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Message-ID: <20200506181405.GC2869@paulmck-ThinkPad-P72>
Date: Wed, 6 May 2020 11:14:05 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Marco Elver <elver@...gle.com>
Cc: dvyukov@...gle.com, glider@...gle.com, andreyknvl@...gle.com,
kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
kunit-dev@...glegroups.com, davidgow@...gle.com
Subject: Re: [PATCH v2] kcsan: Add test suite
On Tue, May 05, 2020 at 08:28:21PM +0200, Marco Elver wrote:
> This adds KCSAN test focusing on behaviour of the integrated runtime.
> Tests various race scenarios, and verifies the reports generated to
> console. Makes use of KUnit for test organization, and the Torture
> framework for test thread control.
>
> Signed-off-by: Marco Elver <elver@...gle.com>
I have replaced V1 with this update, thank you!
Thanx, Paul
> ---
> v2:
> * Add necessary precondition checks that we have sufficient online CPUs
> for PREEMPT_NONE, PREEMPT_VOLUNTARY, and PREEMPT without
> KCSAN_INTERRUPT_WATCHER. This is to avoid deadlocking the system, or
> resulting in flaky test results.
> * Adds the necessary might_sleep() for PREEMPT_VOLUNTARY.
> ---
> kernel/kcsan/Makefile | 3 +
> kernel/kcsan/kcsan-test.c | 1084 +++++++++++++++++++++++++++++++++++++
> lib/Kconfig.kcsan | 23 +-
> 3 files changed, 1109 insertions(+), 1 deletion(-)
> create mode 100644 kernel/kcsan/kcsan-test.c
>
> diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
> index d4999b38d1be..14533cf24bc3 100644
> --- a/kernel/kcsan/Makefile
> +++ b/kernel/kcsan/Makefile
> @@ -12,3 +12,6 @@ CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \
>
> obj-y := core.o debugfs.o report.o
> obj-$(CONFIG_KCSAN_SELFTEST) += test.o
> +
> +CFLAGS_kcsan-test.o := $(CFLAGS_KCSAN) -g -fno-omit-frame-pointer
> +obj-$(CONFIG_KCSAN_TEST) += kcsan-test.o
> diff --git a/kernel/kcsan/kcsan-test.c b/kernel/kcsan/kcsan-test.c
> new file mode 100644
> index 000000000000..a8c11506dd2a
> --- /dev/null
> +++ b/kernel/kcsan/kcsan-test.c
> @@ -0,0 +1,1084 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KCSAN test with various race scenarious to test runtime behaviour. Since the
> + * interface with which KCSAN's reports are obtained is via the console, this is
> + * the output we should verify. For each test case checks the presence (or
> + * absence) of generated reports. Relies on 'console' tracepoint to capture
> + * reports as they appear in the kernel log.
> + *
> + * Makes use of KUnit for test organization, and the Torture framework for test
> + * thread control.
> + *
> + * Copyright (C) 2020, Google LLC.
> + * Author: Marco Elver <elver@...gle.com>
> + */
> +
> +#include <kunit/test.h>
> +#include <linux/jiffies.h>
> +#include <linux/kcsan-checks.h>
> +#include <linux/kernel.h>
> +#include <linux/sched.h>
> +#include <linux/seqlock.h>
> +#include <linux/spinlock.h>
> +#include <linux/string.h>
> +#include <linux/timer.h>
> +#include <linux/torture.h>
> +#include <linux/tracepoint.h>
> +#include <linux/types.h>
> +#include <trace/events/printk.h>
> +
> +/* Points to current test-case memory access "kernels". */
> +static void (*access_kernels[2])(void);
> +
> +static struct task_struct **threads; /* Lists of threads. */
> +static unsigned long end_time; /* End time of test. */
> +
> +/* Report as observed from console. */
> +static struct {
> + spinlock_t lock;
> + int nlines;
> + char lines[3][512];
> +} observed = {
> + .lock = __SPIN_LOCK_UNLOCKED(observed.lock),
> +};
> +
> +/* Setup test checking loop. */
> +static __no_kcsan_or_inline void
> +begin_test_checks(void (*func1)(void), void (*func2)(void))
> +{
> + kcsan_disable_current();
> +
> + /*
> + * Require at least as long as KCSAN_REPORT_ONCE_IN_MS, to ensure at
> + * least one race is reported.
> + */
> + end_time = jiffies + msecs_to_jiffies(CONFIG_KCSAN_REPORT_ONCE_IN_MS + 500);
> +
> + /* Signal start; release potential initialization of shared data. */
> + smp_store_release(&access_kernels[0], func1);
> + smp_store_release(&access_kernels[1], func2);
> +}
> +
> +/* End test checking loop. */
> +static __no_kcsan_or_inline bool
> +end_test_checks(bool stop)
> +{
> + if (!stop && time_before(jiffies, end_time)) {
> + /* Continue checking */
> + might_sleep();
> + return false;
> + }
> +
> + kcsan_enable_current();
> + return true;
> +}
> +
> +/*
> + * Probe for console output: checks if a race was reported, and obtains observed
> + * lines of interest.
