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

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Date:   Wed, 24 Jun 2020 17:31:06 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Will Deacon <will@...nel.org>, Fangrui Song <maskray@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        James Morse <james.morse@....com>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>, X86 ML <x86@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/9] efi/libstub: Remove .note.gnu.property

On Wed, 24 Jun 2020 at 17:21, Kees Cook <keescook@...omium.org> 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.