Commit 135c0872 authored by Marco Elver's avatar Marco Elver Committed by Paul E. McKenney
Browse files

kcsan: Introduce report access_info and other_info 



Improve readability by introducing access_info and other_info structs,
and in preparation of the following commit in this series replaces the
single instance of other_info with an array of size 1.

No functional change intended.

Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 1443b8c9

kernel/kcsan/core.c

+2 −4
Original line number Diff line number Diff line
@@ -321,7 +321,7 @@ static noinline void kcsan_found_watchpoint(const volatile void *ptr, 
	flags = user_access_save();



	if (consumed) {

		kcsan_report(ptr, size, type, true, raw_smp_processor_id(),

		kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE,

			     KCSAN_REPORT_CONSUMED_WATCHPOINT);

	} else {

		/*
@@ -500,8 +500,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 
		if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)

			kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);



		kcsan_report(ptr, size, type, value_change, raw_smp_processor_id(),

			     KCSAN_REPORT_RACE_SIGNAL);

		kcsan_report(ptr, size, type, value_change, KCSAN_REPORT_RACE_SIGNAL);

	} else if (value_change == KCSAN_VALUE_CHANGE_TRUE) {

		/* Inferring a race, since the value should not have changed. */
@@ -511,7 +510,6 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 


		if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert)

			kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE,

				     raw_smp_processor_id(),

				     KCSAN_REPORT_RACE_UNKNOWN_ORIGIN);

	}

kernel/kcsan/kcsan.h

+1 −1
Original line number Diff line number Diff line
@@ -135,7 +135,7 @@ enum kcsan_report_type { 
 * Print a race report from thread that encountered the race.

 */

extern void kcsan_report(const volatile void *ptr, size_t size, int access_type,

			 enum kcsan_value_change value_change, int cpu_id,

			 enum kcsan_value_change value_change,

			 enum kcsan_report_type type);



#endif /* _KERNEL_KCSAN_KCSAN_H */

kernel/kcsan/report.c

+74 −73
Original line number Diff line number Diff line
@@ -19,18 +19,23 @@ 
 */

#define NUM_STACK_ENTRIES 64



/* Common access info. */

struct access_info {

	const volatile void	*ptr;

	size_t			size;

	int			access_type;

	int			task_pid;

	int			cpu_id;

};



/*

 * Other thread info: communicated from other racing thread to thread that set

 * up the watchpoint, which then prints the complete report atomically. Only

 * need one struct, as all threads should to be serialized regardless to print

 * the reports, with reporting being in the slow-path.

 */

static struct {

	const volatile void	*ptr;

	size_t			size;

	int			access_type;

	int			task_pid;

	int			cpu_id;

struct other_info {

	struct access_info	ai;

	unsigned long		stack_entries[NUM_STACK_ENTRIES];

	int			num_stack_entries;
@@ -52,7 +57,9 @@ static struct { 
	 * that populated @other_info until it has been consumed.

	 */

	struct task_struct	*task;

} other_info;

};



static struct other_info other_infos[1];



/*

 * Information about reported races; used to rate limit reporting.
@@ -238,7 +245,7 @@ static const char *get_thread_desc(int task_id) 
}



/* Helper to skip KCSAN-related functions in stack-trace. */

static int get_stack_skipnr(unsigned long stack_entries[], int num_entries)

static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries)

{

	char buf[64];

	int skip = 0;
@@ -279,9 +286,10 @@ static void print_verbose_info(struct task_struct *task) 
/*

 * Returns true if a report was generated, false otherwise.

 */

static bool print_report(const volatile void *ptr, size_t size, int access_type,

			 enum kcsan_value_change value_change, int cpu_id,

			 enum kcsan_report_type type)

static bool print_report(enum kcsan_value_change value_change,

			 enum kcsan_report_type type,

			 const struct access_info *ai,

			 const struct other_info *other_info)

{

	unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 };

	int num_stack_entries = stack_trace_save(stack_entries, NUM_STACK_ENTRIES, 1);
@@ -297,9 +305,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, 
		return false;



	if (type == KCSAN_REPORT_RACE_SIGNAL) {

		other_skipnr = get_stack_skipnr(other_info.stack_entries,

						other_info.num_stack_entries);

		other_frame = other_info.stack_entries[other_skipnr];

		other_skipnr = get_stack_skipnr(other_info->stack_entries,

						other_info->num_stack_entries);

		other_frame = other_info->stack_entries[other_skipnr];