> + */
> +__no_kcsan
> +static void probe_console(void *ignore, const char *buf, size_t len)
> +{
> + unsigned long flags;
> + int nlines;
> +
> + /*
> + * Note that KCSAN reports under a global lock, so we do not risk the
> + * possibility of having multiple reports interleaved. If that were the
> + * case, we'd expect tests to fail.
> + */
> +
> + spin_lock_irqsave(&observed.lock, flags);
> + nlines = observed.nlines;
> +
> + if (strnstr(buf, "BUG: KCSAN: ", len) && strnstr(buf, "test_", len)) {
> + /*
> + * KCSAN report and related to the test.
> + *
> + * The provided @buf is not NUL-terminated; copy no more than
> + * @len bytes and let strscpy() add the missing NUL-terminator.
> + */
> + strscpy(observed.lines[0], buf, min(len + 1, sizeof(observed.lines[0])));
> + nlines = 1;
> + } else if ((nlines == 1 || nlines == 2) && strnstr(buf, "bytes by", len)) {
> + strscpy(observed.lines[nlines++], buf, min(len + 1, sizeof(observed.lines[0])));
> +
> + if (strnstr(buf, "race at unknown origin", len)) {
> + if (WARN_ON(nlines != 2))
> + goto out;
> +
> + /* No second line of interest. */
> + strcpy(observed.lines[nlines++], "<none>");
> + }
> + }
> +
> +out:
> + WRITE_ONCE(observed.nlines, nlines); /* Publish new nlines. */
> + spin_unlock_irqrestore(&observed.lock, flags);
> +}
> +
> +/* Check if a report related to the test exists. */
> +__no_kcsan
> +static bool report_available(void)
> +{
> + return READ_ONCE(observed.nlines) == ARRAY_SIZE(observed.lines);
> +}
> +
> +/* Report information we expect in a report. */
> +struct expect_report {
> + /* Access information of both accesses. */
> + struct {
> + void *fn; /* Function pointer to expected function of top frame. */
> + void *addr; /* Address of access; unchecked if NULL. */
> + size_t size; /* Size of access; unchecked if @addr is NULL. */
> + int type; /* Access type, see KCSAN_ACCESS definitions. */
> + } access[2];
> +};
> +
> +/* Check observed report matches information in @r. */
> +__no_kcsan
> +static bool report_matches(const struct expect_report *r)
> +{
> + const bool is_assert = (r->access[0].type | r->access[1].type) & KCSAN_ACCESS_ASSERT;
> + bool ret = false;
> + unsigned long flags;
> + typeof(observed.lines) expect;
> + const char *end;
> + char *cur;
> + int i;
> +
> + /* Doubled-checked locking. */
> + if (!report_available())
> + return false;
> +
> + /* Generate expected report contents. */
> +
> + /* Title */
> + cur = expect[0];
> + end = &expect[0][sizeof(expect[0]) - 1];
> + cur += scnprintf(cur, end - cur, "BUG: KCSAN: %s in ",
> + is_assert ? "assert: race" : "data-race");
> + if (r->access[1].fn) {
> + char tmp[2][64];
> + int cmp;
> +
> + /* Expect lexographically sorted function names in title. */
> + scnprintf(tmp[0], sizeof(tmp[0]), "%pS", r->access[0].fn);
> + scnprintf(tmp[1], sizeof(tmp[1]), "%pS", r->access[1].fn);
> + cmp = strcmp(tmp[0], tmp[1]);
> + cur += scnprintf(cur, end - cur, "%ps / %ps",
> + cmp < 0 ? r->access[0].fn : r->access[1].fn,
> + cmp < 0 ? r->access[1].fn : r->access[0].fn);
> + } else {
> + scnprintf(cur, end - cur, "%pS", r->access[0].fn);
> + /* The exact offset won't match, remove it. */
> + cur = strchr(expect[0], '+');
> + if (cur)
> + *cur = '\0';
> + }
> +
> + /* Access 1 */
> + cur = expect[1];
> + end = &expect[1][sizeof(expect[1]) - 1];
> + if (!r->access[1].fn)
> + cur += scnprintf(cur, end - cur, "race at unknown origin, with ");
> +
> + /* Access 1 & 2 */
> + for (i = 0; i < 2; ++i) {
> + 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");
> + const char *const access_type_aux =
> + (r->access[i].type & KCSAN_ACCESS_ATOMIC) ?
> + " (marked)" :
> + ((r->access[i].type & KCSAN_ACCESS_SCOPED) ?
