On Sat, Jan 07, 2023 at 07:42:13AM -0800, Dan Li wrote: > Hi Kees, > > On 01/06, Kees Cook wrote: > > On Mon, Dec 19, 2022 at 05:32:04AM -0800, Dan Li wrote: > > > Hi Peter, > > Hi! > > > > First of all, thank you thank you for working on this in GCC. This will > > make a big difference for folks that don't have the option to build with > > Clang to gain CFI coverage. > > > > As for the implementation details, the core issue is really that this > > type of CFI is specifically designed for the Linux kernel, and it took a > > rather long time to figure out all the specifics needed (down to the > > byte counts and instruction layouts). GCC's version will ultimately need > > to exactly match the Clang output, or Linux is unlikely to support it. > > > > We're already on our second CFI -- the original Clang CFI was just too > > clunky for long-term use in Linux, so unless we're going to improve on > > the latest Clang KCFI implementation in some way, it's better to stick > > to exactly byte-for-byte identical results. The KCFI support in Linux > > depends on the arm64 and x86_64 runtimes for catching the traps, and the > > post-processing done (on x86_64) with objtool that prepares the kernel > > for IBT use, and converts to the optional FineIBT CFI mechanism. With > > all those moving parts, there needs to be a very compelling reason to > > have GCC KCFI implementation differ from Clang's. > > > > Hopefully that context helps a little. I'm excited to try out future > > versions! > > Thanks for the context, it makes sense and helped me a lot. :) > > In the next version I'll make the gcc implementation consistent with clang. Hi! Just checking in on this, since there are a lot of interested folks. :) What's the status on the next version (and has anyone been found to tackle the x86 backend part)? Is there anything we can help with? Thanks! -Kees -- Kees Cook
