[PATCH v2 5/8] kcsan: Test support for compound instrumentation

Marco Elver
2020-07-24T07:00:51Z

Changes kcsan-test module to support checking reports that include
compound instrumentation. Since we should not fail the test if this
support is unavailable, we have to add a config variable that the test
can use to decide what to check for.

Signed-off-by: Marco Elver <elver@google.com>
---
v2:
* Fix CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE: s/--param -tsan/--param tsan/
---
kernel/kcsan/kcsan-test.c | 65 ++++++++++++++++++++++++++++++---------
lib/Kconfig.kcsan | 5 +++
2 files changed, 56 insertions(+), 14 deletions(-)

diff --git a/kernel/kcsan/kcsan-test.c b/kernel/kcsan/kcsan-test.c
index 721180cbbab1..ebe7fd245104 100644
--- a/kernel/kcsan/kcsan-test.c
+++ b/kernel/kcsan/kcsan-test.c
@@ -27,6 +27,12 @@
#include <linux/types.h>
#include <trace/events/printk.h>

+#ifdef CONFIG_CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE
+#define __KCSAN_ACCESS_RW(alt) (KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE)
+#else
+#define __KCSAN_ACCESS_RW(alt) (alt)
+#endif
+
/* Points to current test-case memory access "kernels". */
static void (*access_kernels[2])(void);

@@ -186,20 +192,21 @@ static bool report_matches(const struct expect_report *r)

/* Access 1 & 2 */
for (i = 0; i < 2; ++i) {
+ const int ty = r->access[i].type;
const char *const access_type =
- (r->access[i].type & KCSAN_ACCESS_ASSERT) ?
- ((r->access[i].type & KCSAN_ACCESS_WRITE) ?
- "assert no accesses" :
- "assert no writes") :
- ((r->access[i].type & KCSAN_ACCESS_WRITE) ?
- "write" :
- "read");
+ (ty & KCSAN_ACCESS_ASSERT) ?
+ ((ty & KCSAN_ACCESS_WRITE) ?
+ "assert no accesses" :
+ "assert no writes") :
+ ((ty & KCSAN_ACCESS_WRITE) ?
+ ((ty & KCSAN_ACCESS_COMPOUND) ?
+ "read-write" :
+ "write") :
+ "read");
const char *const access_type_aux =
- (r->access[i].type & KCSAN_ACCESS_ATOMIC) ?
- " (marked)" :
- ((r->access[i].type & KCSAN_ACCESS_SCOPED) ?
- " (scoped)" :
- "");
+ (ty & KCSAN_ACCESS_ATOMIC) ?
+ " (marked)" :
+ ((ty & KCSAN_ACCESS_SCOPED) ? " (scoped)" : "");

if (i == 1) {
/* Access 2 */
@@ -277,6 +284,12 @@ static noinline void test_kernel_write_atomic(void)
WRITE_ONCE(test_var, READ_ONCE_NOCHECK(test_sink) + 1);
}

+static noinline void test_kernel_atomic_rmw(void)
+{
+ /* Use builtin, so we can set up the "bad" atomic/non-atomic scenario. */
+ __atomic_fetch_add(&test_var, 1, __ATOMIC_RELAXED);
+}
+
__no_kcsan
static noinline void test_kernel_write_uninstrumented(void) { test_var++; }

@@ -439,8 +452,8 @@ static void test_concurrent_races(struct kunit *test)
const struct expect_report expect = {
.access = {
/* NULL will match any address. */
- { test_kernel_rmw_array, NULL, 0, KCSAN_ACCESS_WRITE },
- { test_kernel_rmw_array, NULL, 0, 0 },
+ { test_kernel_rmw_array, NULL, 0, __KCSAN_ACCESS_RW(KCSAN_ACCESS_WRITE) },
+ { test_kernel_rmw_array, NULL, 0, __KCSAN_ACCESS_RW(0) },
},
};
static const struct expect_report never = {
@@ -629,6 +642,29 @@ static void test_read_plain_atomic_write(struct kunit *test)
KUNIT_EXPECT_TRUE(test, match_expect);
}

+/* Test that atomic RMWs generate correct report. */
+__no_kcsan
+static void test_read_plain_atomic_rmw(struct kunit *test)
+{
+ const struct expect_report expect = {
+ .access = {
+ { test_kernel_read, &test_var, sizeof(test_var), 0 },
+ { test_kernel_atomic_rmw, &test_var, sizeof(test_var),
+ KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC },
+ },
+ };
+ bool match_expect = false;
+
+ if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS))
+ return;
+
+ begin_test_checks(test_kernel_read, test_kernel_atomic_rmw);
+ do {
+ match_expect = report_matches(&expect);
+ } while (!end_test_checks(match_expect));
+ KUNIT_EXPECT_TRUE(test, match_expect);
+}
+
/* Zero-sized accesses should never cause data race reports. */
__no_kcsan
static void test_zero_size_access(struct kunit *test)
@@ -942,6 +978,7 @@ static struct kunit_case kcsan_test_cases[] = {
KCSAN_KUNIT_CASE(test_write_write_struct_part),
KCSAN_KUNIT_CASE(test_read_atomic_write_atomic),
KCSAN_KUNIT_CASE(test_read_plain_atomic_write),
+ KCSAN_KUNIT_CASE(test_read_plain_atomic_rmw),
KCSAN_KUNIT_CASE(test_zero_size_access),
KCSAN_KUNIT_CASE(test_data_race),
KCSAN_KUNIT_CASE(test_assert_exclusive_writer),
diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
index 3d282d51849b..f271ff5fbb5a 100644
--- a/lib/Kconfig.kcsan
+++ b/lib/Kconfig.kcsan
@@ -40,6 +40,11 @@ menuconfig KCSAN

if KCSAN

+# Compiler capabilities that should not fail the test if they are unavailable.
+config CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE
+ def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-compound-read-before-write=1)) || \
+ (CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-compound-read-before-write=1))
+
config KCSAN_VERBOSE
bool "Show verbose reports with more information about system state"
depends on PROVE_LOCKING
--
2.28.0.rc0.142.g3c755180ce-goog