On 3/11/24 11:47, Alice Ryhl wrote: > Add safe methods for reading and writing Rust values to and from > userspace pointers. > > The C methods for copying to/from userspace use a function called > `check_object_size` to verify that the kernel pointer is not dangling. > However, this check is skipped when the length is a compile-time > constant, with the assumption that such cases trivially have a correct > kernel pointer. > > In this patch, we apply the same optimization to the typed accessors. > For both methods, the size of the operation is known at compile time to > be size_of of the type being read or written. Since the C side doesn't > provide a variant that skips only this check, we create custom helpers > for this purpose. > > The majority of reads and writes to userspace pointers in the Rust > Binder driver uses these accessor methods. Benchmarking has found that > skipping the `check_object_size` check makes a big difference for the > cases being skipped here. (And that the check doesn't make a difference > for the cases that use the raw read/write methods.) > > This code is based on something that was originally written by Wedson on > the old rust branch. It was modified by Alice to skip the > `check_object_size` check, and to update various comments, including the > notes about kernel pointers in `WritableToBytes`. > > Co-developed-by: Wedson Almeida Filho <wedsonaf@xxxxxxxxx> > Signed-off-by: Wedson Almeida Filho <wedsonaf@xxxxxxxxx> > Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx>
