linux-kernel - Re: [PATCH 3/3] KVM: SEV: remove ghcb variable declarations

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Message-ID: <762e3471-834c-ad7f-337e-292394e6dc19@amd.com>
Date:   Tue, 15 Aug 2023 10:52:28 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     pgonda@...gle.com, seanjc@...gle.com, theflow@...gle.com,
        vkuznets@...hat.com
Subject: Re: [PATCH 3/3] KVM: SEV: remove ghcb variable declarations

On 8/4/23 12:33, Paolo Bonzini wrote:
> To avoid possible time-of-check/time-of-use issues, the GHCB should
> almost never be accessed outside dump_ghcb, sev_es_sync_to_ghcb
> and sev_es_sync_from_ghcb.  The only legitimate uses are to set the
> exitinfo fields and to find the address of the scratch area embedded
> in the ghcb.  Accessing ghcb_usage also goes through svm->sev_es.ghcb
> in sev_es_validate_vmgexit(), but that is because anyway the value is
> not used.
> 
> Removing a shortcut variable that contains the value of svm->sev_es.ghcb
> makes these cases a bit more verbose, but it limits the chance of someone
> reading the ghcb by mistake.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> ---
>   arch/x86/kvm/svm/sev.c | 30 ++++++++++++------------------
>   1 file changed, 12 insertions(+), 18 deletions(-)
>