linux-kernel - [PATCH 2/2] KVM: x86: Use memcmp in kvm_cpuid_check

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Date:   Mon, 24 Jan 2022 11:36:06 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] KVM: x86: Use memcmp in kvm_cpuid_check_equal()

kvm_cpuid_check_equal() should also check .flags equality but instead
of adding it to the existing check, just switch to using memcmp() for
the whole 'struct kvm_cpuid_entry2'.

When .flags are not checked, kvm_cpuid_check_equal() may allow an update
which it shouldn't but kvm_set_cpuid() does not actually update anything
and just returns success.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/cpuid.c | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 89d7822a8f5b..7dd9c8f4f46e 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -123,20 +123,11 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu,
 static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
 				 int nent)
 {
-	struct kvm_cpuid_entry2 *orig;
-	int i;
-
 	if (nent != vcpu->arch.cpuid_nent)
 		return -EINVAL;
 
-	for (i = 0; i < nent; i++) {
-		orig = &vcpu->arch.cpuid_entries[i];
-		if (e2[i].function != orig->function ||
-		    e2[i].index != orig->index ||
-		    e2[i].eax != orig->eax || e2[i].ebx != orig->ebx ||
-		    e2[i].ecx != orig->ecx || e2[i].edx != orig->edx)
-			return -EINVAL;
-	}
+	if (memcmp(e2, vcpu->arch.cpuid_entries, nent * sizeof(*e2)))
+		return -EINVAL;
 
 	return 0;
 }
-- 
2.34.1