264 lines
13 KiB
Rust
264 lines
13 KiB
Rust
// Copyright 2019 Developers of the Rand project.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Interface to the operating system's random number generator.
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//!
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//! # Supported targets
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//!
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//! | Target | Target Triple | Implementation
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//! | ----------------- | ------------------ | --------------
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//! | Linux, Android | `*‑linux‑*` | [`getrandom`][1] system call if available, otherwise [`/dev/urandom`][2] after successfully polling `/dev/random`
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//! | Windows | `*‑windows‑*` | [`BCryptGenRandom`]
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//! | macOS | `*‑apple‑darwin` | [`getentropy`][3] if available, otherwise [`/dev/random`][4] (identical to `/dev/urandom`)
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//! | iOS | `*‑apple‑ios` | [`SecRandomCopyBytes`]
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//! | FreeBSD | `*‑freebsd` | [`getrandom`][5] if available, otherwise [`kern.arandom`][6]
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//! | OpenBSD | `*‑openbsd` | [`getentropy`][7]
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//! | NetBSD | `*‑netbsd` | [`kern.arandom`][8]
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//! | Dragonfly BSD | `*‑dragonfly` | [`getrandom`][9] if available, otherwise [`/dev/random`][10]
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//! | Solaris, illumos | `*‑solaris`, `*‑illumos` | [`getrandom`][11] if available, otherwise [`/dev/random`][12]
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//! | Fuchsia OS | `*‑fuchsia` | [`cprng_draw`]
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//! | Redox | `*‑redox` | `/dev/urandom`
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//! | Haiku | `*‑haiku` | `/dev/random` (identical to `/dev/urandom`)
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//! | Hermit | `x86_64-*-hermit` | [`RDRAND`]
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//! | SGX | `x86_64‑*‑sgx` | [`RDRAND`]
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//! | VxWorks | `*‑wrs‑vxworks‑*` | `randABytes` after checking entropy pool initialization with `randSecure`
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//! | ESP-IDF | `*‑espidf` | [`esp_fill_random`]
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//! | Emscripten | `*‑emscripten` | `/dev/random` (identical to `/dev/urandom`)
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//! | WASI | `wasm32‑wasi` | [`random_get`]
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//! | Web Browser | `wasm32‑*‑unknown` | [`Crypto.getRandomValues`], see [WebAssembly support]
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//! | Node.js | `wasm32‑*‑unknown` | [`crypto.randomBytes`], see [WebAssembly support]
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//! | SOLID | `*-kmc-solid_*` | `SOLID_RNG_SampleRandomBytes`
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//! | Nintendo 3DS | `armv6k-nintendo-3ds` | [`getrandom`][1]
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//!
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//! There is no blanket implementation on `unix` targets that reads from
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//! `/dev/urandom`. This ensures all supported targets are using the recommended
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//! interface and respect maximum buffer sizes.
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//!
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//! Pull Requests that add support for new targets to `getrandom` are always welcome.
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//!
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//! ## Unsupported targets
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//!
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//! By default, `getrandom` will not compile on unsupported targets, but certain
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//! features allow a user to select a "fallback" implementation if no supported
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//! implementation exists.
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//!
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//! All of the below mechanisms only affect unsupported
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//! targets. Supported targets will _always_ use their supported implementations.
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//! This prevents a crate from overriding a secure source of randomness
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//! (either accidentally or intentionally).
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//!
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//! ### RDRAND on x86
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//!
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//! *If the `rdrand` Cargo feature is enabled*, `getrandom` will fallback to using
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//! the [`RDRAND`] instruction to get randomness on `no_std` `x86`/`x86_64`
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//! targets. This feature has no effect on other CPU architectures.
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//!
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//! ### WebAssembly support
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//!
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//! This crate fully supports the
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//! [`wasm32-wasi`](https://github.com/CraneStation/wasi) and
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//! [`wasm32-unknown-emscripten`](https://www.hellorust.com/setup/emscripten/)
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//! targets. However, the `wasm32-unknown-unknown` target (i.e. the target used
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//! by `wasm-pack`) is not automatically
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//! supported since, from the target name alone, we cannot deduce which
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//! JavaScript interface is in use (or if JavaScript is available at all).
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//!
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//! Instead, *if the `js` Cargo feature is enabled*, this crate will assume
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//! that you are building for an environment containing JavaScript, and will
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//! call the appropriate methods. Both web browser (main window and Web Workers)
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//! and Node.js environments are supported, invoking the methods
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//! [described above](#supported-targets) using the
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//! [wasm-bindgen](https://github.com/rust-lang/rust-bindgen) toolchain.