> + " (scoped)" :
> + "");
> +
> + if (i == 1) {
> + /* Access 2 */
> + cur = expect[2];
> + end = &expect[2][sizeof(expect[2]) - 1];
> +
> + if (!r->access[1].fn) {
> + /* Dummy string if no second access is available. */
> + strcpy(cur, "<none>");
> + break;
> + }
> + }
> +
> + cur += scnprintf(cur, end - cur, "%s%s to ", access_type,
> + access_type_aux);
> +
> + if (r->access[i].addr) /* Address is optional. */
> + cur += scnprintf(cur, end - cur, "0x%px of %zu bytes",
> + r->access[i].addr, r->access[i].size);
> + }
> +
> + spin_lock_irqsave(&observed.lock, flags);
> + if (!report_available())
> + goto out; /* A new report is being captured. */
> +
> + /* Finally match expected output to what we actually observed. */
> + ret = strstr(observed.lines[0], expect[0]) &&
> + /* Access info may appear in any order. */
> + ((strstr(observed.lines[1], expect[1]) &&
> + strstr(observed.lines[2], expect[2])) ||
> + (strstr(observed.lines[1], expect[2]) &&
> + strstr(observed.lines[2], expect[1])));
> +out:
> + spin_unlock_irqrestore(&observed.lock, flags);
> + return ret;
> +}
> +
> +/* ===== Test kernels ===== */
> +
> +static long test_sink;
> +static long test_var;
> +/* @test_array should be large enough to fall into multiple watchpoint slots. */
> +static long test_array[3 * PAGE_SIZE / sizeof(long)];
> +static struct {
> + long val[8];
> +} test_struct;
> +static DEFINE_SEQLOCK(test_seqlock);
> +
> +/*
> + * Helper to avoid compiler optimizing out reads, and to generate source values
> + * for writes.
> + */
> +__no_kcsan
> +static noinline void sink_value(long v) { WRITE_ONCE(test_sink, v); }
> +
> +static noinline void test_kernel_read(void) { sink_value(test_var); }
> +
> +static noinline void test_kernel_write(void)
> +{
> + test_var = READ_ONCE_NOCHECK(test_sink) + 1;
> +}
> +
> +static noinline void test_kernel_write_nochange(void) { test_var = 42; }
> +
> +/* Suffixed by value-change exception filter. */
> +static noinline void test_kernel_write_nochange_rcu(void) { test_var = 42; }
> +
> +static noinline void test_kernel_read_atomic(void)
> +{
> + sink_value(READ_ONCE(test_var));
> +}
> +
> +static noinline void test_kernel_write_atomic(void)
> +{
> + WRITE_ONCE(test_var, READ_ONCE_NOCHECK(test_sink) + 1);
> +}
> +
> +__no_kcsan
> +static noinline void test_kernel_write_uninstrumented(void) { test_var++; }
> +
> +static noinline void test_kernel_data_race(void) { data_race(test_var++); }
> +
> +static noinline void test_kernel_assert_writer(void)
> +{
> + ASSERT_EXCLUSIVE_WRITER(test_var);
> +}
> +
> +static noinline void test_kernel_assert_access(void)
> +{
> + ASSERT_EXCLUSIVE_ACCESS(test_var);
> +}
> +
> +#define TEST_CHANGE_BITS 0xff00ff00
> +
> +static noinline void test_kernel_change_bits(void)
> +{
> + if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {
> + /*
> + * Avoid race of unknown origin for this test, just pretend they
> + * are atomic.
> + */
> + kcsan_nestable_atomic_begin();
> + test_var ^= TEST_CHANGE_BITS;
> + kcsan_nestable_atomic_end();
> + } else
> + WRITE_ONCE(test_var, READ_ONCE(test_var) ^ TEST_CHANGE_BITS);
> +}
> +
> +static noinline void test_kernel_assert_bits_change(void)
> +{
> + ASSERT_EXCLUSIVE_BITS(test_var, TEST_CHANGE_BITS);
> +}
> +
> +static noinline void test_kernel_assert_bits_nochange(void)
> +{
> + ASSERT_EXCLUSIVE_BITS(test_var, ~TEST_CHANGE_BITS);
> +}
> +
> +/* To check that scoped assertions do trigger anywhere in scope. */
> +static noinline void test_enter_scope(void)
> +{
> + int x = 0;
> +
> + /* Unrelated accesses to scoped assert. */
> + READ_ONCE(test_sink);
> + kcsan_check_read(&x, sizeof(x));
> +}
> +
> +static noinline void test_kernel_assert_writer_scoped(void)
> +{
> + ASSERT_EXCLUSIVE_WRITER_SCOPED(test_var);
> + test_enter_scope();
> +}
> +
> +static noinline void test_kernel_assert_access_scoped(void)
> +{
> + ASSERT_EXCLUSIVE_ACCESS_SCOPED(test_var);
> + test_enter_scope();
> +}
> +
> +static noinline void test_kernel_rmw_array(void)
> +{
> + int i;
> +
> + for (i = 0; i < ARRAY_SIZE(test_array); ++i)
> + test_array[i]++;
> +}
> +
> +static noinline void test_kernel_write_struct(void)
> +{
> + kcsan_check_write(&test_struct, sizeof(test_struct));
> + kcsan_disable_current();
> + test_struct.val[3]++; /* induce value change */
> + kcsan_enable_current();
> +}
> +
> +static noinline void test_kernel_write_struct_part(void)
> +{
> + test_struct.val[3] = 42;
> +}
> +
> +static noinline void test_kernel_read_struct_zero_size(void)
> +{
> + kcsan_check_read(&test_struct.val[3], 0);
> +}
> +
> +static noinline void test_kernel_seqlock_reader(void)
> +{
> + unsigned int seq;
> +
> + do {
> + seq = read_seqbegin(&test_seqlock);
> + sink_value(test_var);