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

		if (skip_report(value_change, other_frame))
@@ -321,13 +329,13 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, 
		 */

		cmp = sym_strcmp((void *)other_frame, (void *)this_frame);

		pr_err("BUG: KCSAN: %s in %ps / %ps\n",

		       get_bug_type(access_type | other_info.access_type),

		       get_bug_type(ai->access_type | other_info->ai.access_type),

		       (void *)(cmp < 0 ? other_frame : this_frame),

		       (void *)(cmp < 0 ? this_frame : other_frame));

	} break;



	case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN:

		pr_err("BUG: KCSAN: %s in %pS\n", get_bug_type(access_type),

		pr_err("BUG: KCSAN: %s in %pS\n", get_bug_type(ai->access_type),

		       (void *)this_frame);

		break;
@@ -341,30 +349,28 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, 
	switch (type) {

	case KCSAN_REPORT_RACE_SIGNAL:

		pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",

		       get_access_type(other_info.access_type), other_info.ptr,

		       other_info.size, get_thread_desc(other_info.task_pid),

		       other_info.cpu_id);

		       get_access_type(other_info->ai.access_type), other_info->ai.ptr,

		       other_info->ai.size, get_thread_desc(other_info->ai.task_pid),

		       other_info->ai.cpu_id);



		/* Print the other thread's stack trace. */

		stack_trace_print(other_info.stack_entries + other_skipnr,

				  other_info.num_stack_entries - other_skipnr,

		stack_trace_print(other_info->stack_entries + other_skipnr,

				  other_info->num_stack_entries - other_skipnr,

				  0);



		if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))

			print_verbose_info(other_info.task);

			print_verbose_info(other_info->task);



		pr_err("\n");

		pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",

		       get_access_type(access_type), ptr, size,

		       get_thread_desc(in_task() ? task_pid_nr(current) : -1),

		       cpu_id);

		       get_access_type(ai->access_type), ai->ptr, ai->size,

		       get_thread_desc(ai->task_pid), ai->cpu_id);

		break;



	case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN:

		pr_err("race at unknown origin, with %s to 0x%px of %zu bytes by %s on cpu %i:\n",

		       get_access_type(access_type), ptr, size,

		       get_thread_desc(in_task() ? task_pid_nr(current) : -1),

		       cpu_id);

		       get_access_type(ai->access_type), ai->ptr, ai->size,

		       get_thread_desc(ai->task_pid), ai->cpu_id);

		break;



	default:
@@ -386,22 +392,23 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type, 
	return true;

}



static void release_report(unsigned long *flags, enum kcsan_report_type type)

static void release_report(unsigned long *flags, struct other_info *other_info)

{

	if (type == KCSAN_REPORT_RACE_SIGNAL)

		other_info.ptr = NULL; /* mark for reuse */

	if (other_info)

		other_info->ai.ptr = NULL; /* Mark for reuse. */



	spin_unlock_irqrestore(&report_lock, *flags);

}



/*

 * Sets @other_info.task and awaits consumption of @other_info.

 * Sets @other_info->task and awaits consumption of @other_info.

 *

 * Precondition: report_lock is held.

 * Postcondition: report_lock is held.

 */

static void

set_other_info_task_blocking(unsigned long *flags, const volatile void *ptr)

static void set_other_info_task_blocking(unsigned long *flags,

					 const struct access_info *ai,

					 struct other_info *other_info)

{

	/*

	 * We may be instrumenting a code-path where current->state is already
@@ -418,7 +425,7 @@ set_other_info_task_blocking(unsigned long *flags, const volatile void *ptr) 
	 */

	int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt);



	other_info.task = current;

	other_info->task = current;

	do {

		if (is_running) {

			/*
@@ -438,19 +445,19 @@ set_other_info_task_blocking(unsigned long *flags, const volatile void *ptr) 
		spin_lock_irqsave(&report_lock, *flags);

		if (timeout-- < 0) {

			/*

			 * Abort. Reset other_info.task to NULL, since it

			 * Abort. Reset @other_info->task to NULL, since it

			 * appears the other thread is still going to consume

			 * it. It will result in no verbose info printed for

			 * this task.

			 */

			other_info.task = NULL;

			other_info->task = NULL;

			break;

		}

		/*

		 * If @ptr nor @current matches, then our information has been

		 * consumed and we may continue. If not, retry.

		 */

	} while (other_info.ptr == ptr && other_info.task == current);

	} while (other_info->ai.ptr == ai->ptr && other_info->task == current);

	if (is_running)

		set_current_state(TASK_RUNNING);

}
@@ -460,9 +467,8 @@ set_other_info_task_blocking(unsigned long *flags, const volatile void *ptr) 
 * acquires the matching other_info and returns true. If other_info is not

 * required for the report type, simply acquires report_lock and returns true.

 */

static bool prepare_report(unsigned long *flags, const volatile void *ptr,

			   size_t size, int access_type, int cpu_id,

			   enum kcsan