Messages in this thread | | | Subject | Re: [PATCH] KVM: x86: avoid incorrect writes to host MSR_IA32_SPEC_CTRL | From | Xiaoyao Li <> | Date | Fri, 24 Jan 2020 16:00:15 +0800 |
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On 1/21/2020 9:48 PM, Paolo Bonzini wrote: > If the guest is configured to have SPEC_CTRL but the host does not > (which is a nonsensical configuration but these are not explicitly > forbidden) then a host-initiated MSR write can write vmx->spec_ctrl > (respectively svm->spec_ctrl) and trigger a #GP when KVM tries to > restore the host value of the MSR. Add a more comprehensive check > for valid bits of SPEC_CTRL, covering host CPUID flags and, > since we are at it and it is more correct that way, guest CPUID > flags too. > > For AMD, remove the unnecessary is_guest_mode check around setting > the MSR interception bitmap, so that the code looks the same as > for Intel. > > Cc: Jim Mattson <jmattson@redhat.com> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > arch/x86/kvm/svm.c | 9 +++------ > arch/x86/kvm/vmx/vmx.c | 7 +++---- > arch/x86/kvm/x86.c | 22 ++++++++++++++++++++++ > arch/x86/kvm/x86.h | 1 + > 4 files changed, 29 insertions(+), 10 deletions(-) > > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > index b7c5369c7998..235a7e51de96 100644 > --- a/arch/x86/kvm/svm.c > +++ b/arch/x86/kvm/svm.c > @@ -4324,12 +4324,10 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) > !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD)) > return 1; > > - /* The STIBP bit doesn't fault even if it's not advertised */ > - if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD)) > + if (data & ~kvm_spec_ctrl_valid_bits(vcpu)) > return 1; > > svm->spec_ctrl = data; > - > if (!data) > break; > > @@ -4353,13 +4351,12 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) > > if (data & ~PRED_CMD_IBPB) > return 1; > - > + if (!boot_cpu_has(X86_FEATURE_AMD_IBPB)) > + return 1; > if (!data) > break; > > wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB); > - if (is_guest_mode(vcpu)) > - break; > set_msr_interception(svm->msrpm, MSR_IA32_PRED_CMD, 0, 1); > break; > case MSR_AMD64_VIRT_SPEC_CTRL: > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index bdbf27e92851..112d2314231d 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -1998,12 +1998,10 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)) > return 1; > > - /* The STIBP bit doesn't fault even if it's not advertised */ > - if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD)) > + if (data & ~kvm_spec_ctrl_valid_bits(vcpu)) > return 1; > > vmx->spec_ctrl = data; > - > if (!data) > break; > > @@ -2037,7 +2035,8 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > > if (data & ~PRED_CMD_IBPB) > return 1; > - > + if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL)) > + return 1; > if (!data) > break; > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 9f24f5d16854..141fb129c6bf 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -10389,6 +10389,28 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu) > } > EXPORT_SYMBOL_GPL(kvm_arch_no_poll); > > +bool kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu)
The return type should be u64.
> +{ > + uint64_t bits = SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD; > + > + /* The STIBP bit doesn't fault even if it's not advertised */ > + if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) && > + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS)) > + bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP); > + if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL) && > + !boot_cpu_has(X86_FEATURE_AMD_IBRS)) > + bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP); > + > + if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL_SSBD) && > + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD)) > + bits &= ~SPEC_CTRL_SSBD; > + if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) && > + !boot_cpu_has(X86_FEATURE_AMD_SSBD)) > + bits &= ~SPEC_CTRL_SSBD; > + > + return bits; > +} > +EXPORT_SYMBOL_GPL(kvm_spec_ctrl_valid_bits); > > EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit); > EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio); > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h > index ab715cee3653..bc38ac695776 100644 > --- a/arch/x86/kvm/x86.h > +++ b/arch/x86/kvm/x86.h > @@ -367,5 +367,6 @@ static inline bool kvm_pat_valid(u64 data) > > void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu); > void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu); > +bool kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu); > > #endif >
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