linux-kernel - Re: [PATCH 07/12] random: use the arch-specific rng in xfer_secondary

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Date:	Sun, 08 Jul 2012 02:06:46 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	ewust@...ch.edu, zakir@...ch.edu, nadiah@...ucsd.edu,
	jhalderm@...ch.edu, stable@...r.kernel.org
Subject: Re: [PATCH 07/12] random: use the arch-specific rng in
 xfer_secondary_pool

On Fri, 2012-07-06 at 18:44 -0400, Theodore Ts'o wrote:
> If the CPU supports a hardware random number generator, use it in
> xfer_secondary_pool(), where it will significantly improve things and
> where we can afford it.
> 
> Also, remove the use of the arch-specific rng in
> add_timer_randomness(), since the call is significantly slower than
> get_cycles(), and we're much better off using it in
> xfer_secondary_pool() anyway.
[...]
> @@ -838,7 +834,11 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
>   */
>  static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
>  {
> -	__u32 tmp[OUTPUT_POOL_WORDS];
> +	union {
> +		__u32	tmp[OUTPUT_POOL_WORDS];
> +		long	hwrand[4];
> +	} u;
> +	int	i;
[...]
> +	for (i = 0; i < 4; i++)
> +		if (arch_get_random_long(&u.hwrand[i]))
> +			break;
> +	if (i)
> +		mix_pool_bytes(r, &u.hwrand, sizeof(u.hwrand), 0);
[...]

Surely the number of random bytes being added is i * sizeof(long), not
sizeof(u.hwrand)?

Ben.

-- 
Ben Hutchings
Life would be so much easier if we could look at the source code.

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