Commit ad4f8eec authored by Marco Elver's avatar Marco Elver Committed by Ingo Molnar
Browse files

kcsan: Address missing case with KCSAN_REPORT_VALUE_CHANGE_ONLY 



Even with KCSAN_REPORT_VALUE_CHANGE_ONLY, KCSAN still reports data
races between reads and watchpointed writes, even if the writes wrote
values already present.  This commit causes KCSAN to unconditionally
skip reporting in this case.

Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent f1bc9621

kernel/kcsan/report.c

+20 −7
Original line number Diff line number Diff line
@@ -130,12 +130,25 @@ static bool rate_limit_report(unsigned long frame1, unsigned long frame2) 
 * Special rules to skip reporting.

 */

static bool

skip_report(int access_type, bool value_change, unsigned long top_frame)

skip_report(bool value_change, unsigned long top_frame)

{

	const bool is_write = (access_type & KCSAN_ACCESS_WRITE) != 0;



	if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) && is_write &&

	    !value_change) {

	/*

	 * 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): impossible;

	 *

	 * 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; and

	 * case 6 is simply impossible.

	 */

	if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) && !value_change) {

		/*

		 * The access is a write, but the data value did not change.

		 *
@@ -228,7 +241,7 @@ 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(access_type, true, stack_entries[skipnr]))

	if (skip_report(true, stack_entries[skipnr]))

		return false;



	if (type == KCSAN_REPORT_RACE_SIGNAL) {
@@ -237,7 +250,7 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, 
		other_frame = other_info.stack_entries[other_skipnr];



		/* @value_change is only known for the other thread */

		if (skip_report(other_info.access_type, value_change, other_frame))

		if (skip_report(value_change, other_frame))

			return false;

	}