> + } while (read_seqretry(&test_seqlock, seq));
> +}
> +
> +static noinline void test_kernel_seqlock_writer(void)
> +{
> + unsigned long flags;
> +
> + write_seqlock_irqsave(&test_seqlock, flags);
> + test_var++;
> + write_sequnlock_irqrestore(&test_seqlock, flags);
> +}
> +
> +/* ===== Test cases ===== */
> +
> +/* Simple test with normal data race. */
> +__no_kcsan
> +static void test_basic(struct kunit *test)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_write, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> + { test_kernel_read, &test_var, sizeof(test_var), 0 },
> + },
> + };
> + static const struct expect_report never = {
> + .access = {
> + { test_kernel_read, &test_var, sizeof(test_var), 0 },
> + { test_kernel_read, &test_var, sizeof(test_var), 0 },
> + },
> + };
> + bool match_expect = false;
> + bool match_never = false;
> +
> + begin_test_checks(test_kernel_write, test_kernel_read);
> + do {
> + match_expect |= report_matches(&expect);
> + match_never = report_matches(&never);
> + } while (!end_test_checks(match_never));
> + KUNIT_EXPECT_TRUE(test, match_expect);
> + KUNIT_EXPECT_FALSE(test, match_never);
> +}
> +
> +/*
> + * Stress KCSAN with lots of concurrent races on different addresses until
> + * timeout.
> + */
> +__no_kcsan
> +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 },
> + },
> + };
> + static const struct expect_report never = {
> + .access = {
> + { test_kernel_rmw_array, NULL, 0, 0 },
> + { test_kernel_rmw_array, NULL, 0, 0 },
> + },
> + };
> + bool match_expect = false;
> + bool match_never = false;
> +
> + begin_test_checks(test_kernel_rmw_array, test_kernel_rmw_array);
> + do {
> + match_expect |= report_matches(&expect);
> + match_never |= report_matches(&never);
> + } while (!end_test_checks(false));
> + KUNIT_EXPECT_TRUE(test, match_expect); /* Sanity check matches exist. */
> + KUNIT_EXPECT_FALSE(test, match_never);
> +}
> +
> +/* Test the KCSAN_REPORT_VALUE_CHANGE_ONLY option. */
> +__no_kcsan
> +static void test_novalue_change(struct kunit *test)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> + { test_kernel_read, &test_var, sizeof(test_var), 0 },
> + },
> + };
> + bool match_expect = false;
> +
> + begin_test_checks(test_kernel_write_nochange, test_kernel_read);
> + do {
> + match_expect = report_matches(&expect);
> + } while (!end_test_checks(match_expect));
> + if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY))
> + KUNIT_EXPECT_FALSE(test, match_expect);
> + else
> + KUNIT_EXPECT_TRUE(test, match_expect);
> +}
> +
> +/*
> + * Test that the rules where the KCSAN_REPORT_VALUE_CHANGE_ONLY option should
> + * never apply work.
> + */
> +__no_kcsan
> +static void test_novalue_change_exception(struct kunit *test)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_write_nochange_rcu, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> + { test_kernel_read, &test_var, sizeof(test_var), 0 },
> + },
> + };
> + bool match_expect = false;
> +
> + begin_test_checks(test_kernel_write_nochange_rcu, test_kernel_read);
> + do {
> + match_expect = report_matches(&expect);
> + } while (!end_test_checks(match_expect));
> + KUNIT_EXPECT_TRUE(test, match_expect);
> +}
> +
> +/* Test that data races of unknown origin are reported. */
> +__no_kcsan
> +static void test_unknown_origin(struct kunit *test)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_read, &test_var, sizeof(test_var), 0 },
> + { NULL },
> + },
> + };
> + bool match_expect = false;
> +
> + begin_test_checks(test_kernel_write_uninstrumented, test_kernel_read);
> + do {
> + match_expect = report_matches(&expect);
> + } while (!end_test_checks(match_expect));
> + if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN))
> + KUNIT_EXPECT_TRUE(test, match_expect);
> + else
> + KUNIT_EXPECT_FALSE(test, match_expect);
> +}
> +
> +/* Test KCSAN_ASSUME_PLAIN_WRITES_ATOMIC if it is selected. */
> +__no_kcsan
> +static void test_write_write_assume_atomic(struct kunit *test)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_write, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> + { test_kernel_write, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> + },
> + };
> + bool match_expect = false;
> +
> + begin_test_checks(test_kernel_write, test_kernel_write);
> + do {
> + sink_value(READ_ONCE(test_var)); /* induce value-change */
> + match_expect = report_matches(&expect);
> + } while (!end_test_checks(match_expect));
> + if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC))
> + KUNIT_EXPECT_FALSE(test, match_expect);
> + else
> + KUNIT_EXPECT_TRUE(test, match_expect);
> +}
> +
> +/*
> + * Test that data races with writes larger than word-size are always reported,
> + * even if KCSAN_ASSUME_PLAIN_WRITES_ATOMIC is selected.
