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Date:   Thu, 16 Jan 2020 17:46:49 +0000
From:   Will Deacon <will@kernel.org>
To:     Sami Tolvanen <samitolvanen@google.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.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@googlegroups.com,
        kernel-hardening@lists.openwall.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 12/15] arm64: vdso: disable Shadow Call Stack
Message-ID: <20200116174648.GE21396@willie-the-truck>
References: <20191018161033.261971-1-samitolvanen@google.com>
 <20191206221351.38241-1-samitolvanen@google.com>
 <20191206221351.38241-13-samitolvanen@google.com>
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On Fri, Dec 06, 2019 at 02:13:48PM -0800, Sami Tolvanen wrote:
> Shadow stacks are only available in the kernel, so disable SCS
> instrumentation for the vDSO.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> ---
>  arch/arm64/kernel/vdso/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> index dd2514bb1511..a87a4f11724e 100644
> --- a/arch/arm64/kernel/vdso/Makefile
> +++ b/arch/arm64/kernel/vdso/Makefile
> @@ -25,7 +25,7 @@ ccflags-y += -DDISABLE_BRANCH_PROFILING
>  
>  VDSO_LDFLAGS := -Bsymbolic
>  
> -CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
> +CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS)

Should we be removing -ffixed-x18 too, or does that not propagate here
anyway?

Will