linux-kernel - Re: [PATCH -tip] x86/stackprotector: Move stack canary to struct pcpu

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Message-ID: <CAMj1kXG_zKei335-CqXwNi=+AkqtQt6xmoVw+qD1XzW7q-aPtA@mail.gmail.com>
Date: Fri, 21 Feb 2025 15:38:44 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Uros Bizjak <ubizjak@...il.com>
Cc: Brian Gerst <brgerst@...il.com>, x86@...nel.org, linux-kernel@...r.kernel.org, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH -tip] x86/stackprotector: Move stack canary to struct pcpu_hot

On Fri, 21 Feb 2025 at 15:33, Uros Bizjak <ubizjak@...il.com> wrote:
>
> On Fri, Feb 21, 2025 at 3:13 PM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> > > > I got a warning from the relocs tool, but not a hard error.  What
> > > > compiler/linker are you using?
> > > >
> > > > Does the attached patch build in your configuration?
> > >
> > > Ah, the attached patch is similar to my previous approach, where the
> > > build system *warned* on an offset (the patch was abandoned due to
> > > Ard's request to put stack_canary to the *beginning* of struct
> > > pcpu_hot, and this allowed for a simplified patch).
> > >
> > > The attached patch builds for me without warning/error for both, SMP
> > > and !SMP build.
> > >
> >
> > Did you try building modules too?
>
> make -j 24 olddefconfig prepare modules_prepare bzImage modules
>
> for defconfig, SMP and !SMP.
>

OK.

I think I prefer Brian's approach - the only nit is that the placement
of stack_canary creates a padding hole in struct pcpu_hot. However,
that does not actually matter until we run out of space so I think it
is fine as is.