> + */
> +__no_kcsan
> +static void test_write_write_struct(struct kunit *test)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> + { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> + },
> + };
> + bool match_expect = false;
> +
> + begin_test_checks(test_kernel_write_struct, test_kernel_write_struct);
> + do {
> + match_expect = report_matches(&expect);
> + } while (!end_test_checks(match_expect));
> + KUNIT_EXPECT_TRUE(test, match_expect);
> +}
> +
> +/*
> + * Test that data races where only one write is larger than word-size are always
> + * reported, even if KCSAN_ASSUME_PLAIN_WRITES_ATOMIC is selected.
> + */
> +__no_kcsan
> +static void test_write_write_struct_part(struct kunit *test)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> + { test_kernel_write_struct_part, &test_struct.val[3], sizeof(test_struct.val[3]), KCSAN_ACCESS_WRITE },
> + },
> + };
> + bool match_expect = false;
> +
> + begin_test_checks(test_kernel_write_struct, test_kernel_write_struct_part);
> + do {
> + match_expect = report_matches(&expect);
> + } while (!end_test_checks(match_expect));
> + KUNIT_EXPECT_TRUE(test, match_expect);
> +}
> +
> +/* Test that races with atomic accesses never result in reports. */
> +__no_kcsan
> +static void test_read_atomic_write_atomic(struct kunit *test)
> +{
> + bool match_never = false;
> +
> + begin_test_checks(test_kernel_read_atomic, test_kernel_write_atomic);
> + do {
> + match_never = report_available();
> + } while (!end_test_checks(match_never));
> + KUNIT_EXPECT_FALSE(test, match_never);
> +}
> +
> +/* Test that a race with an atomic and plain access result in reports. */
> +__no_kcsan
> +static void test_read_plain_atomic_write(struct kunit *test)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_read, &test_var, sizeof(test_var), 0 },
> + { test_kernel_write_atomic, &test_var, sizeof(test_var), 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_write_atomic);
> + 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)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> + { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> + },
> + };
> + const struct expect_report never = {
> + .access = {
> + { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> + { test_kernel_read_struct_zero_size, &test_struct.val[3], 0, 0 },
> + },
> + };
> + bool match_expect = false;
> + bool match_never = false;
> +
> + begin_test_checks(test_kernel_write_struct, test_kernel_read_struct_zero_size);
> + do {
> + match_expect |= report_matches(&expect);
> + match_never = report_matches(&never);
> + } while (!end_test_checks(match_never));
> + KUNIT_EXPECT_TRUE(test, match_expect); /* Sanity check. */
> + KUNIT_EXPECT_FALSE(test, match_never);
> +}
> +
> +/* Test the data_race() macro. */
> +__no_kcsan
> +static void test_data_race(struct kunit *test)
> +{
> + bool match_never = false;
> +
> + begin_test_checks(test_kernel_data_race, test_kernel_data_race);
> + do {
> + match_never = report_available();
> + } while (!end_test_checks(match_never));
> + KUNIT_EXPECT_FALSE(test, match_never);
> +}
> +
> +__no_kcsan
> +static void test_assert_exclusive_writer(struct kunit *test)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
> + { test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> + },
> + };
> + bool match_expect = false;
> +
> + begin_test_checks(test_kernel_assert_writer, test_kernel_write_nochange);
> + do {
> + match_expect = report_matches(&expect);
> + } while (!end_test_checks(match_expect));
> + KUNIT_EXPECT_TRUE(test, match_expect);
> +}
> +
> +__no_kcsan
> +static void test_assert_exclusive_access(struct kunit *test)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
> + { test_kernel_read, &test_var, sizeof(test_var), 0 },
> + },
> + };
> + bool match_expect = false;
> +
> + begin_test_checks(test_kernel_assert_access, test_kernel_read);
> + do {
> + match_expect = report_matches(&expect);
> + } while (!end_test_checks(match_expect));
> + KUNIT_EXPECT_TRUE(test, match_expect);
> +}
> +
> +__no_kcsan
> +static void test_assert_exclusive_access_writer(struct kunit *test)
> +{
> + const struct expect_report expect_access_writer = {
> + .access = {
> + { test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
> + { test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
> + },
> + };
> + const struct expect_report expect_access_access = {
> + .access = {
> + { test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
> + { test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
> + },
> + };
> + const struct expect_report never = {
> + .access = {
> + { test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
> + { test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
> + },
> + };
> + bool match_expect_access_writer = false;
