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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