Add a minimal KUnit test that checks that KCSAN detects data races in Rust code: two threads concurrently increment a shared counter without synchronization, and a probe on the console tracepoint waits for the KCSAN report (similar to kcsan_test.c):
| BUG: KCSAN: data-race in _RNvNtNtCskctMpSfuwL9_6kernel10kcsan_test5tests8racy_inc / _RNvNtNtCskctMpSfuwL9_6kernel10kcsan_test5tests8racy_inc | | read-write to 0xffffffffb751ae28 of 8 bytes by task 116 on cpu 5: | _RNvNtNtCskctMpSfuwL9_6kernel10kcsan_test5tests8racy_inc+0x1c/0x30 | _RNvNtNtCskctMpSfuwL9_6kernel10kcsan_test5tests28kunit_rust_wrapper_data_race+0x28c/0x850 | kunit_try_run_case+0xdf/0x2a0 | kunit_generic_run_threadfn_adapter+0x48/0x80 | kthread+0x234/0x280 | ret_from_fork+0xf8/0x280 | ret_from_fork_asm+0x1a/0x30 | | read-write to 0xffffffffb751ae28 of 8 bytes by task 12 on cpu 3: | _RNvNtNtCskctMpSfuwL9_6kernel10kcsan_test5tests8racy_inc+0x1c/0x30 | _RNvXsb_NtCskctMpSfuwL9_6kernel9workqueueINtNtCs1G77UTwpz6o_4core3pin3PinINtNtNtB7_5alloc4kbox3BoxINtB5_11ClosureWorkNCNvNtNtB7_10kcsan_test5tests9data_races_0ENtNtB1d_9allocator7KmallocEEINtB5_15WorkItemPointerKy0_E3runB7_+0x55/0x120 | process_scheduled_works+0x4cd/0x970 | worker_thread+0x4de/0x6e0 | kthread+0x234/0x280 | ret_from_fork+0xf8/0x280 | ret_from_fork_asm+0x1a/0x30 | | value changed: 0x000000000000022b -> 0x00000000000005a2 | [...] The test is intentionally kept minimal; comprehensive tests of KCSAN's runtime behaviour are in kernel/kcsan/kcsan_test.c. Assisted-by: Antigravity Signed-off-by: Marco Elver <[email protected]> --- MAINTAINERS | 1 + rust/bindings/bindings_helper.h | 1 + rust/kernel/Kconfig.test | 11 +++ rust/kernel/kcsan_test.rs | 120 ++++++++++++++++++++++++++++++++ rust/kernel/lib.rs | 2 + 5 files changed, 135 insertions(+) create mode 100644 rust/kernel/kcsan_test.rs diff --git a/MAINTAINERS b/MAINTAINERS index cc3cae2e378b..3fbbfbb31f5d 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -14089,6 +14089,7 @@ F: Documentation/dev-tools/kcsan.rst F: include/linux/kcsan*.h F: kernel/kcsan/ F: lib/Kconfig.kcsan +F: rust/kernel/kcsan_test.rs F: scripts/Makefile.kcsan KDUMP diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index 4b31aa7f432f..b06d5142d6e1 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -97,6 +97,7 @@ #include <linux/xarray.h> #include <net/genetlink.h> #include <net/netlink.h> +#include <trace/events/printk.h> #include <trace/events/rust_sample.h> /* diff --git a/rust/kernel/Kconfig.test b/rust/kernel/Kconfig.test index e6a5c7a795f0..caf98a23de76 100644 --- a/rust/kernel/Kconfig.test +++ b/rust/kernel/Kconfig.test @@ -83,4 +83,15 @@ config RUST_BITFIELD_KUNIT_TEST If unsure, say N. +config RUST_KCSAN_KUNIT_TEST + bool "KUnit test for KCSAN instrumentation of Rust code" if !KUNIT_ALL_TESTS + depends on KCSAN && HAVE_KCSAN_RUSTC && TRACEPOINTS + default KUNIT_ALL_TESTS + help + This option enables a KUnit test checking that KCSAN detects data + races in Rust code. The test needs at least 2 CPUs to reliably + observe a data race. + + If unsure, say N. + endif diff --git a/rust/kernel/kcsan_test.rs b/rust/kernel/kcsan_test.rs new file mode 100644 index 000000000000..5ddc9090cd6e --- /dev/null +++ b/rust/kernel/kcsan_test.rs @@ -0,0 +1,120 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! KUnit test checking that KCSAN detects data races in Rust code. + +#[macros::kunit_tests(rust_kcsan)] +mod tests { + use