Use constant_time_eq instead of our bespoke implementation

common/Cargo.toml

@@ -34,7 +34,6 @@ unicode_names2 = { workspace = true }
 lock_api = "0.4"
 radium = "1.1"
 siphasher = "1"
-volatile = "0.3"
 
 [target.'cfg(windows)'.dependencies]
 widestring = { workspace = true }

common/src/cmp.rs

@@ -1,48 +0,0 @@
-use volatile::Volatile;
-
-/// Compare 2 byte slices in a way that ensures that the timing of the operation can't be used to
-/// glean any information about the data.
-#[inline(never)]
-#[cold]
-pub fn timing_safe_cmp(a: &[u8], b: &[u8]) -> bool {
-    // we use raw pointers here to keep faithful to the C implementation and
-    // to try to avoid any optimizations rustc might do with slices
-    let len_a = a.len();
-    let a = a.as_ptr();
-    let len_b = b.len();
-    let b = b.as_ptr();
-    /* The volatile type declarations make sure that the compiler has no
-     * chance to optimize and fold the code in any way that may change
-     * the timing.
-     */
-    let mut result: u8 = 0;
-    /* loop count depends on length of b */
-    let length: Volatile<usize> = Volatile::new(len_b);
-    let mut left: Volatile<*const u8> = Volatile::new(std::ptr::null());
-    let mut right: Volatile<*const u8> = Volatile::new(b);
-
-    /* don't use else here to keep the amount of CPU instructions constant,
-     * volatile forces re-evaluation
-     *  */
-    if len_a == length.read() {
-        left.write(Volatile::new(a).read());
-        result = 0;
-    }
-    if len_a != length.read() {
-        left.write(b);
-        result = 1;
-    }
-
-    for _ in 0..length.read() {
-        let l = left.read();
-        left.write(l.wrapping_add(1));
-        let r = right.read();
-        right.write(r.wrapping_add(1));
-        // safety: the 0..length range will always be either:
-        // * as long as the length of both a and b, if len_a and len_b are equal
-        // * as long as b, and both `left` and `right` are b
-        result |= unsafe { l.read_volatile() ^ r.read_volatile() };
-    }
-
-    result == 0
-}

common/src/lib.rs

@@ -10,7 +10,6 @@ pub mod atomic;
 pub mod borrow;
 pub mod boxvec;
 pub mod cformat;
-pub mod cmp;
 #[cfg(any(unix, windows, target_os = "wasi"))]
 pub mod crt_fd;
 pub mod encodings;