Re: [PATCH -tip] x86/stackprotector: Move stack canary to struct pcpu_hot

[Brian Gerst]

On Fri, Feb 21, 2025 at 9:38 AM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> On Fri, 21 Feb 2025 at 15:33, Uros Bizjak <ubizjak@xxxxxxxxx> wrote:
> >
> > On Fri, Feb 21, 2025 at 3:13 PM Ard Biesheuvel <ardb@xxxxxxxxxx> 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.

Going off on a tangent, as struct pcpu_hot grows I think it can be
done better as a subsection of percpu data (".data..percpu..hot").
That way each variable has its own symbol again and it reduces header
dependencies.


Brian Gerst