linux-kernel - Re: [PATCH] KVM: SVM: Use kzalloc for sev ioctl interfaces to prevent kernel memory leak.

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Date:   Fri, 13 May 2022 09:37:15 -0400
From:   Peter Gonda <pgonda@...gle.com>
To:     Ashish Kalra <Ashish.Kalra@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        Borislav Petkov <bp@...en8.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Nguyen <theflow@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        John Allen <john.allen@....com>
Subject: Re: [PATCH] KVM: SVM: Use kzalloc for sev ioctl interfaces to prevent
 kernel memory leak.

On Thu, May 12, 2022 at 4:23 PM Ashish Kalra <Ashish.Kalra@....com> wrote:
>
> From: Ashish Kalra <ashish.kalra@....com>
>
> For some sev ioctl interfaces, the length parameter that is passed maybe
> less than or equal to SEV_FW_BLOB_MAX_SIZE, but larger than the data
> that PSP firmware returns. In this case, kmalloc will allocate memory
> that is the size of the input rather than the size of the data.
> Since PSP firmware doesn't fully overwrite the allocated buffer, these
> sev ioctl interface may return uninitialized kernel slab memory.
>
> Reported-by: Andy Nguyen <theflow@...gle.com>
> Suggested-by: David Rientjes <rientjes@...gle.com>
> Suggested-by: Peter Gonda <pgonda@...gle.com>
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> ---
>  arch/x86/kvm/svm/sev.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>

Can we just update all the kmalloc()s that buffers get given to the
PSP? For instance doesn't sev_send_update_data() have an issue?
Reading the PSP spec it seems like a user can call this ioctl with a
large hdr_len and the PSP will only fill out what's actually required
like in these fixed up cases? This is assuming the PSP is written to
spec (and just the current version). I'd rather have all of these
instances updated.