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Message-ID: <CAKwvOdmBcHuhZZV54-76zY60F0Tvd_0DGCi+5dzFTxk0upOYrQ@mail.gmail.com>
Date: Thu, 31 Oct 2019 10:11:16 -0700
From: Nick Desaulniers <ndesaulniers@...gle.com>
To: Sami Tolvanen <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>,
Kees Cook <keescook@...omium.org>, Laura Abbott <labbott@...hat.com>,
Mark Rutland <mark.rutland@....com>, Jann Horn <jannh@...gle.com>,
Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>, LKML <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 9:47 AM <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.
Inline/out-of-line assembly will also need to be careful not to
accidentally overwrite the current task's shadow stack pointer.
Without automated checking for that, we'll have to rely on a
"gentlemen's promise" for code reviewers, though we'd likely hit such
a regression with Android+mainline.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> ---
> 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
>
--
Thanks,
~Nick Desaulniers
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