tree 612b6a5c8233d074f7c63de6228c3c69f9c9d7e5
parent 37335af9c5488ed349271a8ba9ff209c940a5e2c
author Andrey Pronin <apronin@google.com> 1627052566 +0300
committer Commit Bot <commit-bot@chromium.org> 1628214649 +0000

tpm2: don't assert on policy sessions in IsAuthValueAvailable

This CL fixes the incorrect assert in IsAuthValueAvailable.
Before the fix, the code was doing
  pAssert(!IsPolicySessionRequired(commandCode, sessionIndex));
assuming that we can and should never come to this point with
policy session, since entities requiring policy sessions can't
have authValues. This is wrong on two accounts:
1) nv indices have authVaues, but e.g. NV_ChangeAuth requires
ADMIN auth, and thus policy session, for the affected nv index;
2) it is possible to call IsAuthValueAvailable() with policy session
if the policy session is also used as an encrypt/decrypt session
(which is allowed): in ParseSessionBuffer(), when it starts decrypting
the 1st parameter, if s_decryptSessionIndex != UNDEFINED_INDEX and
s_associatedHandles[s_decryptSessionIndex] != TPM_RH_UNASSIGNED,
IsAuthValueAvailable() is called regarless the type of the session.

This error is fixed in TPM reference code on github.com/microsoft/ms-tpm-20-ref
since at least rev 1.38:
https://github.com/microsoft/ms-tpm-20-ref/blob/b8e599267381badbe0571f8ace55b28a5f16457c/TPMCmd/tpm/src/main/SessionProcess.c#L295

See also item 2.12 in TPM 2.0 rev 1.16 errata:
https://trustedcomputinggroup.org/wp-content/uploads/TPM2.0-Library-Spec-v1.16-Errata_v1.5_09212016.pdf

BUG=none
TEST=NV_ChangeAuth with a single auth+encrypt+decrypt session

Change-Id: Id0abcac078c76918254595b749e5d4aed919b74a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/tpm2/+/3048088
Tested-by: Andrey Pronin <apronin@chromium.org>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
Commit-Queue: Mary Ruthven <mruthven@chromium.org>