]>
Commit | Line | Data |
---|---|---|
f20569fa XL |
1 | // Copyright 2018 Developers of the Rand project. |
2 | // | |
3 | // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | |
4 | // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license | |
5 | // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your | |
6 | // option. This file may not be copied, modified, or distributed | |
7 | // except according to those terms. | |
8 | ||
9 | //! Implementation for SGX using RDRAND instruction | |
10 | use crate::Error; | |
11 | use core::mem; | |
12 | ||
13 | cfg_if! { | |
14 | if #[cfg(target_arch = "x86_64")] { | |
15 | use core::arch::x86_64 as arch; | |
16 | use arch::_rdrand64_step as rdrand_step; | |
17 | } else if #[cfg(target_arch = "x86")] { | |
18 | use core::arch::x86 as arch; | |
19 | use arch::_rdrand32_step as rdrand_step; | |
20 | } | |
21 | } | |
22 | ||
23 | // Recommendation from "Intel® Digital Random Number Generator (DRNG) Software | |
24 | // Implementation Guide" - Section 5.2.1 and "Intel® 64 and IA-32 Architectures | |
25 | // Software Developer’s Manual" - Volume 1 - Section 7.3.17.1. | |
26 | const RETRY_LIMIT: usize = 10; | |
27 | const WORD_SIZE: usize = mem::size_of::<usize>(); | |
28 | ||
29 | #[target_feature(enable = "rdrand")] | |
30 | unsafe fn rdrand() -> Result<[u8; WORD_SIZE], Error> { | |
31 | for _ in 0..RETRY_LIMIT { | |
32 | let mut el = mem::zeroed(); | |
33 | if rdrand_step(&mut el) == 1 { | |
34 | // AMD CPUs from families 14h to 16h (pre Ryzen) sometimes fail to | |
35 | // set CF on bogus random data, so we check these values explicitly. | |
36 | // See https://github.com/systemd/systemd/issues/11810#issuecomment-489727505 | |
37 | // We perform this check regardless of target to guard against | |
38 | // any implementation that incorrectly fails to set CF. | |
39 | if el != 0 && el != !0 { | |
40 | return Ok(el.to_ne_bytes()); | |
41 | } | |
42 | // Keep looping in case this was a false positive. | |
43 | } | |
44 | } | |
45 | Err(Error::FAILED_RDRAND) | |
46 | } | |
47 | ||
48 | // "rdrand" target feature requires "+rdrnd" flag, see https://github.com/rust-lang/rust/issues/49653. | |
49 | #[cfg(all(target_env = "sgx", not(target_feature = "rdrand")))] | |
50 | compile_error!( | |
51 | "SGX targets require 'rdrand' target feature. Enable by using -C target-feature=+rdrnd." | |
52 | ); | |
53 | ||
54 | #[cfg(target_feature = "rdrand")] | |
55 | fn is_rdrand_supported() -> bool { | |
56 | true | |
57 | } | |
58 | ||
59 | // TODO use is_x86_feature_detected!("rdrand") when that works in core. See: | |
60 | // https://github.com/rust-lang-nursery/stdsimd/issues/464 | |
61 | #[cfg(not(target_feature = "rdrand"))] | |
62 | fn is_rdrand_supported() -> bool { | |
63 | use crate::util::LazyBool; | |
64 | ||
65 | // SAFETY: All Rust x86 targets are new enough to have CPUID, and if CPUID | |
66 | // is supported, CPUID leaf 1 is always supported. | |
67 | const FLAG: u32 = 1 << 30; | |
68 | static HAS_RDRAND: LazyBool = LazyBool::new(); | |
69 | HAS_RDRAND.unsync_init(|| unsafe { (arch::__cpuid(1).ecx & FLAG) != 0 }) | |
70 | } | |
71 | ||
72 | pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> { | |
73 | if !is_rdrand_supported() { | |
74 | return Err(Error::NO_RDRAND); | |
75 | } | |
76 | ||
77 | // SAFETY: After this point, rdrand is supported, so calling the rdrand | |
78 | // functions is not undefined behavior. | |
79 | unsafe { rdrand_exact(dest) } | |
80 | } | |
81 | ||
82 | #[target_feature(enable = "rdrand")] | |
83 | unsafe fn rdrand_exact(dest: &mut [u8]) -> Result<(), Error> { | |
84 | // We use chunks_exact_mut instead of chunks_mut as it allows almost all | |
85 | // calls to memcpy to be elided by the compiler. | |
86 | let mut chunks = dest.chunks_exact_mut(WORD_SIZE); | |
87 | for chunk in chunks.by_ref() { | |
88 | chunk.copy_from_slice(&rdrand()?); | |
89 | } | |
90 | ||
91 | let tail = chunks.into_remainder(); | |
92 | let n = tail.len(); | |
93 | if n > 0 { | |
94 | tail.copy_from_slice(&rdrand()?[..n]); | |
95 | } | |
96 | Ok(()) | |
97 | } |