linux-kernel - Re: [PATCH 07/12] RISC-V: crypto: add Zvkg accelerated GCM GHASH implementation

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Message-ID: <20231122014216.GI2172@sol.localdomain>
Date:   Tue, 21 Nov 2023 17:42:16 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jerry Shih <jerry.shih@...ive.com>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, herbert@...dor.apana.org.au,
        davem@...emloft.net, andy.chiu@...ive.com, greentime.hu@...ive.com,
        conor.dooley@...rochip.com, guoren@...nel.org, bjorn@...osinc.com,
        heiko@...ech.de, ardb@...nel.org, phoebe.chen@...ive.com,
        hongrong.hsu@...ive.com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org
Subject: Re: [PATCH 07/12] RISC-V: crypto: add Zvkg accelerated GCM GHASH
 implementation

On Thu, Oct 26, 2023 at 02:36:39AM +0800, Jerry Shih wrote:
> +struct riscv64_ghash_context {
> +	be128 key;
> +};
> +
> +struct riscv64_ghash_desc_ctx {
> +	be128 shash;
> +	u8 buffer[GHASH_BLOCK_SIZE];
> +	u32 bytes;
> +};

I recommend calling the first struct 'riscv64_ghash_tfm_ctx', and making the
pointers to it be named 'tctx'.  That would more clearly distinguish it from the
desc_ctx / dctx.

> +
> +typedef void (*ghash_func)(be128 *Xi, const be128 *H, const u8 *inp,
> +			   size_t len);
> +
> +static inline void ghash_blocks(const struct riscv64_ghash_context *ctx,
> +				struct riscv64_ghash_desc_ctx *dctx,
> +				const u8 *src, size_t srclen, ghash_func func)
> +	if (crypto_simd_usable()) {
> +		kernel_vector_begin();
> +		func(&dctx->shash, &ctx->key, src, srclen);
> +		kernel_vector_end();

The indirection to ghash_func is unnecessary, since the only value is
gcm_ghash_rv64i_zvkg.

This also means that ghash_update() should be folded into ghash_update_zvkg(),
and ghash_final() into ghash_final_zvkg().

> +	} else {
> +		while (srclen >= GHASH_BLOCK_SIZE) {
> +			crypto_xor((u8 *)&dctx->shash, src, GHASH_BLOCK_SIZE);
> +			gf128mul_lle(&dctx->shash, &ctx->key);
> +			srclen -= GHASH_BLOCK_SIZE;
> +			src += GHASH_BLOCK_SIZE;
> +		}
> +	}

The assembly code uses the equivalent of the following do-while loop instead:

        do {
                srclen -= GHASH_BLOCK_SIZE;
        } while (srclen);

I.e., it assumes the length here is nonzero and a multiple of 16, which it is.

To avoid confusion, I recommend making the C code use the same do-while loop.


>        const struct riscv64_ghash_context *ctx =
>               crypto_tfm_ctx(crypto_shash_tfm(desc->tfm));

crypto_tfm_ctx(crypto_shash_tfm(tfm)) should be crypto_shash_ctx(tfm)

> +static int ghash_final(struct shash_desc *desc, u8 *out, ghash_func func)
> +{
> +	const struct riscv64_ghash_context *ctx =
> +		crypto_tfm_ctx(crypto_shash_tfm(desc->tfm));
> +	struct riscv64_ghash_desc_ctx *dctx = shash_desc_ctx(desc);
> +	int i;
> +
> +	if (dctx->bytes) {
> +		for (i = dctx->bytes; i < GHASH_BLOCK_SIZE; i++)
> +			dctx->buffer[i] = 0;
> +
> +		ghash_blocks(ctx, dctx, dctx->buffer, GHASH_BLOCK_SIZE, func);
> +		dctx->bytes = 0;
> +	}
> +

Setting dctx->bytes above is unnecessary.

> +static int ghash_init(struct shash_desc *desc)
> +{
> +	struct riscv64_ghash_desc_ctx *dctx = shash_desc_ctx(desc);
> +
> +	*dctx = (struct riscv64_ghash_desc_ctx){};
> +
> +	return 0;
> +}
> +
> +static int ghash_update_zvkg(struct shash_desc *desc, const u8 *src,
> +			     unsigned int srclen)
> +{
> +	return ghash_update(desc, src, srclen, gcm_ghash_rv64i_zvkg);
> +}
> +
> +static int ghash_final_zvkg(struct shash_desc *desc, u8 *out)
> +{
> +	return ghash_final(desc, out, gcm_ghash_rv64i_zvkg);
> +}
> +
> +static int ghash_setkey(struct crypto_shash *tfm, const u8 *key,
> +			unsigned int keylen)
> +{
> +	struct riscv64_ghash_context *ctx =
> +		crypto_tfm_ctx(crypto_shash_tfm(tfm));
> +
> +	if (keylen != GHASH_BLOCK_SIZE)
> +		return -EINVAL;
> +
> +	memcpy(&ctx->key, key, GHASH_BLOCK_SIZE);
> +
> +	return 0;
> +}
> +
> +static struct shash_alg riscv64_ghash_alg_zvkg = {
> +	.digestsize = GHASH_DIGEST_SIZE,
> +	.init = ghash_init,
> +	.update = ghash_update_zvkg,
> +	.final = ghash_final_zvkg,
> +	.setkey = ghash_setkey,

IMO it's helpful to order the shash functions as follows, both in their
definitions and their fields in struct shash_alg:

    setkey
    init
    update
    final

That matches the order in which they're called.

- Eric