kvm: x86: Exclude unpermitted xfeatures at KVM_GET_SUPPORTED_CPUID
KVM_GET_SUPPORTED_CPUID should not include any dynamic xstates in
CPUID[0xD] if they have not been requested with prctl. Otherwise
a process which directly passes KVM_GET_SUPPORTED_CPUID to
KVM_SET_CPUID2 would now fail even if it doesn't intend to use a
dynamically enabled feature. Userspace must know that prctl is
required and allocate >4K xstate buffer before setting any dynamic
bit.
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20220105123532.12586-5-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index f3e6fda..eb52dde 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -815,11 +815,13 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
goto out;
}
break;
- case 0xd:
- entry->eax &= supported_xcr0;
+ case 0xd: {
+ u64 guest_perm = xstate_get_guest_group_perm();
+
+ entry->eax &= supported_xcr0 & guest_perm;
entry->ebx = xstate_required_size(supported_xcr0, false);
entry->ecx = entry->ebx;
- entry->edx &= supported_xcr0 >> 32;
+ entry->edx &= (supported_xcr0 & guest_perm) >> 32;
if (!supported_xcr0)
break;
@@ -866,6 +868,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
entry->edx = 0;
}
break;
+ }
case 0x12:
/* Intel SGX */
if (!kvm_cpu_cap_has(X86_FEATURE_SGX)) {