zeroize: fix fallback code used by optimization_barrier (#1551)

The previous fallback code may potentially read uninitialized memory as `u8`.

Author: newpavlov

zeroize/CHANGELOG.md

@@ -7,8 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## 1.9.1 (UNRELEASED)
 ### Fixed
 - False positive failures in proxy allocator test ([#1538])
+- Potential uninitialized memory read in fallback code used by `optimization_barrier` ([#1551])
 
 [#1538]: https://github.com/RustCrypto/utils/pull/1538
+[#1551]: https://github.com/RustCrypto/utils/pull/1551
 
 ## 1.9.0 (2026-06-12)
 ### Added

zeroize/src/barrier.rs

@@ -91,7 +91,9 @@ pub fn optimization_barrier<T: ?Sized>(val: &T) {
         /// `#[inline(never)]` and `read_volatile`.
         #[inline(never)]
         fn custom_black_box(p: *const u8) {
-            let _ = unsafe { core::ptr::read_volatile(p) };
+            use core::mem::MaybeUninit;
+
+            let _: MaybeUninit<u8> = unsafe { core::ptr::read_volatile(p.cast()) };
         }
 
         core::hint::black_box(val);