linux-kernel - Re: [PATCH v2 7/8] KVM: x86: Bug the VM if the emulator generates a bogus exception vector

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Date:   Tue, 31 May 2022 11:06:12 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Robert Dinse <nanook@...imo.com>
Subject: Re: [PATCH v2 7/8] KVM: x86: Bug the VM if the emulator generates a
 bogus exception vector

On Thu, May 26, 2022 at 09:08:16PM +0000, Sean Christopherson wrote:
> Bug the VM if KVM's emulator attempts to inject a bogus exception vector.
> The guest is likely doomed even if KVM continues on, and propagating a
> bad vector to the rest of KVM runs the risk of breaking other assumptions
> in KVM and thus triggering a more egregious bug.
> 
> All existing users of emulate_exception() have hardcoded vector numbers
> (__load_segment_descriptor() uses a few different vectors, but they're
> all hardcoded), and future users are likely to follow suit, i.e. the
> change to emulate_exception() is a glorified nop.
> 
> As for the ctxt->exception.vector check in x86_emulate_insn(), the few
> known times the WARN has been triggered in the past is when the field was
> not set when synthesizing a fault, i.e. for all intents and purposes the
> check protects against consumption of uninitialized data.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook