[PATCH v2 13/23] kcsan: selftest: Add test case to check memory barrier instrumentation

Marco Elver
2021-11-18T08:13:40Z

Memory barrier instrumentation is crucial to avoid false positives. To
avoid surprises, run a simple test case in the boot-time selftest to
ensure memory barriers are still instrumented correctly.

Signed-off-by: Marco Elver <elver@google.com>
---
kernel/kcsan/Makefile | 2 +
kernel/kcsan/selftest.c | 141 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 143 insertions(+)

diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
index c2bb07f5bcc7..ff47e896de3b 100644
--- a/kernel/kcsan/Makefile
+++ b/kernel/kcsan/Makefile
@@ -11,6 +11,8 @@ CFLAGS_core.o := $(call cc-option,-fno-conserve-stack) \
-fno-stack-protector -DDISABLE_BRANCH_PROFILING

obj-y := core.o debugfs.o report.o
+
+KCSAN_INSTRUMENT_BARRIERS_selftest.o := y
obj-$(CONFIG_KCSAN_SELFTEST) += selftest.o

CFLAGS_kcsan_test.o := $(CFLAGS_KCSAN) -g -fno-omit-frame-pointer
diff --git a/kernel/kcsan/selftest.c b/kernel/kcsan/selftest.c
index b4295a3892b7..08c6b84b9ebe 100644
--- a/kernel/kcsan/selftest.c
+++ b/kernel/kcsan/selftest.c
@@ -7,10 +7,15 @@

#define pr_fmt(fmt) "kcsan: " fmt

+#include <linux/atomic.h>
+#include <linux/bitops.h>
#include <linux/init.h>
+#include <linux/kcsan-checks.h>
#include <linux/kernel.h>
#include <linux/printk.h>
#include <linux/random.h>
+#include <linux/sched.h>
+#include <linux/spinlock.h>
#include <linux/types.h>

#include "encoding.h"
@@ -103,6 +108,141 @@ static bool __init test_matching_access(void)
return true;
}