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//!
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//! This feature has no effect on targets other than `wasm32-unknown-unknown`.
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//!
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//! ### Custom implementations
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//!
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//! The [`register_custom_getrandom!`] macro allows a user to mark their own
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//! function as the backing implementation for [`getrandom`]. See the macro's
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//! documentation for more information about writing and registering your own
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//! custom implementations.
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//!
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//! Note that registering a custom implementation only has an effect on targets
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//! that would otherwise not compile. Any supported targets (including those
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//! using `rdrand` and `js` Cargo features) continue using their normal
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//! implementations even if a function is registered.
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//!
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//! ### Indirect Dependencies
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//!
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//! If `getrandom` is not a direct dependency of your crate, you can still
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//! enable any of the above fallback behaviors by enabling the relevant
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//! feature in your root crate's `Cargo.toml`:
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//! ```toml
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//! [dependencies]
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//! getrandom = { version = "0.2", features = ["js"] }
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//! ```
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//!
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//! ## Early boot
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//!
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//! Sometimes, early in the boot process, the OS has not collected enough
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//! entropy to securely seed its RNG. This is especially common on virtual
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//! machines, where standard "random" events are hard to come by.
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//!
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//! Some operating system interfaces always block until the RNG is securely
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//! seeded. This can take anywhere from a few seconds to more than a minute.
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//! A few (Linux, NetBSD and Solaris) offer a choice between blocking and
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//! getting an error; in these cases, we always choose to block.
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//!
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//! On Linux (when the `getrandom` system call is not available), reading from
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//! `/dev/urandom` never blocks, even when the OS hasn't collected enough
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//! entropy yet. To avoid returning low-entropy bytes, we first poll
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//! `/dev/random` and only switch to `/dev/urandom` once this has succeeded.
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//!
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//! ## Error handling
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//!
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//! We always choose failure over returning insecure "random" bytes. In general,
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//! on supported platforms, failure is highly unlikely, though not impossible.
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//! If an error does occur, then it is likely that it will occur on every call to
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//! `getrandom`, hence after the first successful call one can be reasonably
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//! confident that no errors will occur.
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//!
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//! [1]: http://man7.org/linux/man-pages/man2/getrandom.2.html
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//! [2]: http://man7.org/linux/man-pages/man4/urandom.4.html
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//! [3]: https://www.unix.com/man-page/mojave/2/getentropy/
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//! [4]: https://www.unix.com/man-page/mojave/4/random/
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//! [5]: https://www.freebsd.org/cgi/man.cgi?query=getrandom&manpath=FreeBSD+12.0-stable
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//! [6]: https://www.freebsd.org/cgi/man.cgi?query=random&sektion=4
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//! [7]: https://man.openbsd.org/getentropy.2
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//! [8]: https://man.netbsd.org/sysctl.7
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//! [9]: https://leaf.dragonflybsd.org/cgi/web-man?command=getrandom
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//! [10]: https://leaf.dragonflybsd.org/cgi/web-man?command=random§ion=4
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//! [11]: https://docs.oracle.com/cd/E88353_01/html/E37841/getrandom-2.html
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//! [12]: https://docs.oracle.com/cd/E86824_01/html/E54777/random-7d.html
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//!
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//! [`BCryptGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
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//! [`Crypto.getRandomValues`]: https://www.w3.org/TR/WebCryptoAPI/#Crypto-method-getRandomValues
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//! [`RDRAND`]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide
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//! [`SecRandomCopyBytes`]: https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc
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//! [`cprng_draw`]: https://fuchsia.dev/fuchsia-src/zircon/syscalls/cprng_draw
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//! [`crypto.randomBytes`]: https://nodejs.org/api/crypto.html#crypto_crypto_randombytes_size_callback
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//! [`esp_fill_random`]: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/random.html#_CPPv415esp_fill_randomPv6size_t
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//! [`random_get`]: https://github.com/WebAssembly/WASI/blob/main/phases/snapshot/docs.md#-random_getbuf-pointeru8-buf_len-size---errno
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//! [WebAssembly support]: #webassembly-support
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#![doc(
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html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
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html_favicon_url = "https://www.rust-lang.org/favicon.ico",
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html_root_url = "https://docs.rs/getrandom/0.2.7"
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)]
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#![no_std]
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#![warn(rust_2018_idioms, unused_lifetimes, missing_docs)]
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#![cfg_attr(docsrs, feature(doc_cfg))]
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#[macro_use]
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extern crate cfg_if;
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mod error;
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mod util;
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// To prevent a breaking change when targets are added, we always export the
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// register_custom_getrandom macro, so old Custom RNG crates continue to build.
