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From:   Sami Tolvanen <samitolvanen@google.com>
Date:   Fri, 15 Nov 2019 10:34:25 -0800
Message-ID: <CABCJKucsJxXJ6tBYSify-2FS-P1rC=vEKTo+HdhN2e0K9fcBow@mail.gmail.com>
Subject: Re: [PATCH v5 05/14] add support for Clang's Shadow Call Stack (SCS)
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 7:37 AM Mark Rutland <mark.rutland@arm.com> wrote:
> > +config SHADOW_CALL_STACK_VMAP
> > +     bool
> > +     depends on SHADOW_CALL_STACK
> > +     help
> > +       Use virtually mapped shadow call stacks. Selecting this option
> > +       provides better stack exhaustion protection, but increases per-thread
> > +       memory consumption as a full page is allocated for each shadow stack.
>
> The bool needs some display text to make it selectable.
>
> This should probably be below SHADOW_CALL_STACK so that when it shows up
> in menuconfig it's where you'd expect it to be.
>
> I locally hacked that in, but when building defconfig +
> SHADOW_CALL_STACK + SHADOW_CALL_STACK_VMAP, the build explodes as below:

Ugh, thanks for pointing this out. I'll fix this in v6.

Sami