On Tue Mar 18, 2025 at 1:29 PM CET, Alice Ryhl wrote: > On Mon, Mar 17, 2025 at 10:23:56AM -0400, Tamir Duberstein wrote: >> Throughout the tree, use the strict provenance APIs stabilized in Rust >> 1.84.0[1]. Retain backwards-compatibility by introducing forwarding >> functions at the `kernel` crate root along with polyfills for rustc < >> 1.84.0. >> >> Use `#[allow(clippy::incompatible_msrv)]` to avoid warnings on rustc < >> 1.84.0 as our MSRV is 1.78.0. >> >> In the `kernel` crate, enable the strict provenance lints on rustc >= >> 1.84.0; do this in `lib.rs` rather than `Makefile` to avoid introducing >> compiler flags that are dependent on the rustc version in use. >> >> Link: https://blog.rust-lang.org/2025/01/09/Rust-1.84.0.html#strict-provenance-apis [1] >> Suggested-by: Benno Lossin <benno.lossin@xxxxxxxxx> >> Link: https://lore.kernel.org/all/D8EIXDMRXMJP.36TFCGWZBRS3Y@xxxxxxxxx/ >> Signed-off-by: Tamir Duberstein <tamird@xxxxxxxxx> > > I'm not convinced that the pros of this change outweigh the cons. I > think this is going to be too confusing for the C developers who look at > this code. 1) I think we should eliminate all possible `as` conversions. They are non-descriptive (since they can do may *very* different things) and ptr2int conversions are part of that. 2) At some point we will have to move to the provenance API, since that's what Rust chose to do. I don't think that doing it at a later point is doing anyone a favor. 3) I don't understand the argument that this is confusing to C devs. They are just normal functions that are well-documented (and if that's not the case, we can just improve them upstream). And functions are much easier to learn about than `as` casts (those are IMO much more difficult to figure out than then strict provenance functions). Thus I think we should keep this patch (with Boqun's improvement). >> diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs >> index 719b0a48ff55..96393bcf6bd7 100644 >> --- a/rust/kernel/uaccess.rs >> +++ b/rust/kernel/uaccess.rs >> @@ -226,7 +226,9 @@ pub fn read_raw(&mut self, out: &mut [MaybeUninit<u8>]) -> Result { >> } >> // SAFETY: `out_ptr` points into a mutable slice of length `len`, so we may write >> // that many bytes to it. >> - let res = unsafe { bindings::copy_from_user(out_ptr, self.ptr as *const c_void, len) }; >> + let res = unsafe { >> + bindings::copy_from_user(out_ptr, crate::with_exposed_provenance(self.ptr), len) >> + }; >> if res != 0 { >> return Err(EFAULT); >> } >> @@ -264,7 +266,7 @@ pub fn read<T: FromBytes>(&mut self) -> Result<T> { >> let res = unsafe { >> bindings::_copy_from_user( >> out.as_mut_ptr().cast::<c_void>(), >> - self.ptr as *const c_void, >> + crate::with_exposed_provenance(self.ptr), >> len, >> ) >> }; > > That's especially true for cases like this. These are userspace pointers > that are never dereferenced. It's not useful to care about provenance > here. I agree for this case, but I think we shouldn't be using raw pointers for this to begin with. I'd think that a newtype wrapping `usize` is a much better fit. It can then also back the `IoRaw` type. AFAIU user space pointers don't have provenance, right? (if they do, then we should use this API :) --- Cheers, Benno
