crypto: drbg - revamp locking

Hi,

the current implementation of the DRBG generates a shadow copy of its DRBG state for each incoming request. The idea is that only a short term lock is needed to spawn the shadow copy. The drawback is that if multiple parallel requests come in, the generated DRBG shadow states only differ by a high-resolution timer that was mixed in during the shadow state generation.

This patch now removes this shadow state and introduces a mutex to serialize all requests to one DRBG instance.

The patch was fully CAVS tested and demonstrates that the DRBG still complies with the standard.

Changes v2:
* fix return code check of drbg_generate in drbg_generate_long
* move mutex_init to drbg_kcapi_init to ensure the mutex is initialized only during the instantiation of a DRBG and during a reset
* merge the patch for replacing the spinlock with a mutex and the removal of the shadow copy generation as both patches cannot stand alone and would therefore break bisection
* drop patch that fixes the memory release (Herbert: you mentioned the patch is applied but it is not yet in the repo -- this patch is vital as otherwise AES192 now breaks without the shadow copy operation)

Changes v3:
* patch for fixing the return code handling in drbg_generate_long did not cover all code paths -- now the issue should be truly fixed

Stephan Mueller (3):
crypto: drbg - fix drbg_generate return val check
crypto: drbg - replace spinlock with mutex
crypto: drbg - leave cipher handles operational

 crypto/drbg.c         | 166 +++++++++++---------------------------------------
 include/crypto/drbg.h |   4 +-
 2 files changed, 36 insertions(+), 134 deletions(-)

2.1.0