Contracts & Harnesses for add, addr, and align_offset
#105
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zhassan-aws
reviewed
Oct 8, 2024
| @@ -279,6 +279,8 @@ impl<T: ?Sized> NonNull<T> { | |||
| #[must_use] | |||
| #[inline] | |||
| #[unstable(feature = "strict_provenance", issue = "95228")] | |||
| #[requires(!self.as_ptr().is_null())] | |||
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This requires clause is not needed since this is an invariant of this type.
| @@ -279,6 +279,8 @@ impl<T: ?Sized> NonNull<T> { | |||
| #[must_use] | |||
| #[inline] | |||
| #[unstable(feature = "strict_provenance", issue = "95228")] | |||
| #[requires(!self.as_ptr().is_null())] | |||
| #[ensures(|result| result.get() != 0)] | |||
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I think this can be strengthened to result.get() == self.as_ptr() as usize.
| @@ -560,6 +566,8 @@ impl<T: ?Sized> NonNull<T> { | |||
| // Additionally safety contract of `offset` guarantees that the resulting pointer is | |||
| // pointing to an allocation, there can't be an allocation at null, thus it's safe to | |||
| // construct `NonNull`. | |||
| assert!(core::mem::size_of::<T>() == 1, "element size is 1"); | |||
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This assert and the next one were added as part of our debugging of the failure in offset and should now be removed.
| @@ -552,6 +554,10 @@ impl<T: ?Sized> NonNull<T> { | |||
| #[must_use = "returns a new pointer rather than modifying its argument"] | |||
| #[stable(feature = "non_null_convenience", since = "1.80.0")] | |||
| #[rustc_const_stable(feature = "non_null_convenience", since = "1.80.0")] | |||
| #[requires(count.checked_mul(core::mem::size_of::<T>()).is_some())] // Prevent offset overflow | |||
| #[requires(count * core::mem::size_of::<T>() <= isize::MAX as usize)] // SAFETY: count * size_of::<T>() does not overflow isize | |||
| //#[requires(ub_checks::can_write(self.as_ptr().offset(count as isize)))] // not working | |||
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As mentioned in #99 (comment), the solution is to combine this requires clause with the count.checked_mul one to make sure they're properly applied.
| @@ -1177,6 +1185,37 @@ impl<T: ?Sized> NonNull<T> { | |||
| #[must_use] | |||
| #[stable(feature = "non_null_convenience", since = "1.80.0")] | |||
| #[rustc_const_unstable(feature = "const_align_offset", issue = "90962")] | |||
| #[requires(!self.pointer.is_null())] | |||
| @@ -1785,6 +1824,7 @@ impl<T: ?Sized> From<&T> for NonNull<T> { | |||
| mod verify { | |||
| use super::*; | |||
| use crate::ptr::null_mut; | |||
| use crate::mem::align_of; | |||
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Towards #53
Changes
Three function contracts & four harnesses:
non_null::addnon_null::addrnon_null::align_offset, including both positive and negative harness that triggers panic. The ensures clause foralign_offsetis referenced fromalign_offsetinlibrary/core/src/ptr/mod.rs.Revalidation
To revalidate the verification results, run
kani verify-std -Z unstable-options "path/to/library" -Z function-contracts -Z mem-predicates --harness ptr::non_null::verify. This will run all six harnesses in the module. All default checks should pass:❗ Warning
Running the above command with the default installed cargo kani will result in compilation error due to the latest merged from PR#91. Detailed errors are commented under that PR. This issue is waiting to be resolved.
TODO:
Layoutto create dynamically sized arrays in place of fixed size array in harnesses. This approach currently has errors and is documented in discussion.requiresclause in contract to constraincountto be within object memory size: there is a current issue with usingub_checks::can_writeto get the object size. A workaround is implemented in the harness.By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.