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Date: Mon, 16 May 2022 22:37:23 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Sami Tolvanen <samitolvanen@...gle.com> Cc: linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>, Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Joao Moreira <joao@...rdrivepizza.com>, Sedat Dilek <sedat.dilek@...il.com>, Steven Rostedt <rostedt@...dmis.org>, linux-hardening@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev Subject: Re: [RFC PATCH v2 20/21] x86: Add support for CONFIG_CFI_CLANG On Mon, May 16, 2022 at 12:39:19PM -0700, Sami Tolvanen wrote: > > > With the current compiler patch, LLVM sets up function arguments after > > > the CFI check. if it's a problem, we can look into changing that. > > > > Yes, please fix that. Again see that same patch for why this is a > > problem. Objtool can trivially find retpoline calls, but finding this > > kCFI gadget is going to be hard work. If you ensure they're > > unconditionally stuck together, then the problem goes away find one, > > finds the other. > > You can use .kcfi_traps to locate the check right now, but I agree, > it's not quite ideal. Oohh, indeed. Looking at that, I think .kcfi_traps would be better as relative offsets; eg. 'addr = (void*)s + *s' like. Halfs the amount of storage needed for it. Also, that code can use a few {} extra.
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