Date: Fri, 18 Oct 2019 13:33:27 -0700 From: Nick Desaulniers <ndesaulniers@...gle.com> To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com> Cc: Sami Tolvanen <samitolvanen@...gle.com>, 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>, clang-built-linux <clang-built-linux@...glegroups.com>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linux ARM <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 06/18] add support for Clang's Shadow Call Stack (SCS) On Fri, Oct 18, 2019 at 11:33 AM Miguel Ojeda <miguel.ojeda.sandonis@...il.com> wrote: > > On Fri, Oct 18, 2019 at 7:11 PM Sami Tolvanen <samitolvanen@...gle.com> wrote: > > > > On Fri, Oct 18, 2019 at 10:08 AM 'Nick Desaulniers' via Clang Built > > Linux <clang-built-linux@...glegroups.com> wrote: > > > > diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h > > > > index 333a6695a918..9af08391f205 100644 > > > > --- a/include/linux/compiler-clang.h > > > > +++ b/include/linux/compiler-clang.h > > > > @@ -42,3 +42,5 @@ > > > > * compilers, like ICC. > > > > */ > > > > #define barrier() __asm__ __volatile__("" : : : "memory") > > > > + > > > > +#define __noscs __attribute__((no_sanitize("shadow-call-stack"))) > > > > > > It looks like this attribute, (and thus a requirement to use this > > > feature), didn't exist until Clang 7.0: https://godbolt.org/z/p9u1we > > > (as noted above) > > > > > > I think it's better to put __noscs behind a __has_attribute guard in > > > include/linux/compiler_attributes.h. Otherwise, what will happen when > > > Clang 6.0 sees __noscs, for example? (-Wunknown-sanitizers will > > > happen). > > > > Good point, I'll fix this in v2. Thanks. > > +1, please CC whenever you send it! Sami pointed out to me off thread that __has_attribute would only check `no_sanitize`, not `shadow-call-stack`. So maybe best to keep the definition here (include/linux/compiler-clang.h), but wrapped in a `__has_feature` check so that Clang 6.0 doesn't start complaining. -- Thanks, ~Nick Desaulniers
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