarding) as an optimization. The forward can also happen to a faulting or assisting load operation for a different memory address, which can be exploited under certain conditions. Store buffers are partitioned between Hyper-Threads so cross thread forwarding is not possible. But if a thread enters or exits a sleep state the store buffer is repartitioned which can expose data from one thread to the other.
MFBDS leaks Fill Buffer Entries. Fill buffers are used internally to manage L1 miss situations and to hold data which is returned or sent in response to a memory or I/O operation. Fill buffers can forward data to a load operation and also write data to the cache. When the fill buffer is deallocated it can retain the stale data of the preceding operations which can then be forwarded to a faulting or assisting load operation, which can be exploited under certain conditions. Fill buffers are shared between Hyper-Threads so cross thread leakage is possible.
MLDPS leaks Load Port Data. Load ports are used to perform load operations from memory or I/O. The received data is then forwarded to the register file or a subsequent operation. In some implementations the Load Port can contain stale data from a previous operation which can be forwarded to faulting or assisting loads under certain conditions, which again can be exploited eventually. Load ports are shared between Hyper-Threads so cross thread leakage is possible.
All variants have the same mitigation for single CPU thread case (SMT off), so the kernel can treat them as one MDS issue.
Add the basic infrastructure to detect if the current CPU is affected by MDS.
[ tglx: Rewrote changelog ]
Signed-off-by: Andi Kleen ak@linux.intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Borislav Petkov bp@suse.de Reviewed-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Reviewed-by: Frederic Weisbecker frederic@kernel.org Reviewed-by: Jon Masters jcm@redhat.com Tested-by: Jon Masters jcm@redhat.com [bwh: Backported to 4.4: adjust context, indentation] Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/cpufeatures.h | 2 ++ arch/x86/include/asm/msr-index.h | 5 +++++ arch/x86/kernel/cpu/common.c | 25 ++++++++++++++++--------- 3 files changed, 23 insertions(+), 9 deletions(-)
--- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -310,6 +310,7 @@ /* Intel-defined CPU features, CPUID level 0x00000007:0 (EDX), word 18 */ #define X86_FEATURE_AVX512_4VNNIW (18*32+ 2) /* AVX-512 Neural Network Instructions */ #define X86_FEATURE_AVX512_4FMAPS (18*32+ 3) /* AVX-512 Multiply Accumulation Single precision */ +#define X86_FEATURE_MD_CLEAR (18*32+10) /* VERW clears CPU buffers */ #define X86_FEATURE_SPEC_CTRL (18*32+26) /* "" Speculation Control (IBRS + IBPB) */ #define X86_FEATURE_INTEL_STIBP (18*32+27) /* "" Single Thread Indirect Branch Predictors */ #define X86_FEATURE_FLUSH_L1D (18*32+28) /* Flush L1D cache */ @@ -335,5 +336,6 @@ #define X86_BUG_SPECTRE_V2 X86_BUG(16) /* CPU is affected by Spectre variant 2 attack with indirect branches */ #define X86_BUG_SPEC_STORE_BYPASS X86_BUG(17) /* CPU is affected by speculative store bypass attack */ #define X86_BUG_L1TF X86_BUG(18) /* CPU is affected by L1 Terminal Fault */ +#define X86_BUG_MDS X86_BUG(19) /* CPU is affected by Microarchitectural data sampling */
#endif /* _ASM_X86_CPUFEATURES_H */ --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -66,6 +66,11 @@ * attack, so no Speculative Store Bypass * control required. */ +#define ARCH_CAP_MDS_NO BIT(5) /* + * Not susceptible to + * Microarchitectural Data + * Sampling (MDS) vulnerabilities. + */
#define MSR_IA32_BBL_CR_CTL 0x00000119 #define MSR_IA32_BBL_CR_CTL3 0x0000011e --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -851,6 +851,7 @@ static void identify_cpu_without_cpuid(s #define NO_MELTDOWN BIT(1) #define NO_SSB BIT(2) #define NO_L1TF BIT(3) +#define NO_MDS BIT(4)
#define VULNWL(_vendor, _family, _model, _whitelist) \ { X86_VENDOR_##_vendor, _family, _model, X86_FEATURE_ANY, _whitelist } @@ -867,6 +868,7 @@ static const __initconst struct x86_cpu_ VULNWL(INTEL, 5, X86_MODEL_ANY, NO_SPECULATION), VULNWL(NSC, 5, X86_MODEL_ANY, NO_SPECULATION),
+ /* Intel Family 6 */ VULNWL_INTEL(ATOM_SALTWELL, NO_SPECULATION), VULNWL_INTEL(ATOM_SALTWELL_TABLET, NO_SPECULATION), VULNWL_INTEL(ATOM_SALTWELL_MID, NO_SPECULATION), @@ -883,17 +885,19 @@ static const __initconst struct x86_cpu_ VULNWL_INTEL(CORE_YONAH, NO_SSB),
VULNWL_INTEL(ATOM_AIRMONT_MID, NO_L1TF), - VULNWL_INTEL(ATOM_GOLDMONT, NO_L1TF), - VULNWL_INTEL(ATOM_GOLDMONT_X, NO_L1TF), - VULNWL_INTEL(ATOM_GOLDMONT_PLUS, NO_L1TF), - - VULNWL_AMD(0x0f, NO_MELTDOWN | NO_SSB | NO_L1TF), - VULNWL_AMD(0x10, NO_MELTDOWN | NO_SSB | NO_L1TF), - VULNWL_AMD(0x11, NO_MELTDOWN | NO_SSB | NO_L1TF), - VULNWL_AMD(0x12, NO_MELTDOWN | NO_SSB | NO_L1TF), + + VULNWL_INTEL(ATOM_GOLDMONT, NO_MDS | NO_L1TF), + VULNWL_INTEL(ATOM_GOLDMONT_X, NO_MDS | NO_L1TF), + VULNWL_INTEL(ATOM_GOLDMONT_PLUS, NO_MDS | NO_L1TF), + + /* AMD Family 0xf - 0x12 */ + VULNWL_AMD(0x0f, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS), + VULNWL_AMD(0x10, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS), + VULNWL_AMD(0x11, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS), + VULNWL_AMD(0x12, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS),
/* FAMILY_ANY must be last, otherwise 0x0f - 0x12 matches won't work */ - VULNWL_AMD(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF), + VULNWL_AMD(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF | NO_MDS), {} };
@@ -924,6 +928,9 @@ static void __init cpu_set_bug_bits(stru if (ia32_cap & ARCH_CAP_IBRS_ALL) setup_force_cpu_cap(X86_FEATURE_IBRS_ENHANCED);
+ if (!cpu_matches(NO_MDS) && !(ia32_cap & ARCH_CAP_MDS_NO)) + setup_force_cpu_bug(X86_BUG_MDS); + if (cpu_matches(NO_MELTDOWN)) return;