linux-kernel - Re: [PATCH] x86, random: Fix get_random_bytes() warning in x86 start

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Message-ID: <35cdbb04-7b1d-59ae-2ff8-af1d57751113@redhat.com>
Date:   Tue, 29 May 2018 12:58:10 -0400
From:   Prarit Bhargava <prarit@...hat.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rik van Riel <riel@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Kate Stewart <kstewart@...uxfoundation.org>
Subject: Re: [PATCH] x86, random: Fix get_random_bytes() warning in x86
 start_kernel



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
>