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kcsan: Introduce kcsan_value_change type

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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>
This commit is contained in:
Marco Elver
2020-02-11 17:04:21 +01:00
committed by Ingo Molnar
parent b968a08f24
commit b738f6169f
3 changed files with 54 additions and 29 deletions
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26
kernel/kcsan/report.c
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@@ -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;