[0/3] crypto: adjust meaning of CRYPTO_ALG_ALLOCATES_MEMORY

Message

Cabiddu, Giovanni July 5, 2023, 4:40 p.m. UTC

Commit fbb6cda44190 introduced the flag CRYPTO_ALG_ALLOCATES_MEMORY.
This allows to mark algorithms that allocate memory during the datapath
so they are not used for disk encryption.
Following that, cd74693870fb limited dm-crypt to use only
implementations that don't set that flag.

After discussions in the crypto mailing list [1][2][3] about how we
could re-enable algorithms to be used by dm-crypt, we came to the
conclusion that we can change slightly the meaning of the flag
!CRYPTO_ALG_ALLOCATES_MEMORY. If an algorithm does not allocate
memory for requests with a scatterlist of 4 or less entries
(the typical case for dm-crypt), then it can avoid marking the
implementation with the flag CRYPTO_ALG_ALLOCATES_MEMORY.

This set adjusts the meaning of CRYPTO_ALG_ALLOCATES_MEMORY in the
documentation, removes the filtering for algorithms that do not
allocate memory in dm-integrity and removes the
CRYPTO_ALG_ALLOCATES_MEMORY from the algorithms registered in the QAT
driver as this is not allocating memory in the datapath for requests
with 4 or less entries in the source and destination scatterlists.

[1] https://lore.kernel.org/linux-crypto/[e-mail]/
[2] https://lore.kernel.org/linux-crypto/[e-mail]/
[3] https://lore.kernel.org/linux-crypto/Ysw9E2Az2oK4jfCf@lucas-Virtual-Machine/

Giovanni Cabiddu (3):
  dm integrity: do not filter algos with CRYPTO_ALG_ALLOCATES_MEMORY
  crypto: api - adjust meaning of CRYPTO_ALG_ALLOCATES_MEMORY
  crypto: qat - remove CRYPTO_ALG_ALLOCATES_MEMORY flag

 drivers/crypto/intel/qat/qat_common/qat_algs.c | 13 ++++++-------
 .../intel/qat/qat_common/qat_comp_algs.c       |  2 +-
 drivers/md/dm-integrity.c                      |  2 +-
 include/linux/crypto.h                         | 18 ++++++++++++++++--
 4 files changed, 24 insertions(+), 11 deletions(-)

Comments

Cabiddu, Giovanni July 5, 2023, 8:57 p.m. UTC | #1

Thanks Eric.

On Wed, Jul 05, 2023 at 01:12:05PM -0700, Eric Biggers wrote:
> On Wed, Jul 05, 2023 at 05:40:07PM +0100, Giovanni Cabiddu wrote:
> > The flag CRYPTO_ALG_ALLOCATES_MEMORY indicates that an algorithm might
> > allocate memory in the datapath and therefore sleep.
> > Dm-integrity is filtering out implementations of skcipher algorithms
> > that have this flag set. However, in the same function it does
> > allocations with GFP_KERNEL.
> 
> Which function is the above referring to?  The actual encryption/decryption
> happens in crypt_journal(), and I don't see any memory allocations there.
You are right. I was referring to create_journal() which is allocating
memory right before calling do_crypt().
However, I didn't consider crypt_journal() which might not be allocating
memory before calling do_crypt().

Then we are then back to square one. We need to check how many entries
are present in the scatterlists encrypted by crypt_journal() before
adjusting the meaning of !CRYPTO_ALG_ALLOCATES_MEMORY.

Regards,