From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Prarit Bhargava <prarit@redhat.com>
Cc: <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
<x86@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Rik van Riel <riel@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Philippe Ombredanne <pombredanne@nexb.com>,
Kees Cook <keescook@chromium.org>,
"Jason A. Donenfeld" <Jason@zx2c4.com>,
Kate Stewart <kstewart@linuxfoundation.org>
Subject: Re: [PATCH v2] x86, random: Fix get_random_bytes() warning in x86 start_kernel
Date: Fri, 1 Feb 2019 22:02:40 -0500 [thread overview]
Message-ID: <20190202030240.GA9802@mit.edu> (raw)
In-Reply-To: <20190201180831.19839-1-prarit@redhat.com>
On Fri, Feb 01, 2019 at 01:08:31PM -0500, Prarit Bhargava wrote:
> After 43838a23a05f ("random: fix crng_ready() test") early boot calls to
> get_random_bytes() will warn on x86 because the crng is not initialized.
> For example,
>
> random: get_random_bytes called from start_kernel+0x8e/0x587 with crng_init=0
>
> x86 only uses get_random_bytes() for better randomization of the stack
> canary value so the warning is of no consequence.
>
> Test if the crng is initialized before calling get_random_bytes(). If it
> is not available then attempt to read from the hardware random generator,
> before finally using the TSC.
If you want to trust the CPU's hardware number generator, there is a
way to do this already. Simply enable CONFIG_RANDOM_TRUST_CPU, or set
the boot command line option "random.trust_cpu=on".
Also, relying on the TSC for entropy is not something we should be
recommending.
So, NAK.
- Ted
next prev parent reply other threads:[~2019-02-02 3:02 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-01 18:08 [PATCH v2] x86, random: Fix get_random_bytes() warning in x86 start_kernel Prarit Bhargava
2019-02-02 3:02 ` Theodore Y. Ts'o [this message]
2019-02-03 13:09 ` Prarit Bhargava
2019-02-04 15:55 ` Theodore Y. Ts'o
2019-02-08 13:14 ` Prarit Bhargava
2019-02-08 17:43 ` Theodore Y. Ts'o
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