linux-kernel - Re: [RFC PATCH 05/28] x86: Define the stack protector guard symbol explicitly

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Message-ID: <CAMzpN2j4uj=mhdi7QHaA7y_NLtaHuRpnit38quK6RjvxdUYQew@mail.gmail.com>
Date: Sat, 28 Sep 2024 09:41:07 -0400
From: Brian Gerst <brgerst@...il.com>
To: Uros Bizjak <ubizjak@...il.com>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org, 
	Ard Biesheuvel <ardb@...nel.org>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
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Subject: Re: [RFC PATCH 05/28] x86: Define the stack protector guard symbol explicitly

On Wed, Sep 25, 2024 at 2:33 PM Uros Bizjak <ubizjak@...il.com> wrote:
>
> On Wed, Sep 25, 2024 at 5:02 PM Ard Biesheuvel <ardb+git@...gle.com> wrote:
> >
> > From: Ard Biesheuvel <ardb@...nel.org>
> >
> > Specify the guard symbol for the stack cookie explicitly, rather than
> > positioning it exactly 40 bytes into the per-CPU area. Doing so removes
> > the need for the per-CPU region to be absolute rather than relative to
> > the placement of the per-CPU template region in the kernel image, and
> > this allows the special handling for absolute per-CPU symbols to be
> > removed entirely.
> >
> > This is a worthwhile cleanup in itself, but it is also a prerequisite
> > for PIE codegen and PIE linking, which can replace our bespoke and
> > rather clunky runtime relocation handling.
>
> I would like to point out a series that converted the stack protector
> guard symbol to a normal percpu variable [1], so there was no need to
> assume anything about the location of the guard symbol.
>
> [1] "[PATCH v4 00/16] x86-64: Stack protector and percpu improvements"
> https://lore.kernel.org/lkml/20240322165233.71698-1-brgerst@gmail.com/
>
> Uros.

I plan on resubmitting that series sometime after the 6.12 merge
window closes.  As I recall from the last version, it was decided to
wait until after the next LTS release to raise the minimum GCC version
to 8.1 and avoid the need to be compatible with the old stack
protector layout.

Brian Gerst