On Thu, Oct 12, 2023 at 11:31 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > On Thu, Oct 12, 2023 at 10:50:36AM -0700, Sami Tolvanen wrote: > > On Thu, Oct 12, 2023 at 3:47 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > > > On Fri, Oct 14, 2022 at 11:34:30AM -0700, Sami Tolvanen wrote: > > > > On Fri, Oct 14, 2022 at 11:05 AM Miguel Ojeda > > > > <miguel.ojeda.sandonis@xxxxxxxxx> wrote: > > > > > > > > > > On Tue, Oct 11, 2022 at 1:16 AM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote: > > > > > > > > > > > > Rust supports IBT with -Z cf-protection=branch, but I don't see this > > > > > > option being enabled in the kernel yet. Cross-language CFI is going to > > > > > > require a lot more work though because the type systems are not quite > > > > > > compatible: > > > > > > > > > > > > https://github.com/rust-lang/rfcs/pull/3296 > > > > > > > > > > I have pinged Ramon de C Valle as he is the author of the RFC above > > > > > and implementation work too; since a month or so ago he also leads the > > > > > Exploit Mitigations Project Group in Rust. > > > > > > > > Thanks, Miguel. I also talked to Ramon about KCFI earlier this week > > > > and he expressed interest in helping with rustc support for it. In the > > > > meanwhile, I think we can just add a depends on !CFI_CLANG to avoid > > > > issues here. > > > > > > Having just read up on the thing it looks like the KCFI thing is > > > resolved. > > > > > > I'm not sure I understand most of the objections in that thread through > > > -- enabling CFI *will* break stuff, so what. > > > > > > Squashing the integer types seems a workable compromise I suppose. One > > > thing that's been floated in the past is adding a 'seed' attribute to > > > some functions in order to distinguish functions of otherwise identical > > > signature. > > > > > > The Rust thing would then also need to support this attribute. > > > > > > Are there any concrete plans for this? It would allow, for example, > > > to differentiate address_space_operations::swap_deactivate() from any > > > other random function that takes only a file argument, say: > > > locks_remove_file(). > > > > I haven't really had time to look into it, so no concrete plans yet. > > Adding an attribute shouldn't be terribly difficult, but Kees > > expressed interest in automatic salting as well, which might be a more > > involved project: > > > > https://github.com/ClangBuiltLinux/linux/issues/1736 > > Automatic would be nice, but having an attribute would let us at least > start the process manually (or apply salting from static analysis > output, etc). An idea would be to add something like the Rust cfi_encoding attribute[1] and use it with something similar to the Newtype Pattern[2], but in C[3], for aggregating function pointers that otherwise would be aggregated in the same group in different groups. [1]: https://doc.rust-lang.org/nightly/unstable-book/language-features/cfi-encoding.html [2]: https://doc.rust-lang.org/book/ch19-04-advanced-types.html#using-the-newtype-pattern-for-type-safety-and-abstraction [3]: Wrapping a type in a struct should achieve something similar even without using the cfi_encoding attribute since the encoding for structs is <length><name>, where <name> is <unscoped-name>.
