From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Martin Subject: Re: [PATCH v3 3/9] efi/libstub: Remove .note.gnu.property Date: Wed, 24 Jun 2020 17:29:19 +0100 Message-ID: <20200624162919.GH25945@arm.com> References: <20200624014940.1204448-1-keescook@chromium.org> <20200624014940.1204448-4-keescook@chromium.org> <20200624033142.cinvg6rbg252j46d@google.com> <202006232143.66828CD3@keescook> <20200624104356.GA6134@willie-the-truck> <202006240820.A3468F4@keescook> <202006240844.7BE48D2B5@keescook> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from foss.arm.com ([217.140.110.172]:40744 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404976AbgFXQ30 (ORCPT ); Wed, 24 Jun 2020 12:29:26 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Ard Biesheuvel Cc: Kees Cook , Mark Rutland , linux-arch , linux-efi , Arnd Bergmann , Fangrui Song , Peter Collingbourne , Catalin Marinas , Masahiro Yamada , X86 ML , Nick Desaulniers , Russell King , Linux Kernel Mailing List , clang-built-linux , Arvind Sankar , Ingo Molnar , James Morse , Thomas Gleixner , Borislav Petkov , Will Deacon On Wed, Jun 24, 2020 at 05:48:41PM +0200, Ard Biesheuvel wrote: > On Wed, 24 Jun 2020 at 17:45, Kees Cook wrote: > > > > On Wed, Jun 24, 2020 at 05:31:06PM +0200, Ard Biesheuvel wrote: > > > On Wed, 24 Jun 2020 at 17:21, Kees Cook 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.110.172]:40744 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404976AbgFXQ30 (ORCPT ); Wed, 24 Jun 2020 12:29:26 -0400 Date: Wed, 24 Jun 2020 17:29:19 +0100 From: Dave Martin Subject: Re: [PATCH v3 3/9] efi/libstub: Remove .note.gnu.property Message-ID: <20200624162919.GH25945@arm.com> References: <20200624014940.1204448-1-keescook@chromium.org> <20200624014940.1204448-4-keescook@chromium.org> <20200624033142.cinvg6rbg252j46d@google.com> <202006232143.66828CD3@keescook> <20200624104356.GA6134@willie-the-truck> <202006240820.A3468F4@keescook> <202006240844.7BE48D2B5@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Ard Biesheuvel Cc: Kees Cook , Mark Rutland , linux-arch , linux-efi , Arnd Bergmann , Fangrui Song , Peter Collingbourne , Catalin Marinas , Masahiro Yamada , X86 ML , Nick Desaulniers , Russell King , Linux Kernel Mailing List , clang-built-linux , Arvind Sankar , Ingo Molnar , James Morse , Thomas Gleixner , Borislav Petkov , Will Deacon , Nathan Chancellor , Linux ARM Message-ID: <20200624162919.Gx7jfTj4MsF32B3dqfgAZBE5GvyaovHl_pIZaZXmvHY@z> On Wed, Jun 24, 2020 at 05:48:41PM +0200, Ard Biesheuvel wrote: > On Wed, 24 Jun 2020 at 17:45, Kees Cook wrote: > > > > On Wed, Jun 24, 2020 at 05:31:06PM +0200, Ard Biesheuvel wrote: > > > On Wed, 24 Jun 2020 at 17:21, Kees Cook 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