1 files changed, 90 insertions, 0 deletions
diff --git a/getrandom/src/rdrand.rs b/getrandom/src/rdrand.rs
new file mode 100644
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+++ b/getrandom/src/rdrand.rs
@@ -0,0 +1,90 @@
+// Copyright 2018 Developers of the Rand project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Implementation for SGX using RDRAND instruction
+use crate::error::{FAILED_RDRAND, NO_RDRAND};
+#[cfg(not(target_feature = "rdrand"))]
+use crate::util::LazyBool;
+use crate::Error;
+use core::arch::x86_64::_rdrand64_step;
+use core::mem;
+
+// Recommendation from "Intel® Digital Random Number Generator (DRNG) Software
+// Implementation Guide" - Section 5.2.1 and "Intel® 64 and IA-32 Architectures
+// Software Developer’s Manual" - Volume 1 - Section 7.3.17.1.
+const RETRY_LIMIT: usize = 10;
+const WORD_SIZE: usize = mem::size_of::<u64>();
+
+#[target_feature(enable = "rdrand")]
+unsafe fn rdrand() -> Result<[u8; WORD_SIZE], Error> {
+    for _ in 0..RETRY_LIMIT {
+        let mut el = mem::zeroed();
+        if _rdrand64_step(&mut el) == 1 {
+            // AMD CPUs from families 14h to 16h (pre Ryzen) sometimes fail to
+            // set CF on bogus random data, so we check these values explicitly.
+            // See https://github.com/systemd/systemd/issues/11810#issuecomment-489727505
+            // We perform this check regardless of target to guard against
+            // any implementation that incorrectly fails to set CF.
+            if el != 0 && el != !0 {
+                return Ok(el.to_ne_bytes());
+            }
+            error!("RDRAND returned {:X}, CPU RNG may be broken", el);
+            // Keep looping in case this was a false positive.
+        }
+    }
+    Err(FAILED_RDRAND)
+}
+
+// "rdrand" target feature requires "+rdrnd" flag, see https://github.com/rust-lang/rust/issues/49653.
+#[cfg(all(target_env = "sgx", not(target_feature = "rdrand")))]
+compile_error!(
+    "SGX targets require 'rdrand' target feature. Enable by using -C target-feature=+rdrnd."
+);
+
+#[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(target_feature = "rdrand"))]
+fn is_rdrand_supported() -> bool {
+    use core::arch::x86_64::__cpuid;
+    // SAFETY: All x86_64 CPUs support CPUID leaf 1
+    const FLAG: u32 = 1 << 30;
+    static HAS_RDRAND: LazyBool = LazyBool::new();
+    HAS_RDRAND.unsync_init(|| unsafe { (__cpuid(1).ecx & FLAG) != 0 })
+}
+
+pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
+    if !is_rdrand_supported() {
+        return Err(NO_RDRAND);
+    }
+
+    // SAFETY: After this point, rdrand is supported, so calling the rdrand
+    // functions is not undefined behavior.
+    unsafe { rdrand_exact(dest) }
+}
+
+#[target_feature(enable = "rdrand")]
+unsafe fn rdrand_exact(dest: &mut [u8]) -> Result<(), Error> {
+    // We use chunks_exact_mut instead of chunks_mut as it allows almost all
+    // calls to memcpy to be elided by the compiler.
+    let mut chunks = dest.chunks_exact_mut(WORD_SIZE);
+    for chunk in chunks.by_ref() {
+        chunk.copy_from_slice(&rdrand()?);
+    }
+
+    let tail = chunks.into_remainder();
+    let n = tail.len();
+    if n > 0 {
+        tail.copy_from_slice(&rdrand()?[..n]);
+    }
+    Ok(())
+}