Raise minimum supported Apple OS versions (#388)

Author: BlackHoleFox

CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Changed
+- Raise minimum supported Apple OS versions to macOS 10.12 and iOS 10.
+
 ## [0.2.11] - 2023-11-08
 ### Added
 - GNU/Hurd support [#370]

src/apple-other.rs

@@ -1,24 +1,29 @@
-// Copyright 2018 Developers of the Rand project.
+// Copyright 2023 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 iOS
+//! Implementation for iOS, tvOS, and watchOS where `getentropy` is unavailable.
 use crate::Error;
-use core::{ffi::c_void, mem::MaybeUninit, ptr::null};
+use core::{ffi::c_void, mem::MaybeUninit};
 
-#[link(name = "Security", kind = "framework")]
+// libsystem contains the libc of Darwin, and every binary ends up linked against it either way. This
+// makes it a more lightweight choice compared to `Security.framework`.
 extern "C" {
-    fn SecRandomCopyBytes(rnd: *const c_void, count: usize, bytes: *mut u8) -> i32;
+    // This RNG uses a thread-local CSPRNG to provide data, which is seeded by the operating system's root CSPRNG.
+    // Its the best option after `getentropy` on modern Darwin-based platforms that also avoids the
+    // high startup costs and linking of Security.framework.
+    //
+    // While its just an implementation detail, `Security.framework` just calls into this anyway.
+    fn CCRandomGenerateBytes(bytes: *mut c_void, size: usize) -> i32;
 }
 
 pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
-    // Apple's documentation guarantees kSecRandomDefault is a synonym for NULL.
-    let ret = unsafe { SecRandomCopyBytes(null(), dest.len(), dest.as_mut_ptr() as *mut u8) };
-    // errSecSuccess (from SecBase.h) is always zero.
+    let ret = unsafe { CCRandomGenerateBytes(dest.as_mut_ptr() as *mut c_void, dest.len()) };
+    // kCCSuccess (from CommonCryptoError.h) is always zero.
     if ret != 0 {
         Err(Error::IOS_SEC_RANDOM)
     } else {

src/error.rs

@@ -37,7 +37,9 @@ impl Error {
     pub const ERRNO_NOT_POSITIVE: Error = internal_error(1);
     /// Encountered an unexpected situation which should not happen in practice.
     pub const UNEXPECTED: Error = internal_error(2);
-    /// Call to iOS [`SecRandomCopyBytes`](https://developer.apple.com/documentation/security/1399291-secrandomcopybytes) failed.
+    /// Call to [`CCRandomGenerateBytes`](https://opensource.apple.com/source/CommonCrypto/CommonCrypto-60074/include/CommonRandom.h.auto.html) failed
+    /// on iOS, tvOS, or waatchOS.
+    // TODO: Update this constant name in the next breaking release.
     pub const IOS_SEC_RANDOM: Error = internal_error(3);
     /// Call to Windows [`RtlGenRandom`](https://docs.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom) failed.
     pub const WINDOWS_RTL_GEN_RANDOM: Error = internal_error(4);

