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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Tue, 7 Apr 2020 14:00:12 +0200
Message-ID: <CAKv+Gu9psVBSdUvcRWNrEvjK4ckyA-vGKmZ33O2NUm-Pt4eJig@mail.gmail.com>
Subject: Re: [PATCH v10 12/12] efi/libstub: disable SCS
To:     Sami Tolvanen <samitolvanen@google.com>
Cc:     Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        James Morse <james.morse@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Kees Cook <keescook@chromium.org>,
        Laura Abbott <labbott@redhat.com>,
        Marc Zyngier <maz@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Jann Horn <jannh@google.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, 6 Apr 2020 at 18:42, Sami Tolvanen <samitolvanen@google.com> wrote:
>
> Shadow stacks are not available in the EFI stub, filter out SCS flags.
>
> Suggested-by: James Morse <james.morse@arm.com>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

Acked-by: Ard Biesheuvel <ardb@kernel.org>

> ---
>  drivers/firmware/efi/libstub/Makefile | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 094eabdecfe6..fa0bb64f93d6 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -32,6 +32,9 @@ KBUILD_CFLAGS                 := $(cflags-y) -DDISABLE_BRANCH_PROFILING \
>                                    $(call cc-option,-fno-stack-protector) \
>                                    -D__DISABLE_EXPORTS
>
> +#  remove SCS flags from all objects in this directory
> +KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
> +
>  GCOV_PROFILE                   := n
>  KASAN_SANITIZE                 := n
>  UBSAN_SANITIZE                 := n
> --
> 2.26.0.292.g33ef6b2f38-goog
>