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#[cfg(feature = "custom")]
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mod custom;
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#[cfg(feature = "std")]
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mod error_impls;
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pub use crate::error::Error;
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// System-specific implementations.
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//
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// These should all provide getrandom_inner with the same signature as getrandom.
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cfg_if! {
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if #[cfg(any(target_os = "emscripten", target_os = "haiku",
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target_os = "redox"))] {
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mod util_libc;
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#[path = "use_file.rs"] mod imp;
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} else if #[cfg(any(target_os = "android", target_os = "linux"))] {
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mod util_libc;
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mod use_file;
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#[path = "linux_android.rs"] mod imp;
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} else if #[cfg(any(target_os = "illumos", target_os = "solaris"))] {
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mod util_libc;
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mod use_file;
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#[path = "solaris_illumos.rs"] mod imp;
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} else if #[cfg(any(target_os = "freebsd", target_os = "netbsd"))] {
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mod util_libc;
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#[path = "bsd_arandom.rs"] mod imp;
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} else if #[cfg(target_os = "dragonfly")] {
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mod util_libc;
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mod use_file;
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#[path = "dragonfly.rs"] mod imp;
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} else if #[cfg(target_os = "fuchsia")] {
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#[path = "fuchsia.rs"] mod imp;
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} else if #[cfg(target_os = "ios")] {
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#[path = "ios.rs"] mod imp;
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} else if #[cfg(target_os = "macos")] {
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mod util_libc;
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mod use_file;
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#[path = "macos.rs"] mod imp;
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} else if #[cfg(target_os = "openbsd")] {
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mod util_libc;
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#[path = "openbsd.rs"] mod imp;
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} else if #[cfg(target_os = "wasi")] {
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#[path = "wasi.rs"] mod imp;
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} else if #[cfg(all(target_arch = "x86_64", target_os = "hermit"))] {
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#[path = "rdrand.rs"] mod imp;
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} else if #[cfg(target_os = "vxworks")] {
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mod util_libc;
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#[path = "vxworks.rs"] mod imp;
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} else if #[cfg(target_os = "solid_asp3")] {
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#[path = "solid.rs"] mod imp;
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} else if #[cfg(target_os = "espidf")] {
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#[path = "espidf.rs"] mod imp;
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} else if #[cfg(windows)] {
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#[path = "windows.rs"] mod imp;
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} else if #[cfg(all(target_arch = "x86_64", target_env = "sgx"))] {
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#[path = "rdrand.rs"] mod imp;
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} else if #[cfg(all(feature = "rdrand",
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any(target_arch = "x86_64", target_arch = "x86")))] {
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#[path = "rdrand.rs"] mod imp;
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} else if #[cfg(all(feature = "js",
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target_arch = "wasm32", target_os = "unknown"))] {
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#[path = "js.rs"] mod imp;
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} else if #[cfg(all(target_os = "horizon", target_arch = "arm"))] {
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// We check for target_arch = "arm" because the Nintendo Switch also
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// uses Horizon OS (it is aarch64).
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mod util_libc;
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#[path = "3ds.rs"] mod imp;
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} else if #[cfg(feature = "custom")] {
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use custom as imp;
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} else if #[cfg(all(target_arch = "wasm32", target_os = "unknown"))] {
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compile_error!("the wasm32-unknown-unknown target is not supported by \
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default, you may need to enable the \"js\" feature. \
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For more information see: \
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https://docs.rs/getrandom/#webassembly-support");
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} else {
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compile_error!("target is not supported, for more information see: \
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https://docs.rs/getrandom/#unsupported-targets");
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}
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}
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/// Fill `dest` with random bytes from the system's preferred random number
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/// source.
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///
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/// This function returns an error on any failure, including partial reads. We
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/// make no guarantees regarding the contents of `dest` on error. If `dest` is
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/// empty, `getrandom` immediately returns success, making no calls to the
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/// underlying operating system.
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///
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/// Blocking is possible, at least during early boot; see module documentation.
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///
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/// In general, `getrandom` will be fast enough for interactive usage, though
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/// significantly slower than a user-space CSPRNG; for the latter consider
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/// [`rand::thread_rng`](https://docs.rs/rand/*/rand/fn.thread_rng.html).
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pub fn getrandom(dest: &mut [u8]) -> Result<(), Error> {
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if dest.is_empty() {
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return Ok(());
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}
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imp::getrandom_inner(dest)
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}
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