linux-kernel - Re: [PATCH V4] virt: sev: Prevent IV reuse in SNP guest driver

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Date:   Wed, 16 Nov 2022 18:28:38 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Peter Gonda <pgonda@...gle.com>
Cc:     Tom Lendacky <thomas.lendacky@....com>,
        Dionna Glaze <dionnaglaze@...gle.com>,
        Michael Roth <michael.roth@....com>,
        Haowen Bai <baihaowen@...zu.com>,
        Yang Yingliang <yangyingliang@...wei.com>,
        Marc Orr <marcorr@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Ashish Kalra <Ashish.Kalra@....com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH V4] virt: sev: Prevent IV reuse in SNP guest driver

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...

Thx.

-- 
Regards/Gruss,
    Boris.

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