Re: [v2 PATCH] crypto: chacha - Add DEFINE_CHACHA_STATE macro

[Eric Biggers <ebiggers@kernel.org>]

On Tue, Jul 07, 2020 at 08:37:16AM +1000, Herbert Xu wrote:
> On Mon, Jul 06, 2020 at 12:07:17PM -0700, Eric Biggers wrote:
> >
> > This changes chacha_state to be a pointer, which breaks clearing the state
> > because that uses sizeof(chacha_state):
> > 
> > 	memzero_explicit(chacha_state, sizeof(chacha_state));
> > 
> > It would need to be changed to use CHACHA_BLOCK_SIZE.
> 
> Good catch.  Thanks! Here's an update:
> 
> ---8<---
> As it stands the chacha state array is made 12 bytes bigger on
> x86 in order for it to be 16-byte aligned.  However, the array
> is not actually aligned until it hits the x86 code.
> 
> This patch moves the alignment to where the state array is defined.
> To do so a macro DEFINE_CHACHA_STATE has been added which takes
> care of all the work to ensure that it is actually aligned on the
> stack.
> 
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Hmm, __chacha20poly1305_encrypt() already uses:

	memzero_explicit(chacha_state, CHACHA_STATE_WORDS * sizeof(u32));

That's equivalent to CHACHA_BLOCK_SIZE now, but it would be best to use the same
constant everywhere.  Can you pick one or the other to use?

Also, in chacha20poly1305-selftest.c there's a state array that needs to be
converted to use the new macro:

        u32 chacha20_state[CHACHA_STATE_WORDS];

- Eric