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Re: [PATCH v2 4/6] target/i386/sev: Fail when invalid hashes table area

From: Daniel P . Berrangé
Subject: Re: [PATCH v2 4/6] target/i386/sev: Fail when invalid hashes table area detected
Date: Thu, 11 Nov 2021 09:29:44 +0000
User-agent: Mutt/2.0.7 (2021-05-04)

On Mon, Nov 08, 2021 at 01:48:38PM +0000, Dov Murik wrote:
> Commit cff03145ed3c ("sev/i386: Introduce sev_add_kernel_loader_hashes
> for measured linux boot", 2021-09-30) introduced measured direct boot
> with -kernel, using an OVMF-designated hashes table which QEMU fills.
> However, no checks are performed on the validity of the hashes area
> designated by OVMF.  Specifically, if OVMF publishes the
> SEV_HASH_TABLE_RV_GUID entry but it is filled with zeroes, this will
> cause QEMU to write the hashes entries over the first page of the
> guest's memory (GPA 0).
> Add validity checks to the published area.  If the hashes table area's
> base address is zero, or its size is too small to fit the aligned hashes
> table, display an error and stop the guest launch.  In such case, the
> following error will be displayed:
>     qemu-system-x86_64: SEV: guest firmware hashes table area is invalid 
> (base=0x0 size=0x0)
> Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
> Reported-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
>  target/i386/sev.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

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