> + bool match_expect_access_access = false;
> + bool match_never = false;
> +
> + begin_test_checks(test_kernel_assert_access, test_kernel_assert_writer);
> + do {
> + match_expect_access_writer |= report_matches(&expect_access_writer);
> + match_expect_access_access |= report_matches(&expect_access_access);
> + match_never |= report_matches(&never);
> + } while (!end_test_checks(match_never));
> + KUNIT_EXPECT_TRUE(test, match_expect_access_writer);
> + KUNIT_EXPECT_TRUE(test, match_expect_access_access);
> + KUNIT_EXPECT_FALSE(test, match_never);
> +}
> +
> +__no_kcsan
> +static void test_assert_exclusive_bits_change(struct kunit *test)
> +{
> + const struct expect_report expect = {
> + .access = {
> + { test_kernel_assert_bits_change, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
> + { test_kernel_change_bits, &test_var, sizeof(test_var),
> + KCSAN_ACCESS_WRITE | (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) ? 0 : KCSAN_ACCESS_ATOMIC) },
> + },
> + };
> + bool match_expect = false;
> +
> + begin_test_checks(test_kernel_assert_bits_change, test_kernel_change_bits);
> + do {
> + match_expect = report_matches(&expect);
> + } while (!end_test_checks(match_expect));
> + KUNIT_EXPECT_TRUE(test, match_expect);
> +}
> +
> +__no_kcsan
> +static void test_assert_exclusive_bits_nochange(struct kunit *test)
> +{
> + bool match_never = false;
> +
> + begin_test_checks(test_kernel_assert_bits_nochange, test_kernel_change_bits);
> + do {
> + match_never = report_available();
> + } while (!end_test_checks(match_never));
> + KUNIT_EXPECT_FALSE(test, match_never);
> +}
> +
> +__no_kcsan
> +static void test_assert_exclusive_writer_scoped(struct kunit *test)
> +{
> + const struct expect_report expect_start = {
> + .access = {
> + { test_kernel_assert_writer_scoped, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_SCOPED },
> + { test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> + },
> + };
> + const struct expect_report expect_anywhere = {
> + .access = {
> + { test_enter_scope, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_SCOPED },
> + { test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> + },
> + };
> + bool match_expect_start = false;
> + bool match_expect_anywhere = false;
> +
> + begin_test_checks(test_kernel_assert_writer_scoped, test_kernel_write_nochange);
> + do {
> + match_expect_start |= report_matches(&expect_start);
> + match_expect_anywhere |= report_matches(&expect_anywhere);
> + } while (!end_test_checks(match_expect_start && match_expect_anywhere));
> + KUNIT_EXPECT_TRUE(test, match_expect_start);
> + KUNIT_EXPECT_TRUE(test, match_expect_anywhere);
> +}
> +
> +__no_kcsan
> +static void test_assert_exclusive_access_scoped(struct kunit *test)
> +{
> + const struct expect_report expect_start1 = {
> + .access = {
> + { test_kernel_assert_access_scoped, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_SCOPED },
> + { test_kernel_read, &test_var, sizeof(test_var), 0 },
> + },
> + };
> + const struct expect_report expect_start2 = {
> + .access = { expect_start1.access[0], expect_start1.access[0] },
> + };
> + const struct expect_report expect_inscope = {
> + .access = {
> + { test_enter_scope, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_SCOPED },
> + { test_kernel_read, &test_var, sizeof(test_var), 0 },
> + },
> + };
> + bool match_expect_start = false;
> + bool match_expect_inscope = false;
> +
> + begin_test_checks(test_kernel_assert_access_scoped, test_kernel_read);
> + end_time += msecs_to_jiffies(1000); /* This test requires a bit more time. */
> + do {
> + match_expect_start |= report_matches(&expect_start1) || report_matches(&expect_start2);
> + match_expect_inscope |= report_matches(&expect_inscope);
> + } while (!end_test_checks(match_expect_start && match_expect_inscope));
> + KUNIT_EXPECT_TRUE(test, match_expect_start);
> + KUNIT_EXPECT_TRUE(test, match_expect_inscope);
> +}
> +
> +/* Test that racing accesses in seqlock critical sections are not reported. */
> +__no_kcsan
> +static void test_seqlock_noreport(struct kunit *test)
> +{
> + bool match_never = false;
> +
> + begin_test_checks(test_kernel_seqlock_reader, test_kernel_seqlock_writer);
> + do {
> + match_never = report_available();
> + } while (!end_test_checks(match_never));
> + KUNIT_EXPECT_FALSE(test, match_never);
> +}
> +
> +/*
> + * Each test case is run with different numbers of threads. Until KUnit supports
> + * passing arguments for each test case, we encode #threads in the test case
> + * name (read by get_num_threads()). [The '-' was chosen as a stylistic
> + * preference to separate test name and #threads.]
> + *
> + * The thread counts are chosen to cover potentially interesting boundaries and
> + * corner cases (range 2-5), and then stress the system with larger counts.
