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SubjectRe: [PATCH] KVM: x86: remove bogus user-triggerable WARN_ON
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Paolo Bonzini <pbonzini@redhat.com> writes:
> On 20/03/20 16:23, Thomas Gleixner wrote:
>> Thomas Gleixner <tglx@linutronix.de> writes:
>>
>>> Paolo Bonzini <pbonzini@redhat.com> writes:
>>>> The WARN_ON is essentially comparing a user-provided value with 0. It is
>>>> trivial to trigger it just by passing garbage to KVM_SET_CLOCK. Guests
>>>> can break if you do so, but if it hurts when you do like this just do not
>>>> do it.
>>>
>>> Yes, it's a user provided value and it's completely unchecked. If that
>>> value is bogus then the guest will go sideways because timekeeping is
>>> completely busted. At least you should explain WHY you don't care.
>>
>> Or why it does not matter....
>
> I can change the commit message to "Guests can break if you do so, but
> the same applies to every KVM_SET_* ioctl". It's impossible to be sure
> that userspace doesn't ever send a bogus KVM_SET_CLOCK and later
> rectifies it with the right value.

Yes please.

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