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Message-ID: <CAMe9rOrHe9XD2D+pZJrKo1DxkLMQggDOFXQJfTgEO+xp0dybdw@mail.gmail.com> Date: Mon, 26 Sep 2022 13:16:04 -0700 From: "H.J. Lu" <hjl.tools@...il.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Sami Tolvanen <samitolvanen@...gle.com>, 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: [PATCH v5 00/22] KCFI support On Mon, Sep 26, 2022 at 5:39 AM Peter Zijlstra <peterz@...radead.org> wrote: > > On Thu, Sep 08, 2022 at 02:54:42PM -0700, Sami Tolvanen wrote: > > KCFI is a forward-edge control-flow integrity scheme in the upcoming > > Clang 16 release, which is more suitable for kernel use than the > > existing CFI scheme used by CONFIG_CFI_CLANG. KCFI doesn't require > > LTO, doesn't alter function references to point to a jump table, and > > won't break function address equality. > > > > This series replaces the current arm64 CFI implementation with KCFI > > and adds support for x86_64. > > > > KCFI requires assembly functions that are indirectly called from C > > code to be annotated with type identifiers. As type information is > > only available in C, the compiler emits expected type identifiers > > into the symbol table, so they can be referenced from assembly > > without having to hardcode type hashes. Patch 6 adds helper macros > > for annotating functions, and patches 9 and 20 add annotations. > > > > In case of a type mismatch, KCFI always traps. To support error > > handling, the compiler generates a .kcfi_traps section for x86_64, > > which contains the locations of each trap, and for arm64, encodes > > the necessary register information to the ESR. Patches 10 and 22 add > > arch-specific error handlers. > > > > To test this series, you'll need a ToT Clang toolchain. The series > > is also available pn GitHub: > > > > https://github.com/samitolvanen/linux/commits/kcfi-v5 > > As mentioned at plumbers, my only concern is somewhat excessive use of > CFI_CLANG as oposed to something more compiler neutral. But I suppose > that's something we can cleanup/fix when GCC grows support for this. > > Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org> > Tested-by: Peter Zijlstra (Intel) <peterz@...radead.org> > > (as in I ran kCFI + call-depth-tracking + FineIBT on a bunch of > hardware) > > HJL, can you look at adding kCFI support to GCC ? Adding -fsanitize=kcfi to GCC is a big effort. Please open a GCC bug: https://gcc.gnu.org/bugzilla/enter_bug.cgi?product=gcc -- H.J.
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