Messages in this thread | | | From | Matthew Maurer <> | Date | Tue, 10 Oct 2023 07:34:45 -0700 | Subject | Re: [PATCH] x86: Enable IBT in Rust if enabled in C |
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On Tue, Oct 10, 2023 at 7:24 AM Peter Zijlstra <peterz@infradead.org> wrote: > > On Tue, Oct 10, 2023 at 07:06:32AM -0700, Matthew Maurer wrote: > > > > > +KBUILD_RUSTFLAGS += -Zcf-protection=branch -Zno-jump-tables > > > > > > One question, -Zcf-protection=branch, will that ever emit NOTRACK > > > prefix? The kernel very explicitly does not support (enable) NOTRACK. > > > rustc does this via LLVM, so its code generation works very similarly to clang. > > It does not create its own explicit NOTRACKs, but LLVM will by default > > with just -Zcf-protection-branch. > > I've linked a godbolt showing that at least for the basic case, your > > no-jump-tables approach from clang ports over. > > https://godbolt.org/z/bc4n6sq5q > > Whether rust generates NOTRACK should end up being roughly equivalent > > to whether clang generates it, and if LLVM gains a code generation > > flag for NOTRACK being disallowed some day, we can pass that through > > as well. > > IIRC C++ will also emit NOTRACK for things like catch/throw and other > stack/scope unwinds. Obviously C doesn't have that, but does Rust? (as > might be obvious, I *really* don't know the language). > That's fine - Rust does have stack/scope unwinds with the `panic=unwind` strategy. In the kernel, we use `panic=abort` and are unlikely to ever change this approach. There are a host of other complications that come from unwinding without NOTRACK getting involved :)
In case you find `catch_unwind` - this function only has an effect with `panic=unwind`. When `panic=abort`, there's nothing analogous to catch/throw anymore, and `catch_unwind` becomes a no-op.
Are there other features you expect might trigger NOTRACK? > ISTR HJL had a GCC patch to force-disable NOTRACK, but I've no idea what > happened to that. >
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