diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2019-05-14 07:57:29 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-05-14 07:57:29 -0700 |
commit | fa4bff165070dc40a3de35b78e4f8da8e8d85ec5 (patch) | |
tree | 1430bdefedcf00030b4152baf12f530a04bd25f3 /arch/x86/include/asm | |
parent | 63863ee8e2f6f6ae47be3dff4af2f2806f5ca2dd (diff) | |
parent | 95310e348a321b45fb746c176961d4da72344282 (diff) |
Merge branch 'x86-mds-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 MDS mitigations from Thomas Gleixner:
"Microarchitectural Data Sampling (MDS) is a hardware vulnerability
which allows unprivileged speculative access to data which is
available in various CPU internal buffers. This new set of misfeatures
has the following CVEs assigned:
CVE-2018-12126 MSBDS Microarchitectural Store Buffer Data Sampling
CVE-2018-12130 MFBDS Microarchitectural Fill Buffer Data Sampling
CVE-2018-12127 MLPDS Microarchitectural Load Port Data Sampling
CVE-2019-11091 MDSUM Microarchitectural Data Sampling Uncacheable Memory
MDS attacks target microarchitectural buffers which speculatively
forward data under certain conditions. Disclosure gadgets can expose
this data via cache side channels.
Contrary to other speculation based vulnerabilities the MDS
vulnerability does not allow the attacker to control the memory target
address. As a consequence the attacks are purely sampling based, but
as demonstrated with the TLBleed attack samples can be postprocessed
successfully.
The mitigation is to flush the microarchitectural buffers on return to
user space and before entering a VM. It's bolted on the VERW
instruction and requires a microcode update. As some of the attacks
exploit data structures shared between hyperthreads, full protection
requires to disable hyperthreading. The kernel does not do that by
default to avoid breaking unattended updates.
The mitigation set comes with documentation for administrators and a
deeper technical view"
* 'x86-mds-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (23 commits)
x86/speculation/mds: Fix documentation typo
Documentation: Correct the possible MDS sysfs values
x86/mds: Add MDSUM variant to the MDS documentation
x86/speculation/mds: Add 'mitigations=' support for MDS
x86/speculation/mds: Print SMT vulnerable on MSBDS with mitigations off
x86/speculation/mds: Fix comment
x86/speculation/mds: Add SMT warning message
x86/speculation: Move arch_smt_update() call to after mitigation decisions
x86/speculation/mds: Add mds=full,nosmt cmdline option
Documentation: Add MDS vulnerability documentation
Documentation: Move L1TF to separate directory
x86/speculation/mds: Add mitigation mode VMWERV
x86/speculation/mds: Add sysfs reporting for MDS
x86/speculation/mds: Add mitigation control for MDS
x86/speculation/mds: Conditionally clear CPU buffers on idle entry
x86/kvm/vmx: Add MDS protection when L1D Flush is not active
x86/speculation/mds: Clear CPU buffers on exit to user
x86/speculation/mds: Add mds_clear_cpu_buffers()
x86/kvm: Expose X86_FEATURE_MD_CLEAR to guests
x86/speculation/mds: Add BUG_MSBDS_ONLY
...
