* [PATCH v2 0/1] KVM: x86: Propagate AMD-specific IBRS bits to guests @ 2023-03-01 18:58 Takahiro Itazuri 2023-03-01 18:58 ` [PATCH v2 1/1] " Takahiro Itazuri 0 siblings, 1 reply; 4+ messages in thread From: Takahiro Itazuri @ 2023-03-01 18:58 UTC (permalink / raw) To: kvm, Sean Christopherson, Paolo Bonzini Cc: linux-kernel, Takahiro Itazuri, Takahiro Itazuri Changes since v2: * Move feature bits macros from arch/x86/include/asm/cpufeatures.h to arch/x86/kvm/reverse_cpuid.h. Takahiro Itazuri (1): KVM: x86: Propagate AMD-specific IBRS bits to guests arch/x86/kvm/cpuid.c | 5 +++-- arch/x86/kvm/reverse_cpuid.h | 5 +++++ 2 files changed, 8 insertions(+), 2 deletions(-) -- 2.38.0 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH v2 1/1] KVM: x86: Propagate AMD-specific IBRS bits to guests 2023-03-01 18:58 [PATCH v2 0/1] KVM: x86: Propagate AMD-specific IBRS bits to guests Takahiro Itazuri @ 2023-03-01 18:58 ` Takahiro Itazuri 2023-03-24 21:15 ` Sean Christopherson 0 siblings, 1 reply; 4+ messages in thread From: Takahiro Itazuri @ 2023-03-01 18:58 UTC (permalink / raw) To: kvm, Sean Christopherson, Paolo Bonzini Cc: linux-kernel, Takahiro Itazuri, Takahiro Itazuri VMMs retrieve supported CPUID features via KVM_GET_SUPPORTED_CPUID to construct CPUID information to be passed to KVM_SET_CPUID2. Most CPUID feature bits related to speculative attacks are propagated from host CPUID. AMD processors have AMD-specific IBRS related bits in CPUID Fn8000_0008_EBX (ref: AMD64 Architecture Programmer's Manual Volume 3: General-Purpose and System Instructions) and some bits are not propagated to guests. Enable propagation of these bits to guests, so that guests can see the same security information as the host without VMM action. Signed-off-by: Takahiro Itazuri <itazur@amazon.com> --- arch/x86/kvm/cpuid.c | 5 +++-- arch/x86/kvm/reverse_cpuid.h | 5 +++++ 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 596061c1610e..c297064208dd 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -704,8 +704,9 @@ void kvm_set_cpu_caps(void) kvm_cpu_cap_mask(CPUID_8000_0008_EBX, F(CLZERO) | F(XSAVEERPTR) | F(WBNOINVD) | F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) | - F(AMD_SSB_NO) | F(AMD_STIBP) | F(AMD_STIBP_ALWAYS_ON) | - __feature_bit(KVM_X86_FEATURE_AMD_PSFD) + F(AMD_SSB_NO) | F(AMD_STIBP) | F(AMD_IBRS_ALWAYS_ON) | + F(AMD_STIBP_ALWAYS_ON) | F(AMD_IBRS_PREFERRED) | + F(AMD_IBRS_SAME_MODE) | __feature_bit(KVM_X86_FEATURE_AMD_PSFD) ); /* diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h index 042d0aca3c92..1e538e29b117 100644 --- a/arch/x86/kvm/reverse_cpuid.h +++ b/arch/x86/kvm/reverse_cpuid.h @@ -43,6 +43,11 @@ enum kvm_only_cpuid_leafs { #define X86_FEATURE_AVX_NE_CONVERT KVM_X86_FEATURE(CPUID_7_1_EDX, 5) #define X86_FEATURE_PREFETCHITI KVM_X86_FEATURE(CPUID_7_1_EDX, 14) +/* AMD-specific IBRS hint bits, CPUID level 0x80000008 (EBX) */ +#define X86_FEATURE_AMD_IBRS_ALWAYS_ON KVM_X86_FEATURE(CPUID_8000_0008_EBX, 16) +#define X86_FEATURE_AMD_IBRS_PREFERRED KVM_X86_FEATURE(CPUID_8000_0008_EBX, 18) +#define X86_FEATURE_AMD_IBRS_SAME_MODE KVM_X86_FEATURE(CPUID_8000_0008_EBX, 19) + struct cpuid_reg { u32 function; u32 index; -- 2.38.0 ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2 1/1] KVM: x86: Propagate AMD-specific IBRS bits to guests 2023-03-01 18:58 ` [PATCH v2 1/1] " Takahiro Itazuri @ 2023-03-24 21:15 ` Sean Christopherson 2023-03-24 23:40 ` Jim Mattson 0 siblings, 1 reply; 4+ messages in thread From: Sean Christopherson @ 2023-03-24 21:15 UTC (permalink / raw) To: Takahiro Itazuri; +Cc: kvm, Paolo Bonzini, linux-kernel, Takahiro Itazuri On Wed, Mar 01, 2023, Takahiro Itazuri wrote: > VMMs retrieve supported CPUID features via KVM_GET_SUPPORTED_CPUID to > construct CPUID information to be passed to KVM_SET_CPUID2. Most CPUID > feature bits related to speculative attacks are propagated from host > CPUID. AMD processors have AMD-specific IBRS related bits in CPUID > Fn8000_0008_EBX (ref: