[PATCH v3 0/1] crypto: ccp - Make sev_cmd_mutex more granular

[Michael Roth <michael.roth@amd.com>]

This patchset is also available at:

  https://github.com/amdese/linux/commits/ccp-mutex-rework-v3

and is based on cryptodev-2.6 master (178aff4cf425).

v1: https://lore.kernel.org/linux-crypto/20261014132145.1726322-1-michael.roth@amd.com/
v2: https://lore.kernel.org/linux-crypto/20261016041109.1778673-1-michael.roth@amd.com/
v3:
 - drop all unnecessary refactorings to make patches more appropriate for 7.4
   (Herbert, Sean)
 - retest CCP both with and without kvm/queue in-place conversion support
   present, re-verify no deadlocks/regressions. Testing done primarilly with
   the following kselftest:
     https://github.com/AMDESE/linux/commit/33ddcbd756b3db5bd2bd5737e48c9084e715cd38
 - rebase on latest cryptodev master (178aff4cf425)


OVERVIEW
--------

The current code makes very coarse usage of the sev_cmd_mutex; for SEV
firmware ioctls, it is essentially taken upon entry, and ends up wrapping
a lot of potentially time-consuming prep/cleanup work that may need to be
done before/after issuing the actual firmware call, which is the main
thing the mutex is meant to protect.

Additionally, some of that prep work involves
copy_from_user()/copy_to_user() calls which can generate page faults and
unecessarily lead to potential deadlock scenarios. No known case exists
in current upstream, but with the upcoming KVM/guest_memfd support for
in-place conversion of the same PFN between shared/private state (which
is currently targeted for kernel 7.4), a special fault handler is added
that could theoretically deadlock if a malicious user tries to use
guest_memfd pages as the source/target of target of said
copy_from_user()/copy_to_user() scenarios[1].

So this series is a prereq to enabling the above-mentioned KVM/guest_memfd
in-place conversion support on SNP-enabled hosts, as well as a cleanup
for SEV ioctls in general.

Thank you to Sean for suggesting this approach and Ackerley for wrangling
the changes into a (hopefully) presentable patchset.


REFERENCES
----------

[1] https://lore.kernel.org/kvm/asz8GKNO9aQANr5E@google.com/


Thanks!

-Mike


----------------------------------------------------------------
Michael Roth (1):
      crypto: ccp - Make usage of sev_cmd_mutex more granular

 drivers/crypto/ccp/sev-dev.c | 101 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 76 insertions(+), 25 deletions(-)