Re: [PATCH v3 3/9] efi/libstub: Remove .note.gnu.property

[Ard Biesheuvel]

On Wed, 24 Jun 2020 at 17:45, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Wed, Jun 24, 2020 at 05:31:06PM +0200, Ard Biesheuvel wrote:
> > On Wed, 24 Jun 2020 at 17:21, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > >
> > > On Wed, Jun 24, 2020 at 12:46:32PM +0200, Ard Biesheuvel wrote:
> > > > I'm not sure if there is a point to having PAC and/or BTI in the EFI
> > > > stub, given that it runs under the control of the firmware, with its
> > > > memory mappings and PAC configuration etc.
> > >
> > > Is BTI being ignored when the firmware runs?
> >
> > Given that it requires the 'guarded' attribute to be set in the page
> > tables, and the fact that the UEFI spec does not require it for
> > executables that it invokes, nor describes any means of annotating
> > such executables as having been built with BTI annotations, I think we
> > can safely assume that the EFI stub will execute with BTI disabled in
> > the foreseeable future.
>
> yaaaaaay. *sigh* How long until EFI catches up?
>
> That said, BTI shouldn't _hurt_, right? If EFI ever decides to enable
> it, we'll be ready?
>

Sure. Although I anticipate that we'll need to set some flag in the
PE/COFF header to enable it, and so any BTI opcodes we emit without
that will never take effect in practice.