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KVM: x86: Check XSS validity against guest CPUIDs 

Maintain per-guest valid XSS bits and check XSS validity against them
rather than against KVM capabilities. This is to prevent bits that are
supported by KVM but not supported for a guest from being set.

Opportunistically return KVM_MSR_RET_UNSUPPORTED on IA32_XSS MSR accesses
if guest CPUID doesn't enumerate X86_FEATURE_XSAVES. Since
KVM_MSR_RET_UNSUPPORTED takes care of host_initiated cases, drop the
host_initiated check.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Link: https://lore.kernel.org/r/20250919223258.1604852-7-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Chao Gao 2025-09-19 15:32:13 -07:00 committed by Sean Christopherson
parent c0a5f29891
commit 338543cbe0
3 changed files with 17 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/x86/include/asm/kvm_host.h
View File

@ -815,7 +815,6 @@ struct kvm_vcpu_arch {
bool at_instruction_boundary;
bool tpr_access_reporting;
bool xfd_no_write_intercept;
u64 ia32_xss;
u64 microcode_version;
u64 arch_capabilities;
u64 perf_capabilities;
@ -876,6 +875,8 @@ struct kvm_vcpu_arch {
u64 xcr0;
u64 guest_supported_xcr0;
u64 ia32_xss;
u64 guest_supported_xss;
struct kvm_pio_request pio;
void *pio_data;

12
arch/x86/kvm/cpuid.c
View File

@ -263,6 +263,17 @@ static u64 cpuid_get_supported_xcr0(struct kvm_vcpu *vcpu)
return (best->eax | ((u64)best->edx << 32)) & kvm_caps.supported_xcr0;
}
static u64 cpuid_get_supported_xss(struct kvm_vcpu *vcpu)
{
struct kvm_cpuid_entry2 *best;
best = kvm_find_cpuid_entry_index(vcpu, 0xd, 1);
if (!best)
return 0;
return (best->ecx | ((u64)best->edx << 32)) & kvm_caps.supported_xss;
}
static __always_inline void kvm_update_feature_runtime(struct kvm_vcpu *vcpu,
struct kvm_cpuid_entry2 *entry,
unsigned int x86_feature,
@ -424,6 +435,7 @@ void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
}
vcpu->arch.guest_supported_xcr0 = cpuid_get_supported_xcr0(vcpu);
vcpu->arch.guest_supported_xss = cpuid_get_supported_xss(vcpu);
vcpu->arch.pv_cpuid.features = kvm_apply_cpuid_pv_features_quirk(vcpu);

7
arch/x86/kvm/x86.c
View File

@ -3984,15 +3984,14 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
}
break;
case MSR_IA32_XSS:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
return 1;
if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
return KVM_MSR_RET_UNSUPPORTED;
/*
* KVM supports exposing PT to the guest, but does not support
* IA32_XSS[bit 8]. Guests have to use RDMSR/WRMSR rather than
* XSAVES/XRSTORS to save/restore PT MSRs.
*/
if (data & ~kvm_caps.supported_xss)
if (data & ~vcpu->arch.guest_supported_xss)
return 1;
vcpu->arch.ia32_xss = data;
vcpu->arch.cpuid_dynamic_bits_dirty = true;