linux-kernel - Re: [RFC PATCH v4 0/2] Deprecate BUG() in pte_list

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Date:   Tue, 6 Dec 2022 15:06:36 -0800
From:   Mingwei Zhang <mizhang@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Nagareddy Reddy <nspreddy@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        David Matlack <dmatlack@...gle.com>
Subject: Re: [RFC PATCH v4 0/2] Deprecate BUG() in pte_list_remove() in shadow mmu

gentle ping on this one?

On Tue, Nov 29, 2022 at 11:12 AM Mingwei Zhang <mizhang@...gle.com> wrote:
>
> Deprecate BUG() in pte_list_remove() in shadow mmu to avoid crashing a
> physical machine. There are several reasons and motivations to do so:
>
> MMU bug is difficult to discover due to various racing conditions and
> corner cases and thus it extremely hard to debug. The situation gets much
> worse when it triggers the shutdown of a host. Host machine crash might
> eliminates everything including the potential clues for debugging.
>
> From cloud computing service perspective, BUG() or BUG_ON() is probably no
> longer appropriate as the host reliability is top priority. Crashing the
> physical machine is almost never a good option as it eliminates innocent
> VMs and cause service outage in a larger scope. Even worse, if attacker can
> reliably triggers this code by diverting the control flow or corrupting the
> memory, then this becomes vm-of-death attack. This is a huge attack vector
> to cloud providers, as the death of one single host machine is not the end
> of the story. Without manual interferences, a failed cloud job may be
> dispatched to other hosts and continue host crashes until all of them are
> dead.
>
> For the above reason, we propose the replacement of BUG() in
> pte_list_remove() with KVM_BUG() to crash just the VM itself.
>
> v3 - v4:
>  - update code to integrate messages into KVM_BUG() [seanjc].
>  - update commit message [seanjc].
>
> v2 -> v3:
>  - plumb @kvm all the way to pte_list_remove() [seanjc, pbonzini]
>  - https://lore.kernel.org/lkml/20221128002043.1555543-1-mizhang@google.com/
>
> v1 -> v2:
>  - compile test the code.
>  - fill KVM_BUG() with kvm_get_running_vcpu()->kvm
>  - https://lore.kernel.org/all/20221124003505.424617-1-mizhang@google.com/
>
> rfc v1:
>  - https://lore.kernel.org/all/20221123231206.274392-1-mizhang@google.com/
>
>
> Mingwei Zhang (2):
>   KVM: x86/mmu: plumb struct kvm all the way to pte_list_remove()
>   KVM: x86/mmu: replace BUG() with KVM_BUG() in shadow mmu
>
>  arch/x86/kvm/mmu/mmu.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
>
> --
> 2.38.1.584.g0f3c55d4c2-goog
>