On Wed, Jun 24, 2020 at 05:48:41PM +0200, Ard Biesheuvel wrote: > 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. In the meantime, it is possible to build all the in-tree parts of EFI for BTI, and just turn it off for out-of-tree EFI binaries? If there's no easy way to do this though, I guess we should wait for / push for a PE/COFF flag to describe this properly. Cheers ---Dave
