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Fix and test correctness of constant_time_conditional_memxor on GCC #2734

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Fix and test correctness of constant_time_conditional_memxor on GCC #2734

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6b62327
Fix correctness of `constant_time_conditional_memxor` on GCC
ctz Oct 28, 2025
b9af09d
Adjust length of `constant_time_conditional_memxor` tests
ctz Oct 28, 2025
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6 changes: 3 additions & 3 deletions crypto/constant_time_test.c
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Original file line number Diff line number Diff line change
Expand Up @@ -103,8 +103,8 @@ void bssl_constant_time_test_conditional_memcpy(uint8_t dst[256], const uint8_t
}

// Exposes `constant_time_conditional_memxor` to Rust for tests only.
void bssl_constant_time_test_conditional_memxor(uint8_t dst[256],
const uint8_t src[256],
void bssl_constant_time_test_conditional_memxor(uint8_t dst[255],
const uint8_t src[255],
crypto_word_t b) {
constant_time_conditional_memxor(dst, src, 256, b);
constant_time_conditional_memxor(dst, src, 255, b);
}
1 change: 1 addition & 0 deletions crypto/internal.h
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Expand Up @@ -272,6 +272,7 @@ static inline void constant_time_conditional_memxor(void *dst, const void *src,
*(v32u8*)&out[i] ^= masks & *(v32u8 const*)&in[i];
}
out += n_vec;
in += n_vec;
n -= n_vec;
#endif
for (size_t i = 0; i < n; i++) {
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6 changes: 3 additions & 3 deletions src/tests/bb_bytes_tests.rs
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Expand Up @@ -53,8 +53,8 @@ fn constant_time_conditional_memcpy() -> Result<(), error::Unspecified> {
fn constant_time_conditional_memxor() -> Result<(), error::Unspecified> {
let rng = rand::SystemRandom::new();
for _ in 0..256 {
let mut out = rand::generate::<[u8; 256]>(&rng)?.expose();
let input = rand::generate::<[u8; 256]>(&rng)?.expose();
let mut out = rand::generate::<[u8; 255]>(&rng)?.expose();
let input = rand::generate::<[u8; 255]>(&rng)?.expose();

// Mask to 16 bits to make zero more likely than it would otherwise be.
let b = (rand::generate::<[u8; 1]>(&rng)?.expose()[0] & 0x0f) != 0;
Expand All @@ -66,7 +66,7 @@ fn constant_time_conditional_memxor() -> Result<(), error::Unspecified> {
};

prefixed_extern! {
fn bssl_constant_time_test_conditional_memxor(dst: &mut [u8; 256], src: &[u8; 256], b: BoolMask);
fn bssl_constant_time_test_conditional_memxor(dst: &mut [u8; 255], src: &[u8; 255], b: BoolMask);
}
unsafe {
bssl_constant_time_test_conditional_memxor(
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6 changes: 3 additions & 3 deletions src/tests/c_constant_time_tests.rs
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Expand Up @@ -65,8 +65,8 @@ fn constant_time_conditional_memcpy() -> Result<(), error::Unspecified> {
fn constant_time_conditional_memxor() -> Result<(), error::Unspecified> {
let rng = rand::SystemRandom::new();
for _ in 0..256 {
let mut out = rand::generate::<[u8; 256]>(&rng)?.expose();
let input = rand::generate::<[u8; 256]>(&rng)?.expose();
let mut out = rand::generate::<[u8; 255]>(&rng)?.expose();
let input = rand::generate::<[u8; 255]>(&rng)?.expose();

// Mask to 16 bits to make zero more likely than it would otherwise be.
let b = (rand::generate::<[u8; 1]>(&rng)?.expose()[0] & 0x0f) != 0;
Expand All @@ -78,7 +78,7 @@ fn constant_time_conditional_memxor() -> Result<(), error::Unspecified> {
};

prefixed_extern! {
fn bssl_constant_time_test_conditional_memxor(dst: &mut [u8; 256], src: &[u8; 256], b: BoolMask);
fn bssl_constant_time_test_conditional_memxor(dst: &mut [u8; 255], src: &[u8; 255], b: BoolMask);
}
unsafe {
bssl_constant_time_test_conditional_memxor(
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