linux-kernel - Re: [PATCH v3 7/9] KVM: VMX: Add guest physical address check in EPT violation and misconfig

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Date:   Fri, 15 Jan 2021 11:35:42 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Mohammed Gamal <mgamal@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Aaron Lewis <aaronlewis@...gle.com>
Subject: Re: [PATCH v3 7/9] KVM: VMX: Add guest physical address check in EPT
 violation and misconfig

On Fri, Oct 23, 2020 at 10:43 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 23/10/20 19:23, Jim Mattson wrote:
> >> The information that we need is _not_ that provided by the advanced
> >> VM-exit information (or by a page walk).  If a page is neither writable
> >> nor executable, the advanced information doesn't say if the injected #PF
> >> should be a W=1 or a F=1 fault.  We need the information in bits 0..2 of
> >> the exit qualification for the final access, which however is not
> >> available for the paging-structure access.
> >>
> > Are you planning to extend the emulator, then, to support all
> > instructions? I'm not sure where you are going with this.
>
> I'm going to fix the bit 8=1 case, but for bit 8=0 there's not much that
> you can do.  In all likelihood the guest is buggy anyway.

Did this drop off your radar? Are you still planning to fix the bit8=1
case to use advanced EPT exit qualification information? Or did I just
miss it?

> It would be possible to only do the decode part of the emulator to get
> the PFEC (matching the GVA from the vmexit to the memory operand, for
> example, and retrying if the instruction is unexpected).  Then one would
> only need enough VEX/EVEX parsing to process the decoding.
>
> Paolo
>