Re: [PATCH 01/11] crypto: shash: Remove VLA usage

Christophe Leroy
2018-06-20T20:09:54Z

On 06/20/2018 07:03 PM, Kees Cook wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> removes the VLAs in SHASH_DESC_ON_STACK (via crypto_shash_descsize())
> by using the maximum allowable size (which is now more clearly captured
> in a macro). Similar limits are turned into macros as well.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@chromium.org>

Got the following warnings:

crypto/testmgr.c: In function ‘alg_test_crc32c.part.4’:
crypto/testmgr.c:1896:1: warning: the frame size of 2088 bytes is larger
than 1024 bytes [-Wframe-larger-than=]
crypto/hmac.c: In function ‘hmac_setkey’:
crypto/hmac.c:88:1: warning: the frame size of 2088 bytes is larger than
1024 bytes [-Wframe-larger-than=]

Christophe

> ---
> crypto/shash.c | 6 +++---
> include/crypto/hash.h | 6 +++++-
> 2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/crypto/shash.c b/crypto/shash.c
> index 5d732c6bb4b2..ab6902c6dae7 100644
> --- a/crypto/shash.c
> +++ b/crypto/shash.c
> @@ -458,9 +458,9 @@ static int shash_prepare_alg(struct shash_alg *alg)
> {
> struct crypto_alg *base = &alg->base;
>
> - if (alg->digestsize > PAGE_SIZE / 8 ||
> - alg->descsize > PAGE_SIZE / 8 ||
> - alg->statesize > PAGE_SIZE / 8)
> + if (alg->digestsize > SHASH_MAX_DIGESTSIZE ||
> + alg->descsize > SHASH_MAX_DESCSIZE ||
> + alg->statesize > SHASH_MAX_STATESIZE)
> return -EINVAL;
>
> base->cra_type = &crypto_shash_type;
> diff --git a/include/crypto/hash.h b/include/crypto/hash.h
> index 76e432cab75d..308aad8bf523 100644
> --- a/include/crypto/hash.h
> +++ b/include/crypto/hash.h
> @@ -151,9 +151,13 @@ struct shash_desc {
> void *__ctx[] CRYPTO_MINALIGN_ATTR;
> };
>
> +#define SHASH_MAX_DIGESTSIZE (PAGE_SIZE / 8)
> +#define SHASH_MAX_DESCSIZE (PAGE_SIZE / 8)
> +#define SHASH_MAX_STATESIZE (PAGE_SIZE / 8)
> +
> #define SHASH_DESC_ON_STACK(shash, ctx) \
> char __##shash##_desc[sizeof(struct shash_desc) + \
> - crypto_shash_descsize(ctx)] CRYPTO_MINALIGN_ATTR; \
> + SHASH_MAX_DESCSIZE] CRYPTO_MINALIGN_ATTR; \
> struct shash_desc *shash = (struct shash_desc *)__##shash##_desc
>
> /**
>