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Check for AMD RDRAND bug #43

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Merged
merged 2 commits into from
Jun 29, 2019
Merged

Check for AMD RDRAND bug #43

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7c263d4
Check for AMD RDRAND bug
josephlr Jun 28, 2019
4c9817a
Don't do this check on SGX
josephlr Jun 29, 2019
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11 changes: 9 additions & 2 deletions src/rdrand.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,13 @@ unsafe fn rdrand() -> Result<[u8; WORD_SIZE], Error> {
for _ in 0..RETRY_LIMIT {
let mut el = mem::uninitialized();
if _rdrand64_step(&mut el) == 1 {
// AMD CPUs from families 14h to 16h (pre Ryzen) will sometimes give
// bogus random data. Discard these values and warn the user.
// See https://github.com/systemd/systemd/issues/11810#issuecomment-489727505
if el == 0 || el == !0 {
error!("RDRAND returned suspicious value {}, CPU RNG is broken", el);
return Err(Error::UNKNOWN)
}
return Ok(el.to_ne_bytes());
}
}
Expand All @@ -36,14 +43,14 @@ compile_error!(
"SGX targets require 'rdrand' target feature. Enable by using -C target-feature=+rdrnd."
);

#[cfg(any(target_env = "sgx", target_feature = "rdrand"))]
#[cfg(target_feature = "rdrand")]
fn is_rdrand_supported() -> bool {
true
}

// TODO use is_x86_feature_detected!("rdrand") when that works in core. See:
// https://github.com/rust-lang-nursery/stdsimd/issues/464
#[cfg(not(any(target_env = "sgx", target_feature = "rdrand")))]
#[cfg(not(target_feature = "rdrand"))]
fn is_rdrand_supported() -> bool {
use core::arch::x86_64::__cpuid;
use lazy_static::lazy_static;
Expand Down