kcsan: Introduce kcsan_value_change type
Introduces kcsan_value_change type, which explicitly points out if we either observed a value-change (TRUE), or we could not observe one but cannot rule out a value-change happened (MAYBE). The MAYBE state can either be reported or not, depending on configuration preferences. A follow-up patch introduces the FALSE state, which should never be reported. No functional change intended. Acked-by: John Hubbard <jhubbard@nvidia.com> Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -341,7 +341,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
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u32 _4;
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u64 _8;
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} expect_value;
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bool value_change = false;
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enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE;
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unsigned long ua_flags = user_access_save();
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unsigned long irq_flags;
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@ -398,6 +398,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
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* Read the current value, to later check and infer a race if the data
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* was modified via a non-instrumented access, e.g. from a device.
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*/
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expect_value._8 = 0;
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switch (size) {
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case 1:
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expect_value._1 = READ_ONCE(*(const u8 *)ptr);
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@ -436,23 +437,36 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
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*/
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switch (size) {
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case 1:
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value_change = expect_value._1 != READ_ONCE(*(const u8 *)ptr);
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expect_value._1 ^= READ_ONCE(*(const u8 *)ptr);
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break;
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case 2:
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value_change = expect_value._2 != READ_ONCE(*(const u16 *)ptr);
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expect_value._2 ^= READ_ONCE(*(const u16 *)ptr);
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break;
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case 4:
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value_change = expect_value._4 != READ_ONCE(*(const u32 *)ptr);
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expect_value._4 ^= READ_ONCE(*(const u32 *)ptr);
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break;
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case 8:
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value_change = expect_value._8 != READ_ONCE(*(const u64 *)ptr);
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expect_value._8 ^= READ_ONCE(*(const u64 *)ptr);
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break;
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default:
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break; /* ignore; we do not diff the values */
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}
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/* Were we able to observe a value-change? */
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if (expect_value._8 != 0)
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value_change = KCSAN_VALUE_CHANGE_TRUE;
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/* Check if this access raced with another. */
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if (!remove_watchpoint(watchpoint)) {
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/*
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* Depending on the access type, map a value_change of MAYBE to
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* TRUE (require reporting).
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*/
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if (value_change == KCSAN_VALUE_CHANGE_MAYBE && (size > 8 || is_assert)) {
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/* Always assume a value-change. */
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value_change = KCSAN_VALUE_CHANGE_TRUE;
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}
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/*
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* No need to increment 'data_races' counter, as the racing
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* thread already did.
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@ -461,20 +475,12 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
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* therefore both this thread and the racing thread may
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* increment this counter.
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*/
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if (is_assert)
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if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)
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kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);
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/*
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* - If we were not able to observe a value change due to size
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* constraints, always assume a value change.
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* - If the access type is an assertion, we also always assume a
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* value change to always report the race.
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*/
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value_change = value_change || size > 8 || is_assert;
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kcsan_report(ptr, size, type, value_change, smp_processor_id(),
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KCSAN_REPORT_RACE_SIGNAL);
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} else if (value_change) {
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} else if (value_change == KCSAN_VALUE_CHANGE_TRUE) {
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/* Inferring a race, since the value should not have changed. */
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kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN);
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@ -482,7 +488,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
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kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);
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if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert)
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kcsan_report(ptr, size, type, true,
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kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE,
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smp_processor_id(),
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KCSAN_REPORT_RACE_UNKNOWN_ORIGIN);
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}
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@ -88,6 +88,22 @@ extern void kcsan_counter_dec(enum kcsan_counter_id id);
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*/
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extern bool kcsan_skip_report_debugfs(unsigned long func_addr);
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/*
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* Value-change states.
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*/
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enum kcsan_value_change {
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/*
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* Did not observe a value-change, however, it is valid to report the
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* race, depending on preferences.
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*/
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KCSAN_VALUE_CHANGE_MAYBE,
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/*
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* The value was observed to change, and the race should be reported.
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*/
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KCSAN_VALUE_CHANGE_TRUE,
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};
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enum kcsan_report_type {
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/*
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* The thread that set up the watchpoint and briefly stalled was
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@ -111,6 +127,7 @@ enum kcsan_report_type {
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* Print a race report from thread that encountered the race.
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*/
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extern void kcsan_report(const volatile void *ptr, size_t size, int access_type,
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bool value_change, int cpu_id, enum kcsan_report_type type);
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enum kcsan_value_change value_change, int cpu_id,
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enum kcsan_report_type type);
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#endif /* _KERNEL_KCSAN_KCSAN_H */
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@ -130,26 +130,27 @@ static bool rate_limit_report(unsigned long frame1, unsigned long frame2)
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* Special rules to skip reporting.
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*/
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static bool
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skip_report(bool value_change, unsigned long top_frame)
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skip_report(enum kcsan_value_change value_change, unsigned long top_frame)
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{
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/*
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* The first call to skip_report always has value_change==true, since we
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* The first call to skip_report always has value_change==TRUE, since we
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* cannot know the value written of an instrumented access. For the 2nd
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* call there are 6 cases with CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY:
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*
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* 1. read watchpoint, conflicting write (value_change==true): report;
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* 2. read watchpoint, conflicting write (value_change==false): skip;
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* 3. write watchpoint, conflicting write (value_change==true): report;
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* 4. write watchpoint, conflicting write (value_change==false): skip;
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* 5. write watchpoint, conflicting read (value_change==false): skip;
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* 6. write watchpoint, conflicting read (value_change==true): report;
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* 1. read watchpoint, conflicting write (value_change==TRUE): report;
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* 2. read watchpoint, conflicting write (value_change==MAYBE): skip;
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* 3. write watchpoint, conflicting write (value_change==TRUE): report;
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* 4. write watchpoint, conflicting write (value_change==MAYBE): skip;
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* 5. write watchpoint, conflicting read (value_change==MAYBE): skip;
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* 6. write watchpoint, conflicting read (value_change==TRUE): report;
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*
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* Cases 1-4 are intuitive and expected; case 5 ensures we do not report
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* data races where the write may have rewritten the same value; case 6
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* is possible either if the size is larger than what we check value
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* changes for or the access type is KCSAN_ACCESS_ASSERT.
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*/
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if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) && !value_change) {
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if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) &&
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value_change == KCSAN_VALUE_CHANGE_MAYBE) {
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/*
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* The access is a write, but the data value did not change.
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*
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@ -245,7 +246,7 @@ static int sym_strcmp(void *addr1, void *addr2)
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* Returns true if a report was generated, false otherwise.
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*/
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static bool print_report(const volatile void *ptr, size_t size, int access_type,
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bool value_change, int cpu_id,
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enum kcsan_value_change value_change, int cpu_id,
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enum kcsan_report_type type)
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{
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unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 };
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@ -258,7 +259,7 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
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/*
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* Must check report filter rules before starting to print.
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*/
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if (skip_report(true, stack_entries[skipnr]))
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if (skip_report(KCSAN_VALUE_CHANGE_TRUE, stack_entries[skipnr]))
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return false;
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if (type == KCSAN_REPORT_RACE_SIGNAL) {
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@ -477,7 +478,8 @@ retry:
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}
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void kcsan_report(const volatile void *ptr, size_t size, int access_type,
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bool value_change, int cpu_id, enum kcsan_report_type type)
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enum kcsan_value_change value_change, int cpu_id,
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enum kcsan_report_type type)
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{
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unsigned long flags = 0;
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