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kcsan: selftest: Add test case to check memory barrier instrumentation
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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 <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
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@melver @paulmckrcu
melver authored and paulmckrcu committed Dec 10, 2021
1 parent 116af35 commit 71b0e3a
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Showing 2 changed files with 143 additions and 0 deletions.
2 changes: 2 additions & 0 deletions kernel/kcsan/Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -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
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141 changes: 141 additions & 0 deletions kernel/kcsan/selftest.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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"
Expand Down Expand Up @@ -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;
Expand All @@ -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)
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