Re: [PATCH v2] x86, random: Fix get_random_bytes() warning in x86 start_kernel

From: Theodore Y. Ts'o
Date: Mon Feb 04 2019 - 10:55:43 EST

On Sun, Feb 03, 2019 at 08:09:37AM -0500, Prarit Bhargava wrote:
> Ted, the bug I'm trying to fix is the warning:
> random: get_random_bytes called from start_kernel+0x8e/0x587 with crng_init=0
> during early boot. Even with the kernel parameter the warning appears.

Sometimes the warnings are real, and shouldn't be suppressed. A
Debian maintainer once tried to suppress a compile-time warning, and
it was disastrous for security. :-)

What line number is that corresponding to? It sounds like something
is trying to use get_random_bytes() before the random driver was
initialized, and so the first question is does it really need to call
get_random_bytes() then or can it be moved?

> > Also, relying on the TSC for entropy is not something we should be
> > recommending.
> The current code uses the TSC. It is not something new I'm introducing.

But we don't *rely* on it. That's a big difference.

- Ted