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

[Eric Biggers <ebiggers@kernel.org>]

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