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Message-ID: <ZXnDdooZv0of64ZK@FVFF77S0Q05N> Date: Wed, 13 Dec 2023 14:45:10 +0000 From: Mark Rutland <mark.rutland@....com> To: Wang <wanglikun@...iang.com> Cc: Sami Tolvanen <samitolvanen@...gle.com>, Peter Zijlstra <peterz@...radead.org>, Aaron Tomlin <atomlin@...hat.com>, Alexander Potapenko <glider@...gle.com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Alexandru Elisei <alexandru.elisei@....com>, Andrew Morton <akpm@...ux-foundation.org>, Anshuman Khandual <anshuman.khandual@....com>, Ard Biesheuvel <ardb@...nel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, Arnd Bergmann <arnd@...db.de>, Boqun Feng <boqun.feng@...il.com>, Borislav Petkov <bp@...en8.de>, Borislav Petkov <bp@...e.de>, Brian Gerst <brgerst@...il.com>, Catalin Marinas <catalin.marinas@....com>, Changbin Du <changbin.du@...el.com>, Christophe Leroy <christophe.leroy@...roup.eu>, Dave Hansen <dave.hansen@...ux.intel.com>, Dmitry Torokhov <dmitry.torokhov@...il.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, Frederic Weisbecker <frederic@...nel.org>, gcc-patches@....gnu.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...nel.org>, Josh Poimboeuf <jpoimboe@...nel.org>, Juergen Gross <jgross@...e.com>, Kalesh Singh <kaleshsingh@...gle.com>, Kees Cook <keescook@...omium.org>, Kumar Kartikeya Dwivedi <memxor@...il.com>, Luis Chamberlain <mcgrof@...nel.org>, Marco Elver <elver@...gle.com>, Mark Brown <broonie@...nel.org>, Masahiro Yamada <masahiroy@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, Michael Roth <michael.roth@....com>, Michal Marek <michal.lkml@...kovi.net>, Miguel Ojeda <ojeda@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Nicolas Schier <nicolas@...sle.eu>, "Paul E. McKenney" <paulmck@...nel.org>, Richard Sandiford <richard.sandiford@....com>, Song Liu <song@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Tom Rix <trix@...hat.com>, Uros Bizjak <ubizjak@...il.com>, Will Deacon <will@...nel.org>, x86@...nel.org, Yuntao Wang <ytcoode@...il.com>, Yu Zhao <yuzhao@...gle.com>, Zhen Lei <thunder.leizhen@...wei.com>, linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev, linux-hardening@...r.kernel.org, linux-arch@...r.kernel.org, linux-modules@...r.kernel.org, linux-perf-users@...r.kernel.org, Dan Li <ashimida.1990@...il.com> Subject: Re: [RFC/RFT,V2] CFI: Add support for gcc CFI in aarch64 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. > > 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? I'm not sure what you're suggesting here exactly, do you mean to add a type ID scheme that's incompatible with clang, leaving everything else the same? If so, what sort of scheme are you proposing? It seems unfortunate to have a different scheme, but IIUC we expect all kernel objects to be built with the same compiler. Mark.
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