> + */
> +#define KCSAN_KUNIT_CASE(test_name) \
> + { .run_case = test_name, .name = #test_name "-02" }, \
> + { .run_case = test_name, .name = #test_name "-03" }, \
> + { .run_case = test_name, .name = #test_name "-04" }, \
> + { .run_case = test_name, .name = #test_name "-05" }, \
> + { .run_case = test_name, .name = #test_name "-08" }, \
> + { .run_case = test_name, .name = #test_name "-16" }
> +
> +static struct kunit_case kcsan_test_cases[] = {
> + KCSAN_KUNIT_CASE(test_basic),
> + KCSAN_KUNIT_CASE(test_concurrent_races),
> + KCSAN_KUNIT_CASE(test_novalue_change),
> + KCSAN_KUNIT_CASE(test_novalue_change_exception),
> + KCSAN_KUNIT_CASE(test_unknown_origin),
> + KCSAN_KUNIT_CASE(test_write_write_assume_atomic),
> + KCSAN_KUNIT_CASE(test_write_write_struct),
> + 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_zero_size_access),
> + KCSAN_KUNIT_CASE(test_data_race),
> + KCSAN_KUNIT_CASE(test_assert_exclusive_writer),
> + KCSAN_KUNIT_CASE(test_assert_exclusive_access),
> + KCSAN_KUNIT_CASE(test_assert_exclusive_access_writer),
> + KCSAN_KUNIT_CASE(test_assert_exclusive_bits_change),
> + KCSAN_KUNIT_CASE(test_assert_exclusive_bits_nochange),
> + KCSAN_KUNIT_CASE(test_assert_exclusive_writer_scoped),
> + KCSAN_KUNIT_CASE(test_assert_exclusive_access_scoped),
> + KCSAN_KUNIT_CASE(test_seqlock_noreport),
> + {},
> +};
> +
> +/* ===== End test cases ===== */
> +
> +/* Get number of threads encoded in test name. */
> +static bool __no_kcsan
> +get_num_threads(const char *test, int *nthreads)
> +{
> + int len = strlen(test);
> +
> + if (WARN_ON(len < 3))
> + return false;
> +
> + *nthreads = test[len - 1] - '0';
> + *nthreads += (test[len - 2] - '0') * 10;
> +
> + if (WARN_ON(*nthreads < 0))
> + return false;
> +
> + return true;
> +}
> +
> +/* Concurrent accesses from interrupts. */
> +__no_kcsan
> +static void access_thread_timer(struct timer_list *timer)
> +{
> + static atomic_t cnt = ATOMIC_INIT(0);
> + unsigned int idx;
> + void (*func)(void);
> +
> + idx = (unsigned int)atomic_inc_return(&cnt) % ARRAY_SIZE(access_kernels);
> + /* Acquire potential initialization. */
> + func = smp_load_acquire(&access_kernels[idx]);
> + if (func)
> + func();
> +}
> +
> +/* The main loop for each thread. */
> +__no_kcsan
> +static int access_thread(void *arg)
> +{
> + struct timer_list timer;
> + unsigned int cnt = 0;
> + unsigned int idx;
> + void (*func)(void);
> +
> + timer_setup_on_stack(&timer, access_thread_timer, 0);
> + do {
> + might_sleep();
> +
> + if (!timer_pending(&timer))
> + mod_timer(&timer, jiffies + 1);
> + else {
> + /* Iterate through all kernels. */
> + idx = cnt++ % ARRAY_SIZE(access_kernels);
> + /* Acquire potential initialization. */
> + func = smp_load_acquire(&access_kernels[idx]);
> + if (func)
> + func();
> + }
> + } while (!torture_must_stop());
> + del_timer_sync(&timer);
> + destroy_timer_on_stack(&timer);
> +
> + torture_kthread_stopping("access_thread");
> + return 0;
> +}
> +
> +__no_kcsan
> +static int test_init(struct kunit *test)
> +{
> + unsigned long flags;
> + int nthreads;
> + int i;
> +
> + spin_lock_irqsave(&observed.lock, flags);
> + for (i = 0; i < ARRAY_SIZE(observed.lines); ++i)
> + observed.lines[i][0] = '\0';
> + observed.nlines = 0;
> + spin_unlock_irqrestore(&observed.lock, flags);
> +
> + if (!torture_init_begin((char *)test->name, 1))
> + return -EBUSY;
> +
> + if (!get_num_threads(test->name, &nthreads))
> + goto err;
> +
> + if (WARN_ON(threads))
> + goto err;
> +
> + for (i = 0; i < ARRAY_SIZE(access_kernels); ++i) {
> + if (WARN_ON(access_kernels[i]))
> + goto err;
> + }
> +
> + if (!IS_ENABLED(CONFIG_PREEMPT) || !IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER)) {
> + /*
> + * Without any preemption, keep 2 CPUs free for other tasks, one
> + * of which is the main test case function checking for
> + * completion or failure.
