Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:
> On 1/24/22 11:36, Vitaly Kuznetsov wrote:
>> 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@xxxxxxxxxx>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
>> ---
>> 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;
>
> Hmm, not sure about that due to the padding in struct kvm_cpuid_entry2.
> It might break userspace that isn't too careful about zeroing it.
FWIW, QEMU zeroes the whole thing before setting individual CPUID
entries. Legacy KVM_SET_CPUID call is also not afffected as it copies
entries to a newly allocated "struct kvm_cpuid_entry2[]" and explicitly
zeroes padding.
Do we need to at least add a check for ".flags"?
>
> Queued patch 1 though.
>
> Paolo
>
--
Vitaly
