linux-kernel - Re: [RESEND] SHASH_DESC_ON

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Message-ID: <20180327100709.GA12961@gondor.apana.org.au>
Date:   Tue, 27 Mar 2018 18:07:09 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND] SHASH_DESC_ON_STACK macro

On Fri, Mar 23, 2018 at 02:09:46PM -0500, Gustavo A. R. Silva wrote:
> 
> Hi Herbert,
> 
> There is an ongoing effort to remove all VLAs from the code base [1] and
> while working on that I came across the following macro at
> include/crypto/hash.h:154:
> 
> #define SHASH_DESC_ON_STACK(shash, ctx)                           \
>         char __##shash##_desc[sizeof(struct shash_desc) +         \
>                 crypto_shash_descsize(ctx)] CRYPTO_MINALIGN_ATTR; \
>         struct shash_desc *shash = (struct shash_desc *)__##shash##_desc
> 
> 
> Currently, this macro is being used in 46 different places.
> 
> I wonder how big can tfm->descsize can get?

descsize is capped at PAGE_SIZE / 8.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt