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// 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(())
}
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