Rollup merge of #129201 - joboet:random_faster_sources, r=joshtriplett

std: implement the `random` feature (alternative version)

Implements the ACP rust-lang/libs-team#393.

This PR is an alternative version of #129120 that replaces `getentropy` with `CCRandomGenerateBytes` (on macOS) and `arc4random_buf` (other BSDs), since that function is not suited for generating large amounts of data and should only be used to seed other CPRNGs. `CCRandomGenerateBytes`/`arc4random_buf` on the other hand is (on modern platforms) just as secure and uses its own, very strong CPRNG (ChaCha20 on the BSDs, AES on macOS) periodically seeded with `getentropy`.

Author: workingjubilee

src/shims/unix/macos/foreign_items.rs

@@ -78,6 +78,16 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 this.write_pointer(environ, dest)?;
             }
 
+            // Random data generation
+            "CCRandomGenerateBytes" => {
+                let [bytes, count] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
+                let bytes = this.read_pointer(bytes)?;
+                let count = this.read_target_usize(count)?;
+                let success = this.eval_libc_i32("kCCSuccess");
+                this.gen_random(bytes, count)?;
+                this.write_int(success, dest)?;
+            }
+
             // Time related shims
             "mach_absolute_time" => {
                 let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;

tests/pass-dep/libc/ccrandomgeneratebytes_apple.rs

@@ -0,0 +1,7 @@
+//@only-target: apple # This directly tests apple-only functions
+
+fn main() {
+    let mut bytes = [0u8; 24];
+    let ret = unsafe { libc::CCRandomGenerateBytes(bytes.as_mut_ptr().cast(), bytes.len()) };
+    assert_eq!(ret, libc::kCCSuccess);
+}