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Date: Thu, 31 Oct 2019 20:59:58 -0700
From: Kees Cook <keescook@...omium.org>
To: samitolvanen@...gle.com
Cc: Will Deacon <will@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Dave Martin <Dave.Martin@....com>,
Laura Abbott <labbott@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Jann Horn <jannh@...gle.com>,
Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
clang-built-linux@...glegroups.com,
kernel-hardening@...ts.openwall.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 12/17] arm64: reserve x18 from general allocation with
SCS
On Thu, Oct 31, 2019 at 09:46:32AM -0700, samitolvanen@...gle.com wrote:
> Reserve the x18 register from general allocation when SCS is enabled,
> because the compiler uses the register to store the current task's
> shadow stack pointer. Note that all external kernel modules must also be
> compiled with -ffixed-x18 if the kernel has SCS enabled.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
> arch/arm64/Makefile | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 2c0238ce0551..ef76101201b2 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -72,6 +72,10 @@ stack_protector_prepare: prepare0
> include/generated/asm-offsets.h))
> endif
>
> +ifeq ($(CONFIG_SHADOW_CALL_STACK), y)
> +KBUILD_CFLAGS += -ffixed-x18
> +endif
> +
> ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
> KBUILD_CPPFLAGS += -mbig-endian
> CHECKFLAGS += -D__AARCH64EB__
> --
> 2.24.0.rc0.303.g954a862665-goog
>
--
Kees Cook
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