Re: [PATCH] rust_binder: use AssertSync for BINDER_VM_OPS

["Gary Guo" <gary@garyguo.net>]

On Sat Mar 14, 2026 at 11:19 AM GMT, Alice Ryhl wrote:
> When declaring an immutable global variable in Rust, the compiler checks
> that it looks thread safe, because it is generally safe to access said
> global variable. When using C bindings types for these globals, we don't
> really want this check, because it is conservative and assumes pointers
> are not thread safe.
> 
> In the case of BINDER_VM_OPS, this is a challenge when combined with the
> patch 'userfaultfd: introduce vm_uffd_ops' [1], which introduces a
> pointer field to vm_operations_struct. It previously only held function
> pointers, which are considered thread safe.
> 
> Rust Binder should not be assuming that vm_operations_struct contains no
> pointer fields, so to fix this, use AssertSync (which Rust Binder has
> already declared for another similar global of type struct
> file_operations with the same problem). This ensures that even if
> another commit adds a pointer field to vm_operations_struct, this does
> not cause problems.
> 
> Fixes: 8ef2c15aeae0 ("rust_binder: check ownership before using vma")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202603121235.tpnRxFKO-lkp@intel.com/
> Link: https://lore.kernel.org/r/20260306171815.3160826-8-rppt@kernel.org [1]
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>

Reviewed-by: Gary Guo <gary@garyguo.net>

> ---
>  drivers/android/binder/page_range.rs       | 8 +++++---
>  drivers/android/binder/rust_binder_main.rs | 2 +-
>  2 files changed, 6 insertions(+), 4 deletions(-)