crate::{ + bindings, + error::to_result, + ffi::{c_char, c_void}, + prelude::*, + sync::{ + atomic::{Atomic, Relaxed}, + Arc, Completion, + }, + time::{Delta, Instant, Monotonic}, + types::ScopeGuard, + workqueue, + }; + use core::{cell::UnsafeCell, ptr, slice}; + + struct Racy(UnsafeCell<u64>); + + // SAFETY: Not actually safe: unsynchronized concurrent access is the point of this test. + unsafe impl Sync for Racy {} + + static RACY: Racy = Racy(UnsafeCell::new(0)); + + /// Set by [`probe_console`] once KCSAN reported a data race in [`racy_inc`]. + static OBSERVED: Atomic<bool> = Atomic::new(false); + + #[inline(never)] + fn racy_inc() { + let p = RACY.0.get(); + // SAFETY: `p` is valid; the data race is intentional. `wrapping_add()` keeps the load and + // store in one basic block, so that the access is instrumented as a compound access (plain + // writes may be assumed atomic with `CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=y`). + unsafe { *p = (*p).wrapping_add(1); } + } + + fn contains(haystack: &[u8], needle: &[u8]) -> bool { + haystack.windows(needle.len()).any(|w| w == needle) + } + + /// Probe for the `console` tracepoint. + /// + /// # Safety + /// + /// `buf` must be non-null and valid for reads of `len` bytes. + unsafe extern "C" fn probe_console(_data: *mut c_void, buf: *const c_char, len: usize) { + // SAFETY: By the safety requirements of this function. + let line = unsafe { slice::from_raw_parts(buf.cast::<u8>(), len) }; + + if contains(line, b"BUG: KCSAN: data-race in ") && contains(line, b"racy_inc") { + OBSERVED.store(true, Relaxed); + } + } + + #[pin_data] + struct Ctx { + stop: Atomic<bool>, + #[pin] + done: Completion, + } + + #[test] + fn data_race() -> Result { + // Do not pass on a report from a previous run of this suite. + OBSERVED.store(false, Relaxed); + + let ctx = Arc::pin_init( + pin_init!(Ctx { + stop: Atomic::new(false), + done <- Completion::new(), + }), + GFP_KERNEL, + )?; + + // SAFETY: `probe_console` has the signature expected by the `console` tracepoint. Being + // part of the kernel image, it and `OBSERVED` outlive the registration, so there is no + // need to synchronize with in-flight probes after unregistering. + to_result(unsafe { + bindings::tracepoint_probe_register( + &raw mut bindings::__tracepoint_console, + probe_console as *mut c_void, + ptr::null_mut(), + ) + })?; + let _unregister = ScopeGuard::new(|| { + // SAFETY: The probe was registered above. + unsafe { + bindings::tracepoint_probe_unregister( + &raw mut bindings::__tracepoint_console, + probe_console as *mut c_void, + ptr::null_mut(), + ); + } + }); + + let worker = ctx.clone(); + workqueue::system_unbound().try_spawn(GFP_KERNEL, move || { + while !worker.stop.load(Relaxed) { + racy_inc(); + } + worker.done.complete_all(); + })?; + + let start = Instant::<Monotonic>::now(); + while !OBSERVED.load(Relaxed) && start.elapsed() < Delta::from_secs(10) { + racy_inc(); + } + + ctx.stop.store(true, Relaxed); + ctx.done.wait_for_completion(); + drop(_unregister); + + assert!(OBSERVED.load(Relaxed)); + Ok(()) + } +} diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index 4d5c96ddc49c..009efda9e7a4 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -94,6 +94,8 @@ pub mod iov; pub mod irq; pub mod jump_label; +#[cfg(CONFIG_RUST_KCSAN_KUNIT_TEST)] +mod kcsan_test; #[cfg(CONFIG_KUNIT)] pub mod kunit; pub mod list; -- 2.56.0.385.gd3acb90ef8-goog
