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udp: add WIP constant-time ConnectionID comparison

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This commit is contained in:
Joakim Frostegård 2022-04-15 02:27:13 +02:00
parent cad74df689
commit ce2723effa
1 changed files with 33 additions and 3 deletions
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36
aquatic_udp/src/common.rs
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@ -65,9 +65,10 @@ impl ConnectionValidator {
let valid_until = connection_id.0.to_ne_bytes()[..4].try_into().unwrap();
// Check that recreating ConnectionId with same inputs yields identical hash.
//
// I expect i64 comparison to be be constant-time.
if connection_id != self.create_connection_id_inner(valid_until, source_addr) {
if !Self::connection_id_eq_constant_time(
connection_id,
self.create_connection_id_inner(valid_until, source_addr),
) {
return false;
}
@ -97,6 +98,27 @@ impl ConnectionValidator {
ConnectionId(i64::from_ne_bytes(connection_id_bytes))
}
/// Compare ConnectionIDs in constant time
///
/// Use this instead of PartialEq::eq to avoid optimizations breaking constant
/// time HMAC comparison.
#[cfg(target_arch = "x86_64")]
fn connection_id_eq_constant_time(a: ConnectionId, b: ConnectionId) -> bool {
let mut eq = 0u8;
unsafe {
::std::arch::asm!(
"cmp {a}, {b}",
"sete {eq}",
a = in(reg) a.0,
b = in(reg) b.0,
eq = inout(reg_byte) eq,
);
}
eq != 0
}
}
#[derive(Debug)]
@ -368,4 +390,12 @@ mod tests {
quickcheck::TestResult::from_bool(original_valid)
}
}
#[quickcheck]
fn test_connection_id_eq(a: i64, b: i64) -> bool {
let a = ConnectionId(a);
let b = ConnectionId(b);
ConnectionValidator::connection_id_eq_constant_time(a, b) == (a == b)
}
}