Challenge proposal: NonNull (#52)

doc/src/SUMMARY.md

@@ -18,5 +18,6 @@
   - [Pointer Arithmetic](./challenges/0003-pointer-arithmentic.md)
   - [Memory safety of BTreeMap's `btree::node` module](./challenges/0004-btree-node.md)
   - [Inductive data type](./challenges/0005-linked-list.md)
+  - [Safety of NonNull](./challenges/0006-nonnull.md)
   - [Contracts for SmallSort](./challenges/0008-smallsort.md)
   - [Memory safety of String](./challenges/0010-string.md)

doc/src/challenges/0006-nonnull.md

@@ -0,0 +1,84 @@
+# Challenge 6: Safety of NonNull
+
+- **Status:** Open
+- **Tracking Issue:** [Link to issue](https://github.com/model-checking/verify-rust-std/issues/53)
+- **Start date:** *2024-08-16*
+- **End date:** *2024-12-10*
+
+-------------------
+
+
+## Goal
+
+Verify absence of undefined behavior of the [`ptr::NonNull` module](https://github.com/rust-lang/rust/blob/master/library/core/src/ptr/non_null.rs).
+Most of its functions are marked `unsafe`, yet they are used in 62 other modules
+of the standard library.
+
+### Success Criteria
+
+Prove absence of undefined behavior of the following 48 public functions. You
+may wish to do so by attaching pre- and postconditions to these, and then (if
+needed by the tooling that you choose to use) adding verification harnesses.
+
+1. `NonNull<T>::add`
+2. `NonNull<T>::addr`
+3. `NonNull<T>::align_offset`
+4. `NonNull<T>::as_mut<'a>`
+5. `NonNull<T>::as_mut_ptr`
+6. `NonNull<T>::as_non_null_ptr`
+7. `NonNull<T>::as_ptr`
+8. `NonNull<T>::as_ref<'a>`
+9. `NonNull<T>::as_uninit_mut<'a>`
+10. `NonNull<T>::as_uninit_ref<'a>`
+11. `NonNull<T>::as_uninit_slice<'a>`
+12. `NonNull<T>::as_uninit_slice_mut<'a>`
+13. `NonNull<T>::byte_add`
+14. `NonNull<T>::byte_offset_from<U: ?Sized>`
+15. `NonNull<T>::byte_offset`
+16. `NonNull<T>::byte_sub`
+17. `NonNull<T>::cast<U>`
+18. `NonNull<T>::copy_from_nonoverlapping`
+19. `NonNull<T>::copy_from`
+20. `NonNull<T>::copy_to_nonoverlapping`
+21. `NonNull<T>::copy_to`
+22. `NonNull<T>::dangling`
+23. `NonNull<T>::drop_in_place`
+24. `NonNull<T>::from_raw_parts`
+25. `NonNull<T>::get_unchecked_mut<I>`
+26. `NonNull<T>::is_aligned_to`
+27. `NonNull<T>::is_aligned`
+28. `NonNull<T>::is_empty`
+29. `NonNull<T>::len`
+30. `NonNull<T>::map_addr`
+31. `NonNull<T>::new_unchecked`
+32. `NonNull<T>::new`
+33. `NonNull<T>::offset_from`
+34. `NonNull<T>::offset`
+35. `NonNull<T>::read_unaligned`
+36. `NonNull<T>::read_volatile`
+37. `NonNull<T>::read`
+38. `NonNull<T>::replace`
+39. `NonNull<T>::slice_from_raw_parts`
+40. `NonNull<T>::sub_ptr`
+41. `NonNull<T>::sub`
+42. `NonNull<T>::swap`
+43. `NonNull<T>::to_raw_parts`
+44. `NonNull<T>::with_addr`
+45. `NonNull<T>::write_bytes`
+46. `NonNull<T>::write_unaligned`
+47. `NonNull<T>::write_volatile`
+48. `NonNull<T>::write`
+
+### List of UBs
+
+In addition to any properties called out as `SAFETY` comments in the source
+code,
+all proofs must automatically ensure the absence of the following [undefined behaviors](https://github.com/rust-lang/reference/blob/142b2ed77d33f37a9973772bd95e6144ed9dce43/src/behavior-considered-undefined.md):
+
+* Accessing (loading from or storing to) a place that is dangling or based on a misaligned pointer.
+* Reading from uninitialized memory.
+* Mutating immutable bytes.
+* Producing an invalid value
+
+Note: All solutions to verification challenges need to satisfy the criteria established in the [challenge book](../general-rules.md)
+in addition to the ones listed above.