linux-kernel - Re: [PATCH v2] crypto: x86/polyval - Fix crashes when keys are not 16-byte aligned

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Date:   Tue, 18 Oct 2022 15:39:24 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Nathan Huckleberry <nhuck@...gle.com>
Cc:     herbert@...dor.apana.org.au, ardb@...nel.org, bgoncalv@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, davem@...emloft.net,
        hpa@...or.com, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
        x86@...nel.org
Subject: Re: [PATCH v2] crypto: x86/polyval - Fix crashes when keys are not
 16-byte aligned

On Tue, Oct 18, 2022 at 02:56:23PM -0700, Nathan Huckleberry wrote:
> -static void internal_polyval_update(const struct polyval_tfm_ctx *keys,
> +static inline struct polyval_tfm_ctx *polyval_tfm_ctx(const void *raw_ctx)
> +{
> +	unsigned long addr = (unsigned long)raw_ctx;
> +	unsigned long align = POLYVAL_ALIGN;
> +
> +	if (align <= crypto_tfm_ctx_alignment())
> +		align = 1;
> +	return (struct polyval_tfm_ctx *)ALIGN(addr, align);
> +}

This could just use PTR_ALIGN.  Also, checking for POLYVAL_ALIGN <=
crypto_tfm_ctx_alignment() isn't necessary.

> +
> +static void internal_polyval_update(const void *raw_keys,
>  	const u8 *in, size_t nblocks, u8 *accumulator)
>  {
> +	const struct polyval_tfm_ctx *keys = polyval_tfm_ctx(raw_keys);

This is being passed a struct polyval_tfm_ctx.  There's no need to cast it back
to a void pointer and align it again redundantly.

>  	if (likely(crypto_simd_usable())) {
>  		kernel_fpu_begin();
>  		clmul_polyval_update(keys, in, nblocks, accumulator);
> @@ -102,7 +117,8 @@ static int polyval_x86_update(struct shash_desc *desc,
>  			 const u8 *src, unsigned int srclen)
>  {
>  	struct polyval_desc_ctx *dctx = shash_desc_ctx(desc);
> -	const struct polyval_tfm_ctx *tctx = crypto_shash_ctx(desc->tfm);
> +	const struct polyval_tfm_ctx *tctx =
> +	    polyval_tfm_ctx(crypto_shash_ctx(desc->tfm));
>  	u8 *pos;
>  	unsigned int nblocks;
>  	unsigned int n;

It would make more sense to have the polyval_tfm_ctx() function take in the
struct crypto_shash.

How about using the following:

static inline struct polyval_tfm_ctx *polyval_tfm_ctx(struct crypto_shash *tfm)
{
        return PTR_ALIGN(crypto_shash_ctx(tfm), POLYVAL_ALIGN);
}

- Eric