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

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Date:   Wed, 20 Jun 2018 19:30:50 +0000
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Kees Cook <keescook@...omium.org>,
        Herbert Xu <herbert@...dor.apana.org.au>
Cc:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Alasdair Kergon <agk@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Biggers <ebiggers@...gle.com>,
        Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
        Lars Persson <larper@...s.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Rabin Vincent <rabinv@...s.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, qat-linux@...el.com,
        dm-devel@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/11] crypto: shash: Remove VLA usage



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@...omium.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
>   
>   /**
>