src/lib.rs

@@ -14,8 +14,8 @@
 //! | ----------------- | ------------------ | --------------
 //! | Linux, Android    | `*‑linux‑*`        | [`getrandom`][1] system call if available, otherwise [`/dev/urandom`][2] after successfully polling `/dev/random`
 //! | Windows           | `*‑windows‑*`      | [`BCryptGenRandom`]
-//! | macOS             | `*‑apple‑darwin`   | [`getentropy`][3] if available, otherwise [`/dev/urandom`][4] (identical to `/dev/random`)
-//! | iOS, tvOS, watchOS | `*‑apple‑ios`, `*-apple-tvos`, `*-apple-watchos` | [`SecRandomCopyBytes`]
+//! | macOS             | `*‑apple‑darwin`   | [`getentropy`][3]
+//! | iOS, tvOS, watchOS | `*‑apple‑ios`, `*-apple-tvos`, `*-apple-watchos` | [`CCRandomGenerateBytes`]
 //! | FreeBSD           | `*‑freebsd`        | [`getrandom`][5] if available, otherwise [`kern.arandom`][6]
 //! | OpenBSD           | `*‑openbsd`        | [`getentropy`][7]
 //! | NetBSD            | `*‑netbsd`         | [`getrandom`][16] if available, otherwise [`kern.arandom`][8]
@@ -179,7 +179,7 @@
 //! [`BCryptGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
 //! [`Crypto.getRandomValues`]: https://www.w3.org/TR/WebCryptoAPI/#Crypto-method-getRandomValues
 //! [`RDRAND`]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide
-//! [`SecRandomCopyBytes`]: https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc
+//! [`CCRandomGenerateBytes`]: https://opensource.apple.com/source/CommonCrypto/CommonCrypto-60074/include/CommonRandom.h.auto.html
 //! [`cprng_draw`]: https://fuchsia.dev/fuchsia-src/zircon/syscalls/cprng_draw
 //! [`crypto.randomFillSync`]: https://nodejs.org/api/crypto.html#cryptorandomfillsyncbuffer-offset-size
 //! [`esp_fill_random`]: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/random.html#_CPPv415esp_fill_randomPv6size_t
@@ -250,7 +250,6 @@ cfg_if! {
         #[path = "apple-other.rs"] mod imp;
     } else if #[cfg(target_os = "macos")] {
         mod util_libc;
-        mod use_file;
         #[path = "macos.rs"] mod imp;
     } else if #[cfg(target_os = "openbsd")] {
         mod util_libc;

src/macos.rs

@@ -1,4 +1,4 @@
-// Copyright 2019 Developers of the Rand project.
+// Copyright 2023 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
@@ -7,30 +7,20 @@
 // except according to those terms.
 
 //! Implementation for macOS
-use crate::{
-    use_file,
-    util_libc::{last_os_error, Weak},
-    Error,
-};
-use core::mem::{self, MaybeUninit};
+use crate::{util_libc::last_os_error, Error};
+use core::mem::MaybeUninit;
 
-type GetEntropyFn = unsafe extern "C" fn(*mut u8, libc::size_t) -> libc::c_int;
+extern "C" {
+    // Supported as of macOS 10.12+.
+    fn getentropy(buf: *mut u8, size: libc::size_t) -> libc::c_int;
+}
 
 pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
-    // getentropy(2) was added in 10.12, Rust supports 10.7+
-    static GETENTROPY: Weak = unsafe { Weak::new("getentropy\0") };
-    if let Some(fptr) = GETENTROPY.ptr() {
-        let func: GetEntropyFn = unsafe { mem::transmute(fptr) };
-        for chunk in dest.chunks_mut(256) {
-            let ret = unsafe { func(chunk.as_mut_ptr() as *mut u8, chunk.len()) };
-            if ret != 0 {
-                return Err(last_os_error());
-            }
+    for chunk in dest.chunks_mut(256) {
+        let ret = unsafe { getentropy(chunk.as_mut_ptr() as *mut u8, chunk.len()) };
+        if ret != 0 {
+            return Err(last_os_error());
         }
-        Ok(())
-    } else {
-        // We fallback to reading from /dev/random instead of SecRandomCopyBytes
-        // to avoid high startup costs and linking the Security framework.
-        use_file::getrandom_inner(dest)
     }
+    Ok(())
 }

src/use_file.rs

@@ -1,4 +1,4 @@
-// Copyright 2018 Developers of the Rand project.
+// Copyright 2023 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
@@ -20,7 +20,7 @@ use core::{
 // We prefer using /dev/urandom and only use /dev/random if the OS
 // documentation indicates that /dev/urandom is insecure.
 // On Solaris/Illumos, see src/solaris_illumos.rs
-// On Dragonfly, Haiku, macOS, and QNX Neutrino the devices are identical.
+// On Dragonfly, Haiku, and QNX Neutrino the devices are identical.
 #[cfg(any(target_os = "solaris", target_os = "illumos"))]
 const FILE_PATH: &str = "/dev/random\0";
 #[cfg(any(
@@ -30,7 +30,6 @@ const FILE_PATH: &str = "/dev/random\0";
     target_os = "redox",
     target_os = "dragonfly",
     target_os = "haiku",
-    target_os = "macos",
     target_os = "nto",
 ))]
 const FILE_PATH: &str = "/dev/urandom\0";