linux-kernel - Re: [PATCH] random: Move rand

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Date:   Fri, 12 Oct 2018 07:45:44 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Theodore Y. Ts'o" <tytso@....edu>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Laura Abbott <labbott@...hat.com>,
        Daniel Micay <danielmicay@...il.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Tobin C. Harding" <me@...in.cc>, Arnd Bergmann <arnd@...db.de>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] random: Move rand_initialize() earlier

On Fri, Oct 12, 2018 at 7:29 AM, Theodore Y. Ts'o <tytso@....edu> wrote:
> On Thu, Oct 11, 2018 at 03:54:21PM -0700, Kees Cook wrote:
>> Right now rand_initialize() is run as an early_initcall(), but it only
>> depends on timekeeping_init() (for mixing ktime_get_real() into the
>> pools). However, the call to boot_init_stack_canary() for stack canary
>> initialization runs earlier, which triggers a warning at boot:
>>
>> random: get_random_bytes called from start_kernel+0x357/0x548 with crng_init=0
>>
>> Instead, this moves rand_initialize() to after timekeeping_init(), and moves
>> canary initialization here as well.
>>
>> Note that this warning may still remain for machines that do not have
>> UEFI RNG support (which initializes the RNG pools durting setup_arch()),
>> or for x86 machines without RDRAND (or booting without "random.trust=on"
>> or CONFIG_RANDOM_TRUST_CPU=y).
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>
> This seems reasonable to me.  Were you hoping to get this in for -rc8?
> It looks sane, and I don't see any _obvious_ unintended consequences
> of such a change, but it's rather late in the development cycle, and
> it isn't regression fix.

Yeah, for sure. I didn't mean this for 4.19. I assumed -next, and
likely further changes based on discussion, etc etc.

-Kees

-- 
Kees Cook
Pixel Security