From: Sean Christopherson <seanjc@google.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
Igor Mammedov <imammedo@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] KVM: x86: Use memcmp in kvm_cpuid_check_equal()
Date: Mon, 24 Jan 2022 16:52:16 +0000 [thread overview]
Message-ID: <Ye7ZQJ6NYoZqK9yk@google.com> (raw)
In-Reply-To: <87bl01i2zl.fsf@redhat.com>
On Mon, Jan 24, 2022, Vitaly Kuznetsov wrote:
> Paolo Bonzini <pbonzini@redhat.com> 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.
next prev parent reply other threads:[~2022-01-24 16:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-24 10:36 [PATCH 0/2] KVM: x86: Partially allow KVM_SET_CPUID{,2} follow-up Vitaly Kuznetsov
2022-01-24 10:36 ` [PATCH 1/2] KVM: x86: Move CPUID.(EAX=0x12,ECX=1) mangling to __kvm_update_cpuid_runtime() Vitaly Kuznetsov
2022-01-24 10:36 ` [PATCH 2/2] KVM: x86: Use memcmp in kvm_cpuid_check_equal() Vitaly Kuznetsov
2022-01-24 14:02 ` Paolo Bonzini
2022-01-24 15:10 ` Vitaly Kuznetsov
2022-01-24 16:52 ` Sean Christopherson [this message]
2022-01-24 17:07 ` Paolo Bonzini
2022-01-24 19:08 ` Sean Christopherson
2022-01-24 21:03 ` Joe Perches
2022-01-26 10:03 ` Vitaly Kuznetsov
2022-01-26 16:02 ` Sean Christopherson
2022-01-26 16:25 ` Vitaly Kuznetsov
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