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Message-ID: <CAKv+Gu-kMzsot5KSPSo_iMsuzcv8J1R5RLT9uGjuzJsxCVUPPg@mail.gmail.com>
Date: Mon, 21 Oct 2019 08:20:43 +0200
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
Steven Rostedt <rostedt@...dmis.org>, Dave Martin <Dave.Martin@....com>,
Kees Cook <keescook@...omium.org>, Laura Abbott <labbott@...hat.com>,
Mark Rutland <mark.rutland@....com>, Nick Desaulniers <ndesaulniers@...gle.com>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 14/18] arm64: efi: restore x18 if it was corrupted
On Fri, 18 Oct 2019 at 18:11, Sami Tolvanen <samitolvanen@...gle.com> wrote:
>
> If we detect a corrupted x18 and SCS is enabled, restore the register
> before jumping back to instrumented code.
>
You'll have to elaborate a bit here and explain that this is
sufficient, given that we run EFI runtime services with interrupts
enabled.
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> ---
> arch/arm64/kernel/efi-rt-wrapper.S | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S
> index 3fc71106cb2b..945744f16086 100644
> --- a/arch/arm64/kernel/efi-rt-wrapper.S
> +++ b/arch/arm64/kernel/efi-rt-wrapper.S
> @@ -34,5 +34,10 @@ ENTRY(__efi_rt_asm_wrapper)
> ldp x29, x30, [sp], #32
> b.ne 0f
> ret
> -0: b efi_handle_corrupted_x18 // tail call
> +0:
> +#ifdef CONFIG_SHADOW_CALL_STACK
> + /* Restore x18 before returning to instrumented code. */
> + mov x18, x2
> +#endif
> + b efi_handle_corrupted_x18 // tail call
> ENDPROC(__efi_rt_asm_wrapper)
> --
> 2.23.0.866.gb869b98d4c-goog
>
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