From b738f6169f1260b4ed5bd9f220b1c84d79f3ab8d Mon Sep 17 00:00:00 2001 From: Marco Elver Date: Tue, 11 Feb 2020 17:04:21 +0100 Subject: 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 Signed-off-by: Marco Elver Signed-off-by: Paul E. McKenney Signed-off-by: Ingo Molnar --- kernel/kcsan/core.c | 38 ++++++++++++++++++++++---------------- 1 file changed, 22 insertions(+), 16 deletions(-) (limited to 'kernel/kcsan/core.c') diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index 498b1eb3c1cd..3f89801161d3 100644 --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -341,7 +341,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) u32 _4; u64 _8; } expect_value; - bool value_change = false; + enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE; unsigned long ua_flags = user_access_save(); unsigned long irq_flags; @@ -398,6 +398,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) * Read the current value, to later check and infer a race if the data * was modified via a non-instrumented access, e.g. from a device. */ + expect_value._8 = 0; switch (size) { case 1: expect_value._1 = READ_ONCE(*(const u8 *)ptr); @@ -436,23 +437,36 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) */ switch (size) { case 1: - value_change = expect_value._1 != READ_ONCE(*(const u8 *)ptr); + expect_value._1 ^= READ_ONCE(*(const u8 *)ptr); break; case 2: - value_change = expect_value._2 != READ_ONCE(*(const u16 *)ptr); + expect_value._2 ^= READ_ONCE(*(const u16 *)ptr); break; case 4: - value_change = expect_value._4 != READ_ONCE(*(const u32 *)ptr); + expect_value._4 ^= READ_ONCE(*(const u32 *)ptr); break; case 8: - value_change = expect_value._8 != READ_ONCE(*(const u64 *)ptr); + expect_value._8 ^= READ_ONCE(*(const u64 *)ptr); break; default: break; /* ignore; we do not diff the values */ } + /* Were we able to observe a value-change? */ + if (expect_value._8 != 0) + value_change = KCSAN_VALUE_CHANGE_TRUE; + /* Check if this access raced with another. */ if (!remove_watchpoint(watchpoint)) { + /* + * Depending on the access type, map a value_change of MAYBE to + * TRUE (require reporting). + */ + if (value_change == KCSAN_VALUE_CHANGE_MAYBE && (size > 8 || is_assert)) { + /* Always assume a value-change. */ + value_change = KCSAN_VALUE_CHANGE_TRUE; + } + /* * No need to increment 'data_races' counter, as the racing * thread already did. @@ -461,20 +475,12 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) * therefore both this thread and the racing thread may * increment this counter. */ - if (is_assert) + if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE) kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES); - /* - * - If we were not able to observe a value change due to size - * constraints, always assume a value change. - * - If the access type is an assertion, we also always assume a - * value change to always report the race. - */ - value_change = value_change || size > 8 || is_assert; - kcsan_report(ptr, size, type, value_change, smp_processor_id(), KCSAN_REPORT_RACE_SIGNAL); - } else if (value_change) { + } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) { /* Inferring a race, since the value should not have changed. */ kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN); @@ -482,7 +488,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES); if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert) - kcsan_report(ptr, size, type, true, + kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE, smp_processor_id(), KCSAN_REPORT_RACE_UNKNOWN_ORIGIN); } -- cgit v1.2.3