linux-kernel - Re: [PATCH 1/8] KVM: SEV-ES: fix length of string I/O

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Message-ID: <707a0a5d-413e-b80d-89be-17bfca8fc44c@redhat.com>
Date:   Mon, 25 Oct 2021 10:59:04 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Marc Orr <marcorr@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        fwilhelm@...gle.com, seanjc@...gle.com, oupton@...gle.com,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/8] KVM: SEV-ES: fix length of string I/O

On 25/10/21 03:31, Marc Orr wrote:
> I could be missing something, but I'm pretty sure that this is wrong.
> The GHCB spec says that `exit_info_2` is the `rep` count. Not the
> string length.
> 
> For example, given a `rep outsw` instruction, with `ECX` set to `8`,
> the rep count written into `SW_EXITINFO2` should be eight x86 words
> (i.e., 16 bytes) and the IO size should be one x86 word (i.e., 2
> bytes). In other words, the code was correct before this patch. This
> patch is incorrectly dividing the rep count by the IO size, causing
> the string IO to be truncated.

Then what's wrong is _also_ the call to setup_vmgexit_scratch, because 
that one definitely expects bytes:

                 scratch_va = kzalloc(len, GFP_KERNEL_ACCOUNT);

Paolo