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Date: Mon, 1 Nov 2021 00:36:18 +0100 From: Ard Biesheuvel <ardb@...nel.org> To: Peter Zijlstra <peterz@...radead.org> Cc: Sami Tolvanen <samitolvanen@...gle.com>, Mark Rutland <mark.rutland@....com>, X86 ML <x86@...nel.org>, Kees Cook <keescook@...omium.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Sedat Dilek <sedat.dilek@...il.com>, Steven Rostedt <rostedt@...dmis.org>, linux-hardening@...r.kernel.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev Subject: Re: [PATCH] static_call,x86: Robustify trampoline patching On Sun, 31 Oct 2021 at 21:45, Peter Zijlstra <peterz@...radead.org> wrote: > > On Sun, Oct 31, 2021 at 09:21:56PM +0100, Ard Biesheuvel wrote: > > > That means we can support static calls on arm64 now without breaking > > Clang CFI, and work on a solution for the redundant jumps on a more > > relaxed schedule. > > Yes, arm64 has a 'problem' with having already merged the clang-cfi > stuff :/ > > I'm hoping the x86 solution can be an alternative CFI scheme, I'm > starting to really hate this one. And I'm not at all convinced the > proposed scheme is the best possible scheme given the constraints of > kernel code. AFAICT it's a compromise made in userspace. Your scheme only works with IBT: the value of %r11 is under the adversary's control so it could just point it at 'foo+0x10' if it wants to call foo indirectly, and circumvent the check. So without IBT (or BTI), I think the check fundamentally belongs in the caller, not in the callee.
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