Date: Tue, 1 Oct 2013 22:36:31 -0700 From: Kees Cook <keescook@...omium.org> To: "H. Peter Anvin" <hpa@...or.com> Cc: Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Aaron Durbin <adurbin@...gle.com>, Eric Northup <digitaleric@...gle.com>, Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...gle.com>, Mathias Krause <minipli@...glemail.com>, Zhang Yanfei <zhangyanfei@...fujitsu.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Arnaldo Carvalho de Melo <acme@...radead.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [PATCH v6 0/7] Kernel base address randomization On Tue, Oct 1, 2013 at 10:30 PM, H. Peter Anvin <hpa@...or.com> wrote: > On 10/01/2013 10:25 PM, Ingo Molnar wrote: >> >> I mean, for example in an oops message we print data in words: the RIP, >> other registers and stack contents. If any of these values lies within the >> randomization range then we could de-randomize it. >> >> So instead of exposing randomized values, we could expose de-randomized >> values. >> >> ( This isn't fool-proof: if some data value happens to lie within the >> random range spuriously then we'll incorrectly transform it. In the >> context of oops messages this should not be a big practical problem >> though. ) >> > > I don't agree that this isn't a big practical problem. I often find it > necessary to pick out "things that look like pointers". Overall, > derandomization would make it possible to get really confused when you > have things like half a pointer overwritten. I think reflecting the reality of the system is the correct way to go. Attempting to do the derandomization on the live system seems extremely fragile. It's much cleaner to have a "true" view of the running system and work from there. I don't want to have to wonder if my kernel is lying to me about where things are in memory any more than it already does. :) -Kees -- Kees Cook Chrome OS Security
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