On Wed, Jan 13, 2021 at 10:11:35AM +0100, Ard Biesheuvel wrote: > Unlike many other structure types defined in the crypto API, the > 'shash_desc' structure is permitted to live on the stack, which > implies its contents may not be accessed by DMA masters. (This is > due to the fact that the stack may be located in the vmalloc area, > which requires a different virtual-to-physical translation than the > one implemented by the DMA subsystem) > > Our definition of CRYPTO_MINALIGN_ATTR is based on ARCH_KMALLOC_MINALIGN, > which may take DMA constraints into account on architectures that support > non-cache coherent DMA such as ARM and arm64. In this case, the value is > chosen to reflect the largest cacheline size in the system, in order to > ensure that explicit cache maintenance as required by non-coherent DMA > masters does not affect adjacent, unrelated slab allocations. On arm64, > this value is currently set at 128 bytes. > > This means that applying CRYPTO_MINALIGN_ATTR to struct shash_desc is both > unnecessary (as it is never used for DMA), and undesirable, given that it > wastes stack space (on arm64, performing the alignment costs 112 bytes in > the worst case, and the hole between the 'tfm' and '__ctx' members takes > up another 120 bytes, resulting in an increased stack footprint of up to > 232 bytes.) So instead, let's switch to the minimum SLAB alignment, which > does not take DMA constraints into account. > > Note that this is a no-op for x86. > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > --- > v3: - drop skcipher_request change again - this needs more careful thought > > v2: - reduce alignment for SYNC_SKCIPHER_REQUEST_ON_STACK as well > - update CRYPTO_MINALIGN_ATTR comment with DMA requirements. > > include/crypto/hash.h | 8 ++++---- > include/linux/crypto.h | 9 ++++++--- > 2 files changed, 10 insertions(+), 7 deletions(-) Patch applied. Thanks. -- Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
