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KVM: x86: Reject userspace attempts to access ARCH_CAPABILITIES w/o support

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Reject userspace accesses to ARCH_CAPABILITIES if the MSR isn't supposed
to exist, according to guest CPUID.  However, "reject" accesses with
KVM_MSR_RET_UNSUPPORTED, so that reads get '0' and writes of '0' are
ignored if KVM advertised support ARCH_CAPABILITIES.

KVM's ABI is that userspace must set guest CPUID prior to setting MSRs,
and that setting MSRs that aren't supposed exist is disallowed (modulo the
'0' exemption).

Link: https://lore.kernel.org/r/20240802185511.305849-7-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-08-02 11:55:08 -07:00
parent a103911119
commit a5d563890b
1 changed files with 5 additions and 5 deletions
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10
arch/x86/kvm/x86.c
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@ -3795,8 +3795,9 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
vcpu->arch.microcode_version = data;
break;
case MSR_IA32_ARCH_CAPABILITIES:
if (!msr_info->host_initiated)
return 1;
if (!msr_info->host_initiated ||
!guest_cpuid_has(vcpu, X86_FEATURE_ARCH_CAPABILITIES))
return KVM_MSR_RET_UNSUPPORTED;
vcpu->arch.arch_capabilities = data;
break;
case MSR_IA32_PERF_CAPABILITIES:
@ -4256,9 +4257,8 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
msr_info->data = vcpu->arch.microcode_version;
break;
case MSR_IA32_ARCH_CAPABILITIES:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_ARCH_CAPABILITIES))
return 1;
if (!guest_cpuid_has(vcpu, X86_FEATURE_ARCH_CAPABILITIES))
return KVM_MSR_RET_UNSUPPORTED;
msr_info->data = vcpu->arch.arch_capabilities;
break;
case MSR_IA32_PERF_CAPABILITIES: