Date: Fri, 5 Apr 2013 10:04:18 +0200 From: Ingo Molnar <mingo@...nel.org> To: "H. Peter Anvin" <hpa@...or.com> Cc: Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, x86@...nel.org, Jarkko Sakkinen <jarkko.sakkinen@...el.com>, Matthew Garrett <mjg@...hat.com>, Matt Fleming <matt.fleming@...el.com>, Eric Northup <digitaleric@...gle.com>, Dan Rosenberg <drosenberg@...curity.com>, Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...omium.org>, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: [PATCH 3/3] x86: kernel base offset ASLR * H. Peter Anvin <hpa@...or.com> wrote: > I have to admit to being somewhat skeptical toward KASLR with only 8 > bits of randomness. There are at least two potential ways of > dramatically increasing the available randomness: > > 1. actually compose the kernel of multiple independently relocatable > pieces (maybe chunk it on 2M boundaries or something.) > > 2. compile the kernel as one of the memory models which can be executed > anywhere in the 64-bit address space. The cost of this would have > to be quantified, of course. > > The latter is particularly something that should be considered for the > LPF JIT, to defend against JIT spray attacks. The cost of 64-bit RIPs is probably measurable both in cache footprint and in execution speed. Doing that might make sense - but unless it's surprisingly cheap to do it, at least from a distro perspective, randomizing the kernel base using the existing compact address space would probably be the preferred option - even if a bigger build model was available. Random runtime shuffling of the kernel image - is that possible with existing toolchains? Thanks, Ingo
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