From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755068AbeD3Q5t (ORCPT ); Mon, 30 Apr 2018 12:57:49 -0400 Received: from mail-io0-f171.google.com ([209.85.223.171]:33288 "EHLO mail-io0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754772AbeD3Q5s (ORCPT ); Mon, 30 Apr 2018 12:57:48 -0400 X-Google-Smtp-Source: AB8JxZobd51smjkakACvExm/VXSVStQ0Pq7rcDwPGJDvyjcLu5Iy7A8e3WxOdUgDBFj9urVlfLwROW0KPHAFQMeJHwQ= MIME-Version: 1.0 References: <20180430124135.0cce92e3@gandalf.local.home> In-Reply-To: <20180430124135.0cce92e3@gandalf.local.home> From: Linus Torvalds Date: Mon, 30 Apr 2018 16:57:36 +0000 Message-ID: Subject: Re: Hashed pointer issues To: Steven Rostedt Cc: Kees Cook , Anna-Maria Gleixner , Linux Kernel Mailing List , tcharding Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Archived-At: List-Archive: List-Post: On Mon, Apr 30, 2018 at 9:41 AM Steven Rostedt wrote: > > > > And if we really want a command line option, can we make that still hash > > the pointer, just force the entropy early. That way kernel developers that > > test that command line option are still testing the *hashing*, they just > > are missing the good entropy. > That may work too. Even with bad entropy, pointers at start up are hard > to come by, and I can't see a hacker being able to use them as it only > happens once during boot. No, if people use the command line option, *all* pointers - not just the boot-time ones - would get cryptographically bad hashes, since you don't want to change the hash once it's picked (because then you couldn't use the hashing to identify objects). So the boot command line wouldn't affect just the bootup hashing, it would be bad at runtime too. But at least a person booting with that option would get the same *behavior* as everybody else, and they wouldn't be testing something fundamnetally different (it's still hashing, just not cryptographically strong). Although in *practice* we'd have tons of entropy on any modern development CPU too, since any new hardware will have the hardware random number generation. Some overly cautious person might not trust it, of course. Linus