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Date: Thu, 29 Aug 2019 12:55:00 -0700
From: Thomas Garnier <>
To: Peter Zijlstra <>
Cc: Borislav Petkov <>, Kernel Hardening <>, 
	Kristen Carlson Accardi <>, Kees Cook <>, 
	Herbert Xu <>, "David S. Miller" <>, 
	Thomas Gleixner <>, Ingo Molnar <>, "H. Peter Anvin" <>, 
	"the arch/x86 maintainers" <>, Andy Lutomirski <>, Juergen Gross <>, 
	Thomas Hellstrom <>, "VMware, Inc." <>, 
	"Rafael J. Wysocki" <>, Len Brown <>, Pavel Machek <>, 
	Nadav Amit <>, Jann Horn <>, Feng Tang <>, 
	Maran Wilson <>, Enrico Weigelt <>, 
	Allison Randal <>, Alexios Zavras <>, 
	Linux Crypto Mailing List <>, LKML <>,, 
	Linux PM list <>
Subject: Re: [PATCH v9 00/11] x86: PIE support to extend KASLR randomization

On Tue, Aug 6, 2019 at 8:51 AM Peter Zijlstra <> wrote:
> On Tue, Aug 06, 2019 at 05:43:47PM +0200, Borislav Petkov wrote:
> > On Tue, Jul 30, 2019 at 12:12:44PM -0700, Thomas Garnier wrote:
> > > These patches make some of the changes necessary to build the kernel as
> > > Position Independent Executable (PIE) on x86_64. Another patchset will
> > > add the PIE option and larger architecture changes.
> >
> > Yeah, about this: do we have a longer writeup about the actual benefits
> > of all this and why we should take this all? After all, after looking
> > at the first couple of asm patches, it is posing restrictions to how
> > we deal with virtual addresses in asm (only RIP-relative addressing in
> > 64-bit mode, MOVs with 64-bit immediates, etc, for example) and I'm
> > willing to bet money that some future unrelated change will break PIE
> > sooner or later.

The goal is being able to extend the range of addresses where the
kernel can be placed with KASLR. I will look at clarifying that in the

> Possibly objtool can help here; it should be possible to teach it about
> these rules, and then it will yell when violated. That should avoid
> regressions.

I will look into that as well.

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