linux-kernel - Re: [PATCH 3/3] vsprintf: Add use-early-random-bytes cmd line option

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Date:   Tue, 1 May 2018 21:45:07 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     tcharding <me@...in.cc>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Theodore Ts'o <tytso@....edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 3/3] vsprintf: Add use-early-random-bytes cmd line
 option

On Wed, 2 May 2018 11:27:58 +1000
tcharding <me@...in.cc> wrote:

> On Wed, May 02, 2018 at 01:02:34AM +0000, Linus Torvalds wrote:
> > On Tue, May 1, 2018 at 4:34 PM Tobin C. Harding <me@...in.cc> wrote:
> > 
> >   
> > > This option should NOT be enabled on production kernels.  
> > 
> > I think with your fixes to get_random_bytes_arch(), it's perfectly fine to
> > use on production kernels (and doesn't even need a kernel command line
> > option).
> > 
> > It was only with the "use weak crypto" (that get_random_bytes_arch() used
> > to fall back on) that it was a problem. That fixed "verify that
> > get_random_bytes_arch() really uses hw crypto" is certainly not weak crypto.  

Except for where hardware vendors control what random bytes you
actually get ;-)

> 
> Ok, I'll wait to see if anyone with a more paranoid disposition adds to
> this otherwise will implement as suggested.

I still test on a lot of old boxes (my old workstations turn into my
test boxes). I haven't tried to see which machines have RDRAND support.
But regardless, can we still have a command line option that forces
early randomization even if RDRAND isn't supported?

-- Steve