linux-kernel - Re: [PATCH] KVM: x86: remove bogus user-triggerable WARN

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Message-ID: <87o8sr59v9.fsf@nanos.tec.linutronix.de>
Date:   Fri, 20 Mar 2020 16:22:50 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     syzbot+00be5da1d75f1cc95f6b@...kaller.appspotmail.com,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH] KVM: x86: remove bogus user-triggerable WARN_ON

Paolo Bonzini <pbonzini@...hat.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.

Thanks,

        tglx