+/*
+ * Correct memory barrier instrumentation is critical to avoiding false
+ * positives: simple test to check at boot certain barriers are always properly
+ * instrumented. See kcsan_test for a more complete test.
+ */
+static bool __init test_barrier(void)
+{
+#ifdef CONFIG_KCSAN_WEAK_MEMORY
+ struct kcsan_scoped_access *reorder_access = &current->kcsan_ctx.reorder_access;
+#else
+ struct kcsan_scoped_access *reorder_access = NULL;
+#endif
+ bool ret = true;
+ arch_spinlock_t arch_spinlock = __ARCH_SPIN_LOCK_UNLOCKED;
+ DEFINE_SPINLOCK(spinlock);
+ atomic_t dummy;
+ long test_var;
+
+ if (!reorder_access || !IS_ENABLED(CONFIG_SMP))
+ return true;
+
+#define __KCSAN_CHECK_BARRIER(access_type, barrier, name) \
+ do { \
+ reorder_access->type = (access_type) | KCSAN_ACCESS_SCOPED; \
+ reorder_access->size = 1; \
+ barrier; \
+ if (reorder_access->size != 0) { \
+ pr_err("improperly instrumented type=(" #access_type "): " name "\n"); \
+ ret = false; \
+ } \
+ } while (0)
+#define KCSAN_CHECK_READ_BARRIER(b) __KCSAN_CHECK_BARRIER(0, b, #b)
+#define KCSAN_CHECK_WRITE_BARRIER(b) __KCSAN_CHECK_BARRIER(KCSAN_ACCESS_WRITE, b, #b)
+#define KCSAN_CHECK_RW_BARRIER(b) __KCSAN_CHECK_BARRIER(KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND, b, #b)
+
+ kcsan_nestable_atomic_begin(); /* No watchpoints in called functions. */
+
+ KCSAN_CHECK_READ_BARRIER(mb());
+ KCSAN_CHECK_READ_BARRIER(rmb());
+ KCSAN_CHECK_READ_BARRIER(smp_mb());
+ KCSAN_CHECK_READ_BARRIER(smp_rmb());
+ KCSAN_CHECK_READ_BARRIER(dma_rmb());
+ KCSAN_CHECK_READ_BARRIER(smp_mb__before_atomic());
+ KCSAN_CHECK_READ_BARRIER(smp_mb__after_atomic());
+ KCSAN_CHECK_READ_BARRIER(smp_mb__after_spinlock());
+ KCSAN_CHECK_READ_BARRIER(smp_store_mb(test_var, 0));
+ KCSAN_CHECK_READ_BARRIER(smp_store_release(&test_var, 0));
+ KCSAN_CHECK_READ_BARRIER(xchg(&test_var, 0));
+ KCSAN_CHECK_READ_BARRIER(xchg_release(&test_var, 0));
+ KCSAN_CHECK_READ_BARRIER(cmpxchg(&test_var, 0, 0));
+ KCSAN_CHECK_READ_BARRIER(cmpxchg_release(&test_var, 0, 0));
+ KCSAN_CHECK_READ_BARRIER(atomic_set_release(&dummy, 0));
+ KCSAN_CHECK_READ_BARRIER(atomic_add_return(1, &dummy));
+ KCSAN_CHECK_READ_BARRIER(atomic_add_return_release(1, &dummy));
+ KCSAN_CHECK_READ_BARRIER(atomic_fetch_add(1, &dummy));
+ KCSAN_CHECK_READ_BARRIER(atomic_fetch_add_release(1, &dummy));
+ KCSAN_CHECK_READ_BARRIER(test_and_set_bit(0, &test_var));
+ KCSAN_CHECK_READ_BARRIER(test_and_clear_bit(0, &test_var));
+ KCSAN_CHECK_READ_BARRIER(test_and_change_bit(0, &test_var));
+ KCSAN_CHECK_READ_BARRIER(clear_bit_unlock(0, &test_var));
+ KCSAN_CHECK_READ_BARRIER(__clear_bit_unlock(0, &test_var));
+ KCSAN_CHECK_READ_BARRIER(clear_bit_unlock_is_negative_byte(0, &test_var));
+ arch_spin_lock(&arch_spinlock);
+ KCSAN_CHECK_READ_BARRIER(arch_spin_unlock(&arch_spinlock));
+ spin_lock(&spinlock);
+ KCSAN_CHECK_READ_BARRIER(spin_unlock(&spinlock));
+
+ KCSAN_CHECK_WRITE_BARRIER(mb());
+ KCSAN_CHECK_WRITE_BARRIER(wmb());
+ KCSAN_CHECK_WRITE_BARRIER(smp_mb());
+ KCSAN_CHECK_WRITE_BARRIER(smp_wmb());
+ KCSAN_CHECK_WRITE_BARRIER(dma_wmb());
+ KCSAN_CHECK_WRITE_BARRIER(smp_mb__before_atomic());
+ KCSAN_CHECK_WRITE_BARRIER(smp_mb__after_atomic());
+ KCSAN_CHECK_WRITE_BARRIER(smp_mb__after_spinlock());