AMD64 Architecture Programmer's Manual Volume 3: > General-Purpose and System Instructions) and some bits are not > propagated to guests. > > Enable propagation of these bits to guests, so that guests can see the > same security information as the host without VMM action. Please provide some description on what these bits do, and more importantly why no action is required to virtualize them in KVM, even if it seems obvious. We've had a few goofs with respect to mitigations across guest domains, I just want to be extra paranoid that we document upfront why it's ok (recommended?) to advertise this information to the guest. > Signed-off-by: Takahiro Itazuri <itazur@amazon.com> > --- > arch/x86/kvm/cpuid.c | 5 +++-- > arch/x86/kvm/reverse_cpuid.h | 5 +++++ > 2 files changed, 8 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index 596061c1610e..c297064208dd 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -704,8 +704,9 @@ void kvm_set_cpu_caps(void) > kvm_cpu_cap_mask(CPUID_8000_0008_EBX, > F(CLZERO) | F(XSAVEERPTR) | > F(WBNOINVD) | F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) | > - F(AMD_SSB_NO) | F(AMD_STIBP) | F(AMD_STIBP_ALWAYS_ON) | > - __feature_bit(KVM_X86_FEATURE_AMD_PSFD) > + F(AMD_SSB_NO) | F(AMD_STIBP) | F(AMD_IBRS_ALWAYS_ON) | > + F(AMD_STIBP_ALWAYS_ON) | F(AMD_IBRS_PREFERRED) | > + F(AMD_IBRS_SAME_MODE) | __feature_bit(KVM_X86_FEATURE_AMD_PSFD) > ); > > /* > diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h > index 042d0aca3c92..1e538e29b117 100644 > --- a/arch/x86/kvm/reverse_cpuid.h > +++ b/arch/x86/kvm/reverse_cpuid.h > @@ -43,6 +43,11 @@ enum kvm_only_cpuid_leafs { > #define X86_FEATURE_AVX_NE_CONVERT KVM_X86_FEATURE(CPUID_7_1_EDX, 5) > #define X86_FEATURE_PREFETCHITI KVM_X86_FEATURE(CPUID_7_1_EDX, 14) > > +/* AMD-specific IBRS hint bits, CPUID level 0x80000008 (EBX) */ > +#define X86_FEATURE_AMD_IBRS_ALWAYS_ON KVM_X86_FEATURE(CPUID_8000_0008_EBX, 16) > +#define X86_FEATURE_AMD_IBRS_PREFERRED KVM_X86_FEATURE(CPUID_8000_0008_EBX, 18) > +#define X86_FEATURE_AMD_IBRS_SAME_MODE KVM_X86_FEATURE(CPUID_8000_0008_EBX, 19) These belong in cpufeatures.h, see the rest of the discussion in v1[*]. Sorry for the runaround :-( [*] https://lore.kernel.org/all/e5bf7da5-df29-31c6-6d33-81bbecb849ba@redhat.com ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2 1/1] KVM: x86: Propagate AMD-specific IBRS bits to guests 2023-03-24 21:15 ` Sean Christopherson @ 2023-03-24 23:40 ` Jim Mattson 0 siblings, 0 replies; 4+ messages in thread From: Jim Mattson @ 2023-03-24 23:40 UTC (permalink / raw) To: Sean Christopherson Cc: Takahiro Itazuri, kvm, Paolo Bonzini, linux-kernel, Takahiro Itazuri On Fri, Mar 24, 2023 at 2:16 PM Sean Christopherson <seanjc@google.com> wrote: > > On Wed, Mar 01, 2023, Takahiro Itazuri wrote: > > VMMs retrieve supported CPUID features via KVM_GET_SUPPORTED_CPUID to > > construct CPUID information to be passed to KVM_SET_CPUID2. Most CPUID > > feature bits related to speculative attacks are propagated from host > > CPUID. AMD processors have AMD-specific IBRS related bits in CPUID > > Fn8000_0008_EBX (ref: AMD64 Architecture Programmer's Manual Volume 3: > > General-Purpose and System Instructions) and some bits are not > > propagated to guests. > > > > Enable propagation of these bits to guests, so that guests can see the > > same security information as the host without VMM action. Usually, I can count on Sean for the semantic nitpick: This propagates bits only to the userspace VMM. They may make it to the guest. They may not. ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-03-24 23:40 UTC | newest] Thread overview: 4+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2023-03-01 18:58 [PATCH v2 0/1] KVM: x86: Propagate AMD-specific IBRS bits to guests Takahiro Itazuri 2023-03-01 18:58 ` [PATCH v2 1/1] " Takahiro Itazuri 2023-03-24 21:15 ` Sean Christopherson 2023-03-24 23:40 ` Jim Mattson
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