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Date:   Mon, 26 Sep 2022 09:22:41 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        stable@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH] random: split initialization into early arch step and
 later non-arch step
Message-Id: <20220926092241.64f73e7420cea6b964f1f116@linux-foundation.org>
In-Reply-To: <20220926160332.1473462-1-Jason@zx2c4.com>
References: <20220926160332.1473462-1-Jason@zx2c4.com>
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On Mon, 26 Sep 2022 18:03:32 +0200 "Jason A. Donenfeld" <Jason@zx2c4.com> wrote:

> The full RNG initialization relies on some timestamps, made possible
> with general functions like time_init() and timekeeping_init(). However,
> these are only available rather late in initialization. Meanwhile, other
> things, such as memory allocator functions, make use of the RNG much
> earlier.
> 
> So split RNG initialization into two phases. We can give arch randomness
> very early on, and then later, after timekeeping and such are available,
> initialize the rest.
> 
> This ensures that, for example, slabs are properly randomized if RDRAND
> is available. Another positive consequence is that on systems with
> RDRAND, running with CONFIG_WARN_ALL_UNSEEDED_RANDOM=y results in no
> warnings at all.

Please give a full description of the user-visible runtime effects of
this shortcoming.

> Cc: Kees Cook <keescook@chromium.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: stable@vger.kernel.org

Which is important when proposing a -stable backport.