On 11/3/22 10:23, Peter Gonda wrote:
The ASP and an SNP guest use a series of AES-GCM keys called VMPCKs to
communicate securely with each other. The IV to this scheme is a
sequence number that both the ASP and the guest track. Currently this
sequence number in a guest request must exactly match the sequence
number tracked by the ASP. This means that if the guest sees an error
from the host during a request it can only retry that exact request or
disable the VMPCK to prevent an IV reuse. AES-GCM cannot tolerate IV
reuse see:
https://csrc.nist.gov/csrc/media/projects/block-cipher-techniques/documents/bcm/comments/800-38-series-drafts/gcm/joux_comments.pdf
To handle userspace querying the cert_data length handle_guest_request()
now: saves the number of pages required by the host, retries the request
without requesting the extended data, then returns the number of pages
required.
Fixes: fce96cf044308 ("virt: Add SEV-SNP guest driver")
Signed-off-by: Peter Gonda <pgonda@xxxxxxxxxx>
Reported-by: Peter Gonda <pgonda@xxxxxxxxxx>
Cc: Dionna Glaze <dionnaglaze@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Michael Roth <michael.roth@xxxxxxx>
Cc: Haowen Bai <baihaowen@xxxxxxxxx>
Cc: Yang Yingliang <yangyingliang@xxxxxxxxxx>
Cc: Marc Orr <marcorr@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Ashish Kalra <Ashish.Kalra@xxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
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Tested by placing each of the guest requests: attestation quote,
extended attestation quote, and get key. Then tested the extended
attestation quote certificate length querying.
V4
* As suggested by Dionna moved the extended request retry logic into
the driver.
* Due to big change in patch dropped any reviewed-by tags.
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