Re: [PATCH v3 11/16] x86/purgatory: Disable CFI

[Nick Desaulniers]

On Tue, Sep 14, 2021 at 1:30 PM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote:
>
> On Tue, Sep 14, 2021 at 1:02 PM Nick Desaulniers
> <ndesaulniers@xxxxxxxxxx> wrote:
> >
> > On Tue, Sep 14, 2021 at 12:11 PM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote:
> > >
> > > Disable CONFIG_CFI_CLANG for the stand-alone purgatory.ro.
> > >
> > > Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> >
> > I kind of prefer the existing convention that has explicit guards on
> > specific configs (ie. CONFIG_FUNCTION_TRACER, CONFIG_STACKPROTECTOR,
> > CONFIG_STACKPROTECTOR_STRONG, CONFIG_RETPOLINE); it's more obvious
> > which configs may introduce which flags that are problematic. This
> > patch is ok as is, but it kind of makes this Makefile more
> > inconsistent.  I would prefer we had the explicit checks.
>
> The Makefile does already use DISABLE_STACKLEAK_PLUGIN in a similar
> way, but I don't have a strong preference here.

mmm...DISABLE_STACKLEAK_PLUGIN adds to PURGATORY_CFLAGS. This patch
adds to PURGATORY_CFLAGS_REMOVE.

> I can move this into
> an ifdef if it makes things cleaner.
>
> > Does CFI actually do any instrumentation in these object files? I
> > guess issues in purgatory cause silent/hard to debug kexec failures?
>
> The compiler shouldn't add any actual CFI instrumentation here right
> now, but I would prefer to avoid issues in future.

Ok, good to know.
-- 
Thanks,
~Nick Desaulniers