On Mon, Jan 24, 2022, Vitaly Kuznetsov wrote:
> Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:
> >> + 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.
Given that we already are fully committed to potentially breaking userspace by
disallowing KVM_SET_CPUID{2} after KVM_RUN, we might as well get greedy.
> 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"?
Yes.
