Re: [PATCH net-next v2 2/5] net/tcp-ao: Use crypto library API instead of crypto_ahash

David Laight
2026-04-28T01:24:48Z

On Mon, 27 Apr 2026 10:27:24 -0700
Eric Biggers <ebiggers@kernel.org> wrote:

> Currently the kernel's TCP-AO implementation does the MAC and KDF
> computations using the crypto_ahash API. This API is inefficient and
> difficult to use, and it has required extensive workarounds in the form
> of per-CPU preallocated objects (tcp_sigpool) to work at all.
>
> Let's use lib/crypto/ instead. This means switching to straightforward
> stack-allocated structures, virtually addressed buffers, and direct
> function calls. It also means removing quite a bit of error handling.
> This makes TCP-AO quite a bit faster.
>
> This also enables many additional cleanups, which later commits will
> handle: removing tcp-sigpool, removing support for crypto_tfm cloning,
> removing more error handling, and replacing more dynamically-allocated
> buffers with stack buffers based on the now-statically-known limits.
>
> Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
> Signed-off-by: Eric Biggers <ebiggers@kernel.org>
...
> @@ -344,33 +444,26 @@ static int tcp_v4_ao_calc_key(struct tcp_ao_key *mkt, u8 *key,
> struct kdf_input_block {
> u8 counter;
> u8 label[6];
> struct tcp4_ao_context ctx;
> __be16 outlen;
> - } __packed * tmp;

That looks a bit horrid.
I also had a feeling that the compiler sometimes rejects non-packed structures
inside packed ones.
Perhaps nest the whole thing inside another structure that has an initial
u8 pad and is marked __packed __aligned(4).
Then the assignments to the fields of 'ctx' will be known to be aligned
even when tcp4_ao_context is also __packed.

David

> - struct tcp_sigpool hp;
> - int err;
> -
> - err = tcp_sigpool_start(mkt->tcp_sigpool_id, &hp);
> - if (err)
> - return err;
> -
> - tmp = hp.scratch;
> - tmp->counter = 1;
> - memcpy(tmp->label, "TCP-AO", 6);
> - tmp->ctx.saddr = saddr;
> - tmp->ctx.daddr = daddr;
> - tmp->ctx.sport = sport;
> - tmp->ctx.dport = dport;
> - tmp->ctx.sisn = sisn;
> - tmp->ctx.disn = disn;
> - tmp->outlen = htons(tcp_ao_digest_size(mkt) * 8); /* in bits */
> -
> - err = tcp_ao_calc_traffic_key(mkt, key, tmp, sizeof(*tmp), &hp);
> - tcp_sigpool_end(&hp);
> -
> - return err;
> + } __packed input = {
> + .counter = 1,
> + .label = "TCP-AO",
> + .ctx = {
> + .saddr = saddr,
> + .daddr = daddr,
> + .sport = sport,
> + .dport = dport,
> + .sisn = sisn,
> + .disn = disn,
> + },
> + .outlen = htons(tcp_ao_digest_size(mkt) * 8), /* in bits */
> + };
> +
> + tcp_ao_calc_traffic_key(mkt, key, &input, sizeof(input));
> + return 0;
> }