+ KCSAN_CHECK_WRITE_BARRIER(smp_store_mb(test_var, 0));
+ KCSAN_CHECK_WRITE_BARRIER(smp_store_release(&test_var, 0));
+ KCSAN_CHECK_WRITE_BARRIER(xchg(&test_var, 0));
+ KCSAN_CHECK_WRITE_BARRIER(xchg_release(&test_var, 0));
+ KCSAN_CHECK_WRITE_BARRIER(cmpxchg(&test_var, 0, 0));
+ KCSAN_CHECK_WRITE_BARRIER(cmpxchg_release(&test_var, 0, 0));
+ KCSAN_CHECK_WRITE_BARRIER(atomic_set_release(&dummy, 0));
+ KCSAN_CHECK_WRITE_BARRIER(atomic_add_return(1, &dummy));
+ KCSAN_CHECK_WRITE_BARRIER(atomic_add_return_release(1, &dummy));
+ KCSAN_CHECK_WRITE_BARRIER(atomic_fetch_add(1, &dummy));
+ KCSAN_CHECK_WRITE_BARRIER(atomic_fetch_add_release(1, &dummy));
+ KCSAN_CHECK_WRITE_BARRIER(test_and_set_bit(0, &test_var));
+ KCSAN_CHECK_WRITE_BARRIER(test_and_clear_bit(0, &test_var));
+ KCSAN_CHECK_WRITE_BARRIER(test_and_change_bit(0, &test_var));
+ KCSAN_CHECK_WRITE_BARRIER(clear_bit_unlock(0, &test_var));
+ KCSAN_CHECK_WRITE_BARRIER(__clear_bit_unlock(0, &test_var));
+ KCSAN_CHECK_WRITE_BARRIER(clear_bit_unlock_is_negative_byte(0, &test_var));
+ arch_spin_lock(&arch_spinlock);
+ KCSAN_CHECK_WRITE_BARRIER(arch_spin_unlock(&arch_spinlock));
+ spin_lock(&spinlock);
+ KCSAN_CHECK_WRITE_BARRIER(spin_unlock(&spinlock));
+
+ KCSAN_CHECK_RW_BARRIER(mb());
+ KCSAN_CHECK_RW_BARRIER(wmb());
+ KCSAN_CHECK_RW_BARRIER(rmb());
+ KCSAN_CHECK_RW_BARRIER(smp_mb());
+ KCSAN_CHECK_RW_BARRIER(smp_wmb());
+ KCSAN_CHECK_RW_BARRIER(smp_rmb());
+ KCSAN_CHECK_RW_BARRIER(dma_wmb());
+ KCSAN_CHECK_RW_BARRIER(dma_rmb());
+ KCSAN_CHECK_RW_BARRIER(smp_mb__before_atomic());
+ KCSAN_CHECK_RW_BARRIER(smp_mb__after_atomic());
+ KCSAN_CHECK_RW_BARRIER(smp_mb__after_spinlock());
+ KCSAN_CHECK_RW_BARRIER(smp_store_mb(test_var, 0));
+ KCSAN_CHECK_RW_BARRIER(smp_store_release(&test_var, 0));
+ KCSAN_CHECK_RW_BARRIER(xchg(&test_var, 0));
+ KCSAN_CHECK_RW_BARRIER(xchg_release(&test_var, 0));
+ KCSAN_CHECK_RW_BARRIER(cmpxchg(&test_var, 0, 0));
+ KCSAN_CHECK_RW_BARRIER(cmpxchg_release(&test_var, 0, 0));
+ KCSAN_CHECK_RW_BARRIER(atomic_set_release(&dummy, 0));
+ KCSAN_CHECK_RW_BARRIER(atomic_add_return(1, &dummy));
+ KCSAN_CHECK_RW_BARRIER(atomic_add_return_release(1, &dummy));
+ KCSAN_CHECK_RW_BARRIER(atomic_fetch_add(1, &dummy));
+ KCSAN_CHECK_RW_BARRIER(atomic_fetch_add_release(1, &dummy));
+ KCSAN_CHECK_RW_BARRIER(test_and_set_bit(0, &test_var));
+ KCSAN_CHECK_RW_BARRIER(test_and_clear_bit(0, &test_var));
+ KCSAN_CHECK_RW_BARRIER(test_and_change_bit(0, &test_var));
+ KCSAN_CHECK_RW_BARRIER(clear_bit_unlock(0, &test_var));
+ KCSAN_CHECK_RW_BARRIER(__clear_bit_unlock(0, &test_var));
+ KCSAN_CHECK_RW_BARRIER(clear_bit_unlock_is_negative_byte(0, &test_var));
+ arch_spin_lock(&arch_spinlock);
+ KCSAN_CHECK_RW_BARRIER(arch_spin_unlock(&arch_spinlock));
+ spin_lock(&spinlock);
+ KCSAN_CHECK_RW_BARRIER(spin_unlock(&spinlock));
+
+ kcsan_nestable_atomic_end();
+
+ return ret;
+}
+
static int __init kcsan_selftest(void)
{
int passed = 0;
@@ -120,6 +260,7 @@ static int __init kcsan_selftest(void)
RUN_TEST(test_requires);
RUN_TEST(test_encode_decode);
RUN_TEST(test_matching_access);
+ RUN_TEST(test_barrier);

pr_info("selftest: %d/%d tests passed\n", passed, total);
if (passed != total)
--
2.34.0.rc2.393.gf8c9666880-goog