From: Konrad Rzeszutek Wilk konrad.wilk@oracle.com
commit 6ac2f49edb1ef5446089c7c660017732886d62d6 upstream.
The AMD document outlining the SSBD handling 124441_AMD64_SpeculativeStoreBypassDisable_Whitepaper_final.pdf mentions that if CPUID 8000_0008.EBX[24] is set we should be using the SPEC_CTRL MSR (0x48) over the VIRT SPEC_CTRL MSR (0xC001_011f) for speculative store bypass disable.
This in effect means we should clear the X86_FEATURE_VIRT_SSBD flag so that we would prefer the SPEC_CTRL MSR.
See the document titled: 124441_AMD64_SpeculativeStoreBypassDisable_Whitepaper_final.pdf
A copy of this document is available at https://bugzilla.kernel.org/show_bug.cgi?id=199889
Signed-off-by: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: Tom Lendacky thomas.lendacky@amd.com Cc: Janakarajan Natarajan Janakarajan.Natarajan@amd.com Cc: kvm@vger.kernel.org Cc: KarimAllah Ahmed karahmed@amazon.de Cc: andrew.cooper3@citrix.com Cc: Joerg Roedel joro@8bytes.org Cc: Radim Krčmář rkrcmar@redhat.com Cc: Andy Lutomirski luto@kernel.org Cc: "H. Peter Anvin" hpa@zytor.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: Borislav Petkov bp@suse.de Cc: David Woodhouse dwmw@amazon.co.uk Cc: Kees Cook keescook@chromium.org Link: https://lkml.kernel.org/r/20180601145921.9500-3-konrad.wilk@oracle.com [bwh: Backported to 4.4: - Update feature test in guest_cpuid_has_spec_ctrl() instead of svm_{get,set}_msr() - 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 | 1 + arch/x86/kernel/cpu/bugs.c | 12 +++++++----- arch/x86/kernel/cpu/common.c | 6 ++++++ arch/x86/kvm/cpuid.c | 10 ++++++++-- arch/x86/kvm/cpuid.h | 2 +- arch/x86/kvm/svm.c | 2 +- 6 files changed, 24 insertions(+), 9 deletions(-)
--- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -269,6 +269,7 @@ #define X86_FEATURE_AMD_IBPB (13*32+12) /* "" Indirect Branch Prediction Barrier */ #define X86_FEATURE_AMD_IBRS (13*32+14) /* "" Indirect Branch Restricted Speculation */ #define X86_FEATURE_AMD_STIBP (13*32+15) /* "" Single Thread Indirect Branch Predictors */ +#define X86_FEATURE_AMD_SSBD (13*32+24) /* "" Speculative Store Bypass Disable */ #define X86_FEATURE_VIRT_SSBD (13*32+25) /* Virtualized Speculative Store Bypass Disable */ #define X86_FEATURE_AMD_SSB_NO (13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
--- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -523,18 +523,20 @@ static enum ssb_mitigation __init __ssb_ if (mode == SPEC_STORE_BYPASS_DISABLE) { setup_force_cpu_cap(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE); /* - * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD uses - * a completely different MSR and bit dependent on family. + * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD may + * use a completely different MSR and bit dependent on family. */ switch (boot_cpu_data.x86_vendor) { case X86_VENDOR_INTEL: + case X86_VENDOR_AMD: + if (!static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) { + x86_amd_ssb_disable(); + break; + } x86_spec_ctrl_base |= SPEC_CTRL_SSBD; x86_spec_ctrl_mask |= SPEC_CTRL_SSBD; wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); break; - case X86_VENDOR_AMD: - x86_amd_ssb_disable(); - break; } }
--- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -709,6 +709,12 @@ static void init_speculation_control(str set_cpu_cap(c, X86_FEATURE_STIBP); set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL); } + + if (cpu_has(c, X86_FEATURE_AMD_SSBD)) { + set_cpu_cap(c, X86_FEATURE_SSBD); + set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL); + clear_cpu_cap(c, X86_FEATURE_VIRT_SSBD); + } }
void get_cpu_cap(struct cpuinfo_x86 *c) --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -343,7 +343,8 @@ static inline int __do_cpuid_ent(struct
/* cpuid 0x80000008.ebx */ const u32 kvm_cpuid_8000_0008_ebx_x86_features = - F(AMD_IBPB) | F(AMD_IBRS) | F(VIRT_SSBD) | F(AMD_SSB_NO); + F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) | + F(AMD_SSB_NO);
/* cpuid 0xC0000001.edx */ const u32 kvm_supported_word5_x86_features = @@ -607,7 +608,12 @@ static inline int __do_cpuid_ent(struct entry->ebx |= F(VIRT_SSBD); entry->ebx &= kvm_cpuid_8000_0008_ebx_x86_features; cpuid_mask(&entry->ebx, CPUID_8000_0008_EBX); - if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD)) + /* + * The preference is to use SPEC CTRL MSR instead of the + * VIRT_SPEC MSR. + */ + if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) && + !boot_cpu_has(X86_FEATURE_AMD_SSBD)) entry->ebx |= F(VIRT_SSBD); break; } --- a/arch/x86/kvm/cpuid.h +++ b/arch/x86/kvm/cpuid.h @@ -175,7 +175,7 @@ static inline bool guest_cpuid_has_spec_ struct kvm_cpuid_entry2 *best;
best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0); - if (best && (best->ebx & bit(X86_FEATURE_AMD_IBRS))) + if (best && (best->ebx & (bit(X86_FEATURE_AMD_IBRS | bit(X86_FEATURE_AMD_SSBD))))) return true; best = kvm_find_cpuid_entry(vcpu, 7, 0); return best && (best->edx & (bit(X86_FEATURE_SPEC_CTRL) | bit(X86_FEATURE_SPEC_CTRL_SSBD))); --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -3197,7 +3197,7 @@ static int svm_set_msr(struct kvm_vcpu * return 1;
/* The STIBP bit doesn't fault even if it's not advertised */ - if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP)) + if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD)) return 1;
svm->spec_ctrl = data;