On Wed, Jun 20, 2018 at 12:04:06PM -0700, Kees Cook wrote: > In the quest to remove all stack VLA usage from the kernel[1], this uses > the newly defined max alignment to perform unaligned hashing to avoid > VLAs, and drops the helper function while adding sanity checks on the > resulting buffer sizes. > > [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@xxxxxxxxxxxxxx > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- > crypto/shash.c | 21 ++++++++++----------- > 1 file changed, 10 insertions(+), 11 deletions(-) > > diff --git a/crypto/shash.c b/crypto/shash.c > index ab6902c6dae7..1bb58209330a 100644 > --- a/crypto/shash.c > +++ b/crypto/shash.c > @@ -73,13 +73,6 @@ int crypto_shash_setkey(struct crypto_shash *tfm, const u8 *key, > } > EXPORT_SYMBOL_GPL(crypto_shash_setkey); > > -static inline unsigned int shash_align_buffer_size(unsigned len, > - unsigned long mask) > -{ > - typedef u8 __aligned_largest u8_aligned; > - return len + (mask & ~(__alignof__(u8_aligned) - 1)); > -} > - > static int shash_update_unaligned(struct shash_desc *desc, const u8 *data, > unsigned int len) > { > @@ -88,11 +81,14 @@ static int shash_update_unaligned(struct shash_desc *desc, const u8 *data, > unsigned long alignmask = crypto_shash_alignmask(tfm); > unsigned int unaligned_len = alignmask + 1 - > ((unsigned long)data & alignmask); > - u8 ubuf[shash_align_buffer_size(unaligned_len, alignmask)] > - __aligned_largest; > + u8 ubuf[CRYPTO_ALG_MAX_ALIGNMASK] > + __aligned(CRYPTO_ALG_MAX_ALIGNMASK + 1); > u8 *buf = PTR_ALIGN(&ubuf[0], alignmask + 1); > int err; Are you sure that __attribute__((aligned(64))) works correctly on stack variables on all architectures? And if it is expected to work, then why is the buffer still aligned by hand on the very next line? > > + if (WARN_ON(buf + unaligned_len > ubuf + sizeof(ubuf))) > + return -EINVAL; > + > if (unaligned_len > len) > unaligned_len = len; > > @@ -124,11 +120,14 @@ static int shash_final_unaligned(struct shash_desc *desc, u8 *out) > unsigned long alignmask = crypto_shash_alignmask(tfm); > struct shash_alg *shash = crypto_shash_alg(tfm); > unsigned int ds = crypto_shash_digestsize(tfm); > - u8 ubuf[shash_align_buffer_size(ds, alignmask)] > - __aligned_largest; > + u8 ubuf[SHASH_MAX_DIGESTSIZE] > + __aligned(CRYPTO_ALG_MAX_ALIGNMASK + 1); > u8 *buf = PTR_ALIGN(&ubuf[0], alignmask + 1); > int err; Same questions here. > > + if (WARN_ON(buf + ds > ubuf + sizeof(ubuf))) > + return -EINVAL; > + > err = shash->final(desc, buf); > if (err) > goto out; > -- - Eric
