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From:   Peter Gonda <pgonda@google.com>
Date:   Wed, 16 Nov 2022 10:57:09 -0700
Message-ID: <CAMkAt6r8ocB2b0gympDCX3zQCOOow=N+fGtD0s5jyP3ayt2-Ug@mail.gmail.com>
Subject: Re: [PATCH V4] virt: sev: Prevent IV reuse in SNP guest driver
To:     Borislav Petkov <bp@suse.de>
Cc:     Tom Lendacky <thomas.lendacky@amd.com>,
        Dionna Glaze <dionnaglaze@google.com>,
        Michael Roth <michael.roth@amd.com>,
        Haowen Bai <baihaowen@meizu.com>,
        Yang Yingliang <yangyingliang@huawei.com>,
        Marc Orr <marcorr@google.com>,
        David Rientjes <rientjes@google.com>,
        Ashish Kalra <Ashish.Kalra@amd.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
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On Wed, Nov 16, 2022 at 10:28 AM Borislav Petkov <bp@suse.de> wrote:
>
> On Wed, Nov 16, 2022 at 10:10:58AM -0700, Peter Gonda wrote:
> > I think another comment above the first snp_issue_guest_request()
> > could help too. Saying once we call this function we either need to
> > increment the sequence number or wipe the VMPCK to ensure the
> > encryption scheme is safe.
>
> And make that explicit pls:
>
>         /*
>          * If the extended guest request fails due to having to small of a
>          * certificate data buffer retry the same guest request without the
>          * extended data request...
>
>          ... in order to not have to reuse the IV.
>
>
> I have to admit, the flow in that function is still not optimal but I
> haven't stared at it long enough to have a better idea...

Thanks for all the feedback Tom and Boris. I've sent out a V5. I hope
I've gotten the grammar correct in these comments.