[PATCH v2 05/14] KVM: x86: Override reported SME/SEV feature flags with host mask

Sean Christopherson
2021-01-14T01:48:50Z

Add a reverse-CPUID entry for the memory encryption word, 0x8000001F.EAX,
and use it to override the supported CPUID flags reported to userspace.
Masking the reported CPUID flags avoids over-reporting KVM support, e.g.
without the mask a SEV-SNP capable CPU may incorrectly advertise SNP
support to userspace.

Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/cpuid.c | 2 ++
arch/x86/kvm/cpuid.h | 1 +
2 files changed, 3 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 13036cf0b912..b7618cdd06b5 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -855,6 +855,8 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
case 0x8000001F:
if (!boot_cpu_has(X86_FEATURE_SEV))
entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+ else
+ cpuid_entry_override(entry, CPUID_8000_001F_EAX);
break;
/*Add support for Centaur's CPUID instruction*/
case 0xC0000000:
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index dc921d76e42e..8b6fc9bde248 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -63,6 +63,7 @@ static const struct cpuid_reg reverse_cpuid[] = {
[CPUID_8000_0007_EBX] = {0x80000007, 0, CPUID_EBX},
[CPUID_7_EDX] = { 7, 0, CPUID_EDX},
[CPUID_7_1_EAX] = { 7, 1, CPUID_EAX},
+ [CPUID_8000_001F_EAX] = {0x8000001f, 1, CPUID_EAX},
};

/*
--
2.30.0.284.gd98b1dd5eaa7-goog