linux-kernel - Re: [PATCH v2] random: tie batched entropy generation to base

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Date:   Sun, 20 Feb 2022 20:13:51 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [PATCH v2] random: tie batched entropy generation to base_crng
 generation

On Thu, Feb 10, 2022 at 02:13:04PM +0100, Jason A. Donenfeld wrote:
> Now that we have an explicit base_crng generation counter, we don't need
> a separate one for batched entropy. Rather, we can just move the
> generation forward every time we change crng_init state or update the
> base_crng key.
> 
> Cc: Theodore Ts'o <tytso@....edu>
> Reviewed-by: Dominik Brodowski <linux@...inikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
> v2 always increments the generation after extraction, as suggested by
> Dominik.
> 
>  drivers/char/random.c | 29 ++++++++---------------------
>  1 file changed, 8 insertions(+), 21 deletions(-)

Reviewed-by: Eric Biggers <ebiggers@...gle.com>

One comment below:

> @@ -455,7 +453,7 @@ static size_t crng_fast_load(const void *cp, size_t len)
>  		src++; crng_init_cnt++; len--; ret++;
>  	}
>  	if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
> -		invalidate_batched_entropy();
> +		++base_crng.generation;
>  		crng_init = 1;
>  	}

This is an existing issue, but why doesn't crng_slow_load() do this too?

- Eric