This patch removes the build-time test that ensures at least one RNG
is set.  Instead we will simply not build drbg if no options are set
through Kconfig.

This also fixes a typo in the name of the Kconfig option CRYTPO_DRBG
(should be CRYPTO_DRBG).
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

The DRBG-style linked list to manage input data that is fed into the
cipher invocations is replaced with the kernel linked list
implementation.

The change is transparent to users of the interfaces offered by the
DRBG. Therefore, no changes to the testmgr code is needed.
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: NStephan Mueller <smueller@chronox.de>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

For the CTR DRBG, the drbg_state->scratchpad temp buffer (i.e. the
memory location immediately before the drbg_state->tfm variable
is the buffer that the BCC function operates on. BCC operates
blockwise. Making the temp buffer drbg_statelen(drbg) in size is
sufficient when the DRBG state length is a multiple of the block
size. For AES192 this is not the case and the length for temp is
insufficient (yes, that also means for such ciphers, the final
output of all BCC rounds are truncated before used to update the
state of the DRBG!!).

The patch enlarges the temp buffer from drbg_statelen to
drbg_statelen + drbg_blocklen to have sufficient space.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NStephan Mueller <smueller@chronox.de>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

As reported by a static code analyzer, the code for the ordering of
the linked list can be simplified.
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: NStephan Mueller <smueller@chronox.de>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

This is a clean-room implementation of the DRBG defined in SP800-90A.
All three viable DRBGs defined in the standard are implemented:

 * HMAC: This is the leanest DRBG and compiled per default
 * Hash: The more complex DRBG can be enabled at compile time
 * CTR: The most complex DRBG can also be enabled at compile time

The DRBG implementation offers the following:

 * All three DRBG types are implemented with a derivation function.
 * All DRBG types are available with and without prediction resistance.
 * All SHA types of SHA-1, SHA-256, SHA-384, SHA-512 are available for
   the HMAC and Hash DRBGs.
 * All AES types of AES-128, AES-192 and AES-256 are available for the
   CTR DRBG.
 * A self test is implemented with drbg_healthcheck().
 * The FIPS 140-2 continuous self test is implemented.
Signed-off-by: NStephan Mueller <smueller@chronox.de>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>