> + */
> + const int min_unused_cpus = IS_ENABLED(CONFIG_PREEMPT_NONE) ? 2 : 0;
> + const int min_required_cpus = 2 + min_unused_cpus;
> +
> + if (num_online_cpus() < min_required_cpus) {
> + pr_err("%s: too few online CPUs (%u < %d) for test",
> + test->name, num_online_cpus(), min_required_cpus);
> + goto err;
> + } else if (nthreads > num_online_cpus() - min_unused_cpus) {
> + nthreads = num_online_cpus() - min_unused_cpus;
> + pr_warn("%s: limiting number of threads to %d\n",
> + test->name, nthreads);
> + }
> + }
> +
> + if (nthreads) {
> + threads = kcalloc(nthreads + 1, sizeof(struct task_struct *),
> + GFP_KERNEL);
> + if (WARN_ON(!threads))
> + goto err;
> +
> + threads[nthreads] = NULL;
> + for (i = 0; i < nthreads; ++i) {
> + if (torture_create_kthread(access_thread, NULL,
> + threads[i]))
> + goto err;
> + }
> + }
> +
> + torture_init_end();
> +
> + return 0;
> +
> +err:
> + kfree(threads);
> + threads = NULL;
> + torture_init_end();
> + return -EINVAL;
> +}
> +
> +__no_kcsan
> +static void test_exit(struct kunit *test)
> +{
> + struct task_struct **stop_thread;
> + int i;
> +
> + if (torture_cleanup_begin())
> + return;
> +
> + for (i = 0; i < ARRAY_SIZE(access_kernels); ++i)
> + WRITE_ONCE(access_kernels[i], NULL);
> +
> + if (threads) {
> + for (stop_thread = threads; *stop_thread; stop_thread++)
> + torture_stop_kthread(reader_thread, *stop_thread);
> +
> + kfree(threads);
> + threads = NULL;
> + }
> +
> + torture_cleanup_end();
> +}
> +
> +static struct kunit_suite kcsan_test_suite = {
> + .name = "kcsan-test",
> + .test_cases = kcsan_test_cases,
> + .init = test_init,
> + .exit = test_exit,
> +};
> +static struct kunit_suite *kcsan_test_suites[] = { &kcsan_test_suite, NULL };
> +
> +__no_kcsan
> +static void register_tracepoints(struct tracepoint *tp, void *ignore)
> +{
> + check_trace_callback_type_console(probe_console);
> + if (!strcmp(tp->name, "console"))
> + WARN_ON(tracepoint_probe_register(tp, probe_console, NULL));
> +}
> +
> +__no_kcsan
> +static void unregister_tracepoints(struct tracepoint *tp, void *ignore)
> +{
> + if (!strcmp(tp->name, "console"))
> + tracepoint_probe_unregister(tp, probe_console, NULL);
> +}
> +
> +/*
> + * We only want to do tracepoints setup and teardown once, therefore we have to
> + * customize the init and exit functions and cannot rely on kunit_test_suite().
> + */
> +static int __init kcsan_test_init(void)
> +{
> + /*
> + * Because we want to be able to build the test as a module, we need to
> + * iterate through all known tracepoints, since the static registration
> + * won't work here.
> + */
> + for_each_kernel_tracepoint(register_tracepoints, NULL);
> + return __kunit_test_suites_init(kcsan_test_suites);
> +}
> +
> +static void kcsan_test_exit(void)
> +{
> + __kunit_test_suites_exit(kcsan_test_suites);
> + for_each_kernel_tracepoint(unregister_tracepoints, NULL);
> + tracepoint_synchronize_unregister();
> +}
> +
> +late_initcall(kcsan_test_init);
> +module_exit(kcsan_test_exit);
> +
> +MODULE_LICENSE("GPL v2");
> +MODULE_AUTHOR("Marco Elver <elver@...gle.com>");
> diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> index 689b6b81f272..ea28245c6c1d 100644
> --- a/lib/Kconfig.kcsan
> +++ b/lib/Kconfig.kcsan
> @@ -41,7 +41,28 @@ config KCSAN_SELFTEST
> bool "Perform short selftests on boot"
> default y
> help
> - Run KCSAN selftests on boot. On test failure, causes the kernel to panic.
> + Run KCSAN selftests on boot. On test failure, causes the kernel to
> + panic. Recommended to be enabled, ensuring critical functionality
> + works as intended.
> +
> +config KCSAN_TEST
> + tristate "KCSAN test for integrated runtime behaviour"
> + depends on TRACEPOINTS && KUNIT
> + select TORTURE_TEST
> + help
> + KCSAN test focusing on behaviour of the integrated runtime. Tests
> + various race scenarios, and verifies the reports generated to
> + console. Makes use of KUnit for test organization, and the Torture
> + framework for test thread control.
> +
> + Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS
> + milliseconds. Test run duration may be optimized by building the
> + kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower
> + than default value.
> +
> + Say Y here if you want the test to be built into the kernel and run
> + during boot; say M if you want the test to build as a module; say N
> + if you are unsure.
>
> config KCSAN_EARLY_ENABLE
> bool "Early enable during boot"
> --
> 2.26.2.526.g744177e7f7-goog
>
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