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Date:   Tue, 29 May 2018 11:19:25 -0700
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Subject: Re: [PATCH] x86, random: Fix get_random_bytes() warning in x86 start_kernel
To:     Prarit Bhargava <prarit@redhat.com>,
        "Theodore Y. Ts'o" <tytso@mit.edu>,
        Kees Cook <keescook@chromium.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, X86 ML <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>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Kate Stewart <kstewart@linuxfoundation.org>
From:   hpa@zytor.com
Message-ID: <54FF298C-0992-4592-AAF8-9ABBF8DE917D@zytor.com>
Sender: linux-kernel-owner@vger.kernel.org
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On May 29, 2018 9:58:10 AM PDT, Prarit Bhargava <prarit@redhat.com> wrote:
>
>
>On 05/29/2018 12:07 PM, Theodore Y. Ts'o wrote:
>> On Tue, May 29, 2018 at 11:01:07AM -0400, Prarit Bhargava wrote:
>>> Kees, in early boot no pool is available so the stack canary is
>initialized from
>>> the TSC.  Later in boot, the stack canary will use the the crng.
>>>
>>> ie) in early boot only TSC is okay, and late boot (when crng_ready()
>is true)
>>> the pool will be used.
>> 
>> But that means all of the kernel threads (e.g., workqueues, et. al)
>> would not be well protected by the stack canary.  That
>> seems.... rather unfortunate.
>
>Well, as stated the TSC is used as a source of entropy in early boot. 
>It's
>always been that way and get_random_bytes() AFAICT has always returned
>0.  CPUs
>added later on via hotplug do use get_random_bytes().
>
>Does anyone cc'd have a better idea on how to get another source of
>entropy this
>early in boot?
>
>P.
>
>> 
>>       	     	  	      	   	     - Ted
>> 

RDRAND/RDSEED for newer x86 processors.
-- 
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