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From:   Sami Tolvanen <samitolvanen@google.com>
Date:   Fri, 15 Nov 2019 12:19:20 -0800
Message-ID: <CABCJKudm28QaKRxPHWgKuEfRvm=EvuUEmcAVOnNkbxBCJcYX5A@mail.gmail.com>
Subject: Re: [PATCH v5 14/14] arm64: implement Shadow Call Stack
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        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>,
        LKML <linux-kernel@vger.kernel.org>
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On Fri, Nov 15, 2019 at 7:20 AM Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Tue, Nov 05, 2019 at 03:56:08PM -0800, Sami Tolvanen wrote:
> > This change implements shadow stack switching, initial SCS set-up,
> > and interrupt shadow stacks for arm64.
>
> Each CPU also has an overflow stack, and two SDEI stacks, which should
> presumably be given their own SCS. SDEI is effectively a software-NMI,
> so it should almost certainly have the same treatement as IRQ.

Makes sense. I'll take a look at adding shadow stacks for the SDEI handler.

> Can we please fold this comment into the one above, and have:
>
>         /*
>          * The callee-saved regs (x19-x29) should be preserved between
>          * irq_stack_entry and irq_stack_exit.
>          */
>         .macro irq_stack_exit
>         mov     sp, x19
> #ifdef CONFIG_SHADOW_CALL_STACK
>         mov     x18, x20
> #endif
>         .endm

Sure, I'll change this in the next version.

Sami