Diffstat (limited to 'arch/x86/include/asm')
-rw-r--r-- | arch/x86/include/asm/cpufeatures.h | 3 | ||||
-rw-r--r-- | arch/x86/include/asm/irqflags.h | 4 | ||||
-rw-r--r-- | arch/x86/include/asm/msr-index.h | 39 | ||||
-rw-r--r-- | arch/x86/include/asm/mwait.h | 7 | ||||
-rw-r--r-- | arch/x86/include/asm/nospec-branch.h | 50 | ||||
-rw-r--r-- | arch/x86/include/asm/processor.h | 6 |
6 files changed, 93 insertions, 16 deletions
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index 981ff9479648..75f27ee2c263 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -344,6 +344,7 @@ /* 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_TSX_FORCE_ABORT (18*32+13) /* "" TSX_FORCE_ABORT */ #define X86_FEATURE_PCONFIG (18*32+18) /* Intel PCONFIG */ #define X86_FEATURE_SPEC_CTRL (18*32+26) /* "" Speculation Control (IBRS + IBPB) */ @@ -382,5 +383,7 @@ #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 */ +#define X86_BUG_MSBDS_ONLY X86_BUG(20) /* CPU is only affected by the MSDBS variant of BUG_MDS */ #endif /* _ASM_X86_CPUFEATURES_H */ diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h index 058e40fed167..8a0e56e1dcc9 100644 --- a/arch/x86/include/asm/irqflags.h +++ b/arch/x86/include/asm/irqflags.h @@ -6,6 +6,8 @@ #ifndef __ASSEMBLY__ +#include <asm/nospec-branch.h> + /* Provide __cpuidle; we can't safely include <linux/cpu.h> */ #define __cpuidle __attribute__((__section__(".cpuidle.text"))) @@ -54,11 +56,13 @@ static inline void native_irq_enable(void) static inline __cpuidle void native_safe_halt(void) { + mds_idle_clear_cpu_buffers(); asm volatile("sti; hlt": : :"memory"); } static inline __cpuidle void native_halt(void) { + mds_idle_clear_cpu_buffers(); asm volatile("hlt": : :"memory"); } diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h index 1378518cf63f..88dd202c8b00 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -2,6 +2,8 @@ #ifndef _ASM_X86_MSR_INDEX_H #define _ASM_X86_MSR_INDEX_H +#include <linux/bits.h> + /* * CPU model specific register (MSR) numbers. * @@ -40,14 +42,14 @@ /* Intel MSRs. Some also available on other CPUs */ #define MSR_IA32_SPEC_CTRL 0x00000048 /* Speculation Control */ -#define SPEC_CTRL_IBRS (1 << 0) /* Indirect Branch Restricted Speculation */ +#define SPEC_CTRL_IBRS BIT(0) /* Indirect Branch Restricted Speculation */ #define SPEC_CTRL_STIBP_SHIFT 1 /* Single Thread Indirect Branch Predictor (STIBP) bit */ -#define SPEC_CTRL_STIBP (1 << SPEC_CTRL_STIBP_SHIFT) /* STIBP mask */ +#define SPEC_CTRL_STIBP BIT(SPEC_CTRL_STIBP_SHIFT) /* STIBP mask */ #define SPEC_CTRL_SSBD_SHIFT 2 /* Speculative Store Bypass Disable bit */ -#define SPEC_CTRL_SSBD (1 << SPEC_CTRL_SSBD_SHIFT) /* Speculative Store Bypass Disable */ +#define SPEC_CTRL_SSBD BIT(SPEC_CTRL_SSBD_SHIFT) /* Speculative Store Bypass Disable */ #define MSR_IA32_PRED_CMD 0x00000049 /* Prediction Command */ -#define PRED_CMD_IBPB (1 << 0) /* Indirect Branch Prediction Barrier */ +#define PRED_CMD_IBPB BIT(0) /* Indirect Branch Prediction Barrier */ #define MSR_PPIN_CTL 0x0000004e #define MSR_PPIN 0x0000004f @@ -69,20 +71,25 @@ #define MSR_MTRRcap 0x000000fe #define MSR_IA32_ARCH_CAPABILITIES 0x0000010a -#define ARCH_CAP_RDCL_NO (1 << 0) /* Not susceptible to Meltdown */ -#define ARCH_CAP_IBRS_ALL (1 << 1) /* Enhanced IBRS support */ -#define ARCH_CAP_SKIP_VMENTRY_L1DFLUSH (1 << 3) /* Skip L1D flush on vmentry */ -#define ARCH_CAP_SSB_NO (1 << 4) /* - * Not susceptible to Speculative Store Bypass - * attack, so no Speculative Store Bypass - * control required. - */ +#define ARCH_CAP_RDCL_NO BIT(0) /* Not susceptible to Meltdown */ +#define ARCH_CAP_IBRS_ALL BIT(1) /* Enhanced IBRS support */ +#define ARCH_CAP_SKIP_VMENTRY_L1DFLUSH BIT(3) /* Skip L1D flush on vmentry */ +#define ARCH_CAP_SSB_NO BIT(4) /* + * Not susceptible to Speculative Store Bypass + * 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_FLUSH_CMD 0x0000010b -#define L1D_FLUSH (1 << 0) /* - * Writeback and invalidate the - * L1 data cache. - */ +#define L1D_FLUSH BIT(0) /* + * Writeback and invalidate the + * L1 data cache. + */ #define MSR_IA32_BBL_CR_CTL 0x00000119 #define MSR_IA32_BBL_CR_CTL3 0x0000011e diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h index 39a2fb29378a..eb0f80ce8524 100644 --- a/arch/x86/include/asm/mwait.h +++ b/arch/x86/include/asm/mwait.h @@ -6,6 +6,7 @@ #include <linux/sched/idle.h> #include <asm/cpufeature.h> +#include <asm/nospec-branch.h> #define MWAIT_SUBSTATE_MASK 0xf #define MWAIT_CSTATE_MASK 0xf @@ -40,6 +41,8 @@ static inline void __monitorx(const void *eax, unsigned long ecx, static inline void __mwait(unsigned long eax, unsigned long ecx) { + mds_idle_clear_cpu_buffers(); + /* "mwait %eax, %ecx;" */ asm volatile(".byte 0x0f, 0x01, 0xc9;" :: "a" (eax), "c" (ecx)); @@ -74,6 +77,8 @@ static inline void __mwait(unsigned long eax, unsigned long ecx) static inline void __mwaitx(unsigned long eax, unsigned long ebx, unsigned long ecx) { + /* No MDS buffer clear as this is AMD/HYGON only */ + /* "mwaitx %eax, %ebx, %ecx;" */ asm volatile(".byte 0x0f, 0x01, 0xfb;" :: "a" (eax), "b" (ebx), "c" (ecx)); @@ -81,6 +86,8 @@ static inline void __mwaitx(unsigned long eax, unsigned long ebx, static inline void __sti_mwait(unsigned long eax, unsigned long ecx) { + mds_idle_clear_cpu_buffers(); + trace_hardirqs_on(); /* "mwait %eax, %ecx;" */ asm volatile("sti; .byte 0x0f, 0x01, 0xc9;" diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index daf25b60c9e3..109f974f9835 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -308,6 +308,56 @@ DECLARE_STATIC_KEY_FALSE(switch_to_cond_stibp); DECLARE_STATIC_KEY_FALSE(switch_mm_cond_ibpb); DECLARE_STATIC_KEY_FALSE(switch_mm_always_ibpb); +DECLARE_STATIC_KEY_FALSE(mds_user_clear); +DECLARE_STATIC_KEY_FALSE(mds_idle_clear); + +#include <asm/segment.h> + +/** + * mds_clear_cpu_buffers - Mitigation for MDS vulnerability + * + * This uses the otherwise unused and obsolete VERW instruction in + * combination with microcode which triggers a CPU buffer flush when the + * instruction is executed. + */ +static inline void mds_clear_cpu_buffers(void) +{ + static const u16 ds = __KERNEL_DS; + + /* + * Has to be the memory-operand variant because only that + * guarantees the CPU buffer flush functionality according to + * documentation. The register-operand variant does not. + * Works with any segment selector, but a valid writable + * data segment is the fastest variant. + * + * "cc" clobber is required because VERW modifies ZF. + */ + asm volatile("verw %[ds]" : : [ds] "m" (ds) : "cc"); +} + +/** + * mds_user_clear_cpu_buffers - Mitigation for MDS vulnerability + * + * Clear CPU buffers if the corresponding static key is enabled + */ +static inline void mds_user_clear_cpu_buffers(void) +{ + if (static_branch_likely(&mds_user_clear)) + mds_clear_cpu_buffers(); +} + +/** + * mds_idle_clear_cpu_buffers - Mitigation for MDS vulnerability + * + * Clear CPU buffers if the corresponding static key is enabled + */ +static inline void mds_idle_clear_cpu_buffers(void) +{ + if (static_branch_likely(&mds_idle_clear)) + mds_clear_cpu_buffers(); +} + #endif /* __ASSEMBLY__ */ /* diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 7e99ef67bff0..c34a35c78618 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -978,4 +978,10 @@ enum l1tf_mitigations { extern enum l1tf_mitigations l1tf_mitigation; +enum mds_mitigations { + MDS_MITIGATION_OFF, + MDS_MITIGATION_FULL, + MDS_MITIGATION_VMWERV, +}; + #endif /* _ASM_X86_PROCESSOR_H */ |