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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id e16-20020a17090301d000b001d337dcc5afsm3718083plh.30.2023.12.13.11.35.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Dec 2023 11:35:06 -0800 (PST) Date: Wed, 13 Dec 2023 11:35:06 -0800 From: Kees Cook To: Wang Cc: Sami Tolvanen , Peter Zijlstra , Aaron Tomlin , Alexander Potapenko , Alexander Shishkin , Alexandru Elisei , Andrew Morton , Anshuman Khandual , Ard Biesheuvel , Arnaldo Carvalho de Melo , Arnd Bergmann , Boqun Feng , Borislav Petkov , Borislav Petkov , Brian Gerst , Catalin Marinas , Changbin Du , Christophe Leroy , Dave Hansen , Dmitry Torokhov , "Eric W. Biederman" , Frederic Weisbecker , gcc-patches@gcc.gnu.org, Greg Kroah-Hartman , "H. Peter Anvin" , Ingo Molnar , Jiri Olsa , Josh Poimboeuf , Juergen Gross , Kalesh Singh , Kumar Kartikeya Dwivedi , Luis Chamberlain , Marco Elver , Mark Brown , Mark Rutland , Masahiro Yamada , Masami Hiramatsu , Michael Roth , Michal Marek , Miguel Ojeda , Namhyung Kim , Nathan Chancellor , Nick Desaulniers , Nicolas Schier , "Paul E. McKenney" , Richard Sandiford , Song Liu , Thomas Gleixner , Tom Rix , Uros Bizjak , Will Deacon , x86@kernel.org, Yuntao Wang , Yu Zhao , Zhen Lei , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev, linux-hardening@vger.kernel.org, linux-arch@vger.kernel.org, linux-modules@vger.kernel.org, linux-perf-users@vger.kernel.org, Dan Li Subject: Re: [RFC/RFT,V2] CFI: Add support for gcc CFI in aarch64 Message-ID: <202312131132.639E8802B@keescook> References: <20221219061758.23321-1-ashimida.1990@gmail.com> <20230325085416.95191-1-ashimida.1990@gmail.com> <20230327093016.GB4253@hirez.programming.kicks-ass.net> <4a84af95-6270-6764-6a40-875ec20fc3e1@lixiang.com> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4a84af95-6270-6764-6a40-875ec20fc3e1@lixiang.com> On Wed, Dec 13, 2023 at 05:01:07PM +0800, Wang wrote: > On 2023/12/13 16:48, Dan Li wrote: > > + Likun > > > > On Tue, 28 Mar 2023 at 06:18, Sami Tolvanen wrote: > >> On Mon, Mar 27, 2023 at 2:30 AM Peter Zijlstra wrote: > >>> On Sat, Mar 25, 2023 at 01:54:16AM -0700, Dan Li wrote: > >>> > >>>> In the compiler part[4], most of the content is the same as Sami's > >>>> implementation[3], except for some minor differences, mainly including: > >>>> > >>>> 1. The function typeid is calculated differently and it is difficult > >>>> to be consistent. > >>> This means there is an effective ABI break between the compilers, which > >>> is sad :-( Is there really nothing to be done about this? > >> I agree, this would be unfortunate, and would also be a compatibility > >> issue with rustc where there's ongoing work to support > >> clang-compatible CFI type hashes: > >> > >> https://github.com/rust-lang/rust/pull/105452 > >> > >> Sami > > > Hi Peter and Sami > > I am Dan Li's colleague, and I will take over and continue the work of CFI. Welcome; this is great news! :) Thanks for picking up the work. > > Regarding the issue of gcc cfi type id being compatible with clang, we > have analyzed and verified: > > 1. clang uses Mangling defined in Itanium C++ ABI to encode the function > prototype, and uses the encoding result as input to generate cfi type id; > 2. Currently, gcc only implements mangling for the C++ compiler, and the > function prototype coding generated by these interfaces is compatible > with clang, but gcc's c compiler does not support mangling.; > > Adding mangling to gcc's c compiler is a huge and difficult task，because > we have to refactor the mangling of C++, splitting it into basic > mangling and language specific mangling, and adding support for the c > language which requires a deep understanding of the compiler and > language processing parts. > > And for the kernel cfi, I suggest separating type compatibility from CFI > basic functions. Type compatibility is independent from CFI basic > funcitons and should be dealt with under another topic. Should we focus > on the main issus of cfi, and  let it work first on linux kernel, and > left the compatible issue to be solved later? If you mean keeping the hashes identical between Clang/LLVM and GCC, I think this is going to be a requirement due to adding Rust to the build environment (which uses the LLVM mangling and hashing). FWIW, I think the subset of type mangling needed isn't the entirely C++ language spec, so it shouldn't be hard to add this to GCC. -Kees -- Kees Cook