From: Kees Cook <keescook@chromium.org>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: linux-kernel@vger.kernel.org, tytso@mit.edu, kees@kernel.org,
linux@armlinux.org.uk, ydroneaud@opteya.com,
gregkh@linuxfoundation.org, rdunlap@infradead.org
Subject: Re: [PATCH v3] random: add helpers for random numbers with given floor or range
Date: Thu, 17 Nov 2022 13:48:14 -0800 [thread overview]
Message-ID: <202211171347.92FDE65A6D@keescook> (raw)
In-Reply-To: <20221117192620.2304613-1-Jason@zx2c4.com>
On Thu, Nov 17, 2022 at 08:26:20PM +0100, Jason A. Donenfeld wrote:
> Now that we have get_random_u32_below(), it's nearly trivial to make
> inline helpers to compute get_random_u32_above() and
> get_random_u32_inclusive(), which will help clean up open coded loops
> and manual computations throughout the tree.
>
> One snag is that in order to make get_random_u32_inclusive() operate on
> closed intervals, we have to do some (unlikely) special case handling if
> get_random_u32_interval(0, U32_MAX) is called. The least expensive way
> of doing this is actually to adjust the slowpath of
> get_random_u32_below() to have its undefined 0 result just return the
> output of get_random_u32(). We can make this basically free by calling
> get_random_u32() before the branch, so that the branch latency gets
> interleaved.
>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
I really like these -- unambiguous! :) Thanks for adjusting this API.
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
--
Kees Cook
prev parent reply other threads:[~2022-11-17 21:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-17 16:35 [PATCH v2] random: add helpers for random numbers with given floor or range Jason A. Donenfeld
2022-11-17 16:41 ` Randy Dunlap
2022-11-17 19:26 ` [PATCH v3] " Jason A. Donenfeld
2022-11-17 21:48 ` Kees Cook [this message]
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