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Rust Sanitizers and Miri
Purpose
Guide agents through runtime safety validation for Rust: ASan/TSan/MSan/UBSan via RUSTFLAGS, Miri for compile-time UB detection in unsafe code, and interpreting sanitizer reports.
Triggers
- "How do I run AddressSanitizer on Rust code?"
- "How do I use Miri to check my unsafe Rust?"
- "How do I run ThreadSanitizer on a Rust program?"
- "My unsafe Rust might have UB — how do I detect it?"
- "How do I interpret a Rust ASan report?"
- "Can I run Rust sanitizers on stable?"
Workflow
1. Sanitizers in Rust (nightly required)
Rust sanitizers require nightly and a compatible platform:
bash
# Install nightly
rustup toolchain install nightly
rustup component add rust-src --toolchain nightly
# AddressSanitizer (Linux, macOS)
RUSTFLAGS="-Z sanitizer=address" \
cargo +nightly test -Zbuild-std \
--target x86_64-unknown-linux-gnu
# ThreadSanitizer (Linux)
RUSTFLAGS="-Z sanitizer=thread" \
cargo +nightly test -Zbuild-std \
--target x86_64-unknown-linux-gnu
# MemorySanitizer (Linux, requires all-instrumented build)
RUSTFLAGS="-Z sanitizer=memory -Zsanitizer-memory-track-origins" \
cargo +nightly test -Zbuild-std \
--target x86_64-unknown-linux-gnu
# UndefinedBehaviorSanitizer
RUSTFLAGS="-Z sanitizer=undefined" \
cargo +nightly test -Zbuild-std \
--target x86_64-unknown-linux-gnu-Zbuild-std rebuilds the standard library with the sanitizer, which is necessary for accurate results.
2. Stable sanitizer workaround
For stable Rust, use the cross tool with a Docker image that has sanitizers pre-configured, or run cargo test inside a Docker container with a nightly image.
Alternatively, for simpler UB checking without nightly:
bash
# cargo-sanitize (wrapper)
cargo install cargo-sanitize
cargo sanitize address3. Interpreting ASan output in Rust
==12345==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000000050
READ of size 4 at 0x602000000050 thread T0
#0 0x401234 in myapp::module::function /src/main.rs:15
#1 0x401567 in myapp::main /src/main.rs:42
0x602000000050 is located 0 bytes after a 40-byte region allocated at:
#0 0x... in alloc::alloc::alloc ...
#1 0x... in myapp::create_buffer /src/main.rs:10Rust-specific patterns:
| ASan error | Likely Rust cause |
|---|---|
heap-buffer-overflow | unsafe slice access past bounds |
use-after-free | unsafe pointer use after Vec realloc |
stack-use-after-return | Returning reference to local |
heap-use-after-free | Use after drop() or Box::from_raw |
4. Miri — interpreter for undefined behaviour
Miri interprets Rust MIR and detects UB that sanitizers might miss:
bash
# Install Miri (requires nightly)
rustup +nightly component add miri
# Run tests under Miri
cargo +nightly miri test
# Run specific test
cargo +nightly miri test test_name
# Run a binary under Miri
cargo +nightly miri run
# Run with Stacked Borrows model (strict aliasing)
MIRIFLAGS="-Zmiri-strict-provenance" cargo +nightly miri test
# Disable isolation (allow file I/O, randomness)
MIRIFLAGS="-Zmiri-disable-isolation" cargo +nightly miri test5. What Miri detects
rust
// 1. Dangling pointer use
unsafe {
let x = Box::new(42);
let ptr = Box::into_raw(x);
let _ = Box::from_raw(ptr); // drop
let _val = *ptr; // Miri: use of dangling pointer
}
// 2. Invalid enum discriminant
let x: u8 = 3;
let e = unsafe { std::mem::transmute::<u8, MyEnum>(x) };
// Miri: enum value has invalid tag
// 3. Uninitialized memory read
let uninit: MaybeUninit<u32> = MaybeUninit::uninit();
let val = unsafe { uninit.assume_init() }; // Miri: reading uninitialized bytes
// 4. Stacked borrows violation
let mut x = 5u32;
let ptr = &mut x as *mut u32;
let _ref = &x; // shared reference
unsafe { *ptr = 10; } // Miri: mutable access while shared borrow exists
// 5. Data races (with threads)
// Miri simulates sequential execution and detects races via Stacked Borrows6. ThreadSanitizer for Rust
bash
RUSTFLAGS="-Z sanitizer=thread" \
RUST_TEST_THREADS=8 \
cargo +nightly test -Zbuild-std \
--target x86_64-unknown-linux-gnu 2>&1 | head -50TSan output:
WARNING: ThreadSanitizer: data race (pid=12345)
Write of size 4 at 0x7f... by thread T2 (mutexes: write M1):
#0 myapp::counter::increment src/counter.rs:10
Previous read of size 4 at 0x7f... by thread T1:
#0 myapp::counter::get src/counter.rs:57. Miri configuration via MIRIFLAGS
| Flag | Effect |
|---|---|
-Zmiri-disable-isolation | Allow I/O, clock, randomness |
-Zmiri-strict-provenance | Strict pointer provenance (stricter than LLVM) |
-Zmiri-symbolic-alignment-check | Stricter alignment checking |
-Zmiri-check-number-validity | Check float/int validity |
-Zmiri-num-cpus=N | Simulate N CPUs (for concurrency) |
-Zmiri-seed=N | Seed for random scheduling |
-Zmiri-ignore-leaks | Suppress memory leak errors |
-Zmiri-tag-raw-pointers | Track raw pointer provenance |
8. CI integration
yaml
# GitHub Actions
- name: Miri
run: |
rustup toolchain install nightly
rustup +nightly component add miri
cargo +nightly miri test
env:
MIRIFLAGS: "-Zmiri-disable-isolation"
- name: ASan (nightly)
run: |
rustup component add rust-src --toolchain nightly
RUSTFLAGS="-Z sanitizer=address" \
cargo +nightly test -Zbuild-std \
--target x86_64-unknown-linux-gnuRelated skills
- Use
skills/rust/rust-debuggingfor GDB/LLDB debugging of Rust panics - Use
skills/runtimes/sanitizersfor C/C++ sanitizer usage and comparison - Use
skills/rust/rust-unsafefor unsafe Rust patterns and review checklist - Use
skills/runtimes/fuzzingto generate inputs that trigger sanitizer errors
