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Date: Fri, 18 Oct 2019 10:18:40 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Jann Horn <jannh@...gle.com>
Cc: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
Steven Rostedt <rostedt@...dmis.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>,
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>,
kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 18/18] arm64: implement Shadow Call Stack
On Fri, Oct 18, 2019 at 10:13 AM Jann Horn <jannh@...gle.com> wrote:
> These things should probably be __always_inline or something like
> that? If the compiler decides not to inline them (e.g. when called
> from scs_thread_switch()), stuff will blow up, right?
Correct. I'll change these to __always_inline in v2. I think there
might be other places in the kernel where not inlining a static inline
function would break things, but there's no need to add more.
> This is different from the intended protection level according to
> <https://clang.llvm.org/docs/ShadowCallStack.html#security>, which
> talks about "a runtime that avoids exposing the address of the shadow
> call stack to attackers that can read arbitrary memory". Of course,
> that's extremely hard to implement in the context of the kernel, where
> you can see all the memory management data structures and all physical
> memory.
Yes, the security guarantees in the kernel are different as hiding
shadow stack pointers is more challenging.
> You might want to write something in the cover letter about what the
> benefits of this mechanism compared to STACKPROTECTOR are in the
> context of the kernel, including a specific description of which types
> of attacker capabilities this is supposed to defend against.
Sure, I'll add something about that in v2. Thanks.
Sami
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