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Date:   Tue,  5 Oct 2021 12:58:55 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, "Paul E . McKenney" <paulmck@...nel.org>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Waiman Long <longman@...hat.com>,
        Will Deacon <will@...nel.org>, kasan-dev@...glegroups.com,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org
Subject: [PATCH -rcu/kcsan 13/23] kcsan: selftest: Add test case to check
 memory barrier instrumentation

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@...gle.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)
-- 
2.33.0.800.g4c38ced690-goog

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