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>

1 files changed, 14 insertions, 12 deletions

diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index abf6852dff72..d871476dc134 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -130,26 +130,27 @@ static bool rate_limit_report(unsigned long frame1, unsigned long frame2)
  * Special rules to skip reporting.
  */
 static bool
-skip_report(bool value_change, unsigned long top_frame)
+skip_report(enum kcsan_value_change value_change, unsigned long top_frame)
 {
 	/*
-	 * The first call to skip_report always has value_change==true, since we
+	 * The first call to skip_report always has value_change==TRUE, since we
 	 * cannot know the value written of an instrumented access. For the 2nd
 	 * call there are 6 cases with CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY:
 	 *
-	 * 1. read watchpoint, conflicting write (value_change==true): report;
-	 * 2. read watchpoint, conflicting write (value_change==false): skip;
-	 * 3. write watchpoint, conflicting write (value_change==true): report;
-	 * 4. write watchpoint, conflicting write (value_change==false): skip;
-	 * 5. write watchpoint, conflicting read (value_change==false): skip;
-	 * 6. write watchpoint, conflicting read (value_change==true): report;
+	 * 1. read watchpoint, conflicting write (value_change==TRUE): report;
+	 * 2. read watchpoint, conflicting write (value_change==MAYBE): skip;
+	 * 3. write watchpoint, conflicting write (value_change==TRUE): report;
+	 * 4. write watchpoint, conflicting write (value_change==MAYBE): skip;
+	 * 5. write watchpoint, conflicting read (value_change==MAYBE): skip;
+	 * 6. write watchpoint, conflicting read (value_change==TRUE): report;
 	 *
 	 * Cases 1-4 are intuitive and expected; case 5 ensures we do not report
 	 * data races where the write may have rewritten the same value; case 6
 	 * is possible either if the size is larger than what we check value
 	 * changes for or the access type is KCSAN_ACCESS_ASSERT.
 	 */
-	if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) && !value_change) {
+	if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) &&
+	    value_change == KCSAN_VALUE_CHANGE_MAYBE) {
 		/*
 		 * The access is a write, but the data value did not change.
 		 *
@@ -245,7 +246,7 @@ static int sym_strcmp(void *addr1, void *addr2)
  * Returns true if a report was generated, false otherwise.
  */
 static bool print_report(const volatile void *ptr, size_t size, int access_type,
-			 bool value_change, int cpu_id,
+			 enum kcsan_value_change value_change, int cpu_id,
 			 enum kcsan_report_type type)
 {
 	unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 };
@@ -258,7 +259,7 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
 	/*
 	 * Must check report filter rules before starting to print.
 	 */
-	if (skip_report(true, stack_entries[skipnr]))
+	if (skip_report(KCSAN_VALUE_CHANGE_TRUE, stack_entries[skipnr]))
 		return false;
 
 	if (type == KCSAN_REPORT_RACE_SIGNAL) {
@@ -477,7 +478,8 @@ retry:
 }
 
 void kcsan_report(const volatile void *ptr, size_t size, int access_type,
-		  bool value_change, int cpu_id, enum kcsan_report_type type)
+		  enum kcsan_value_change value_change, int cpu_id,
+		  enum kcsan_report_type type)
 {
 	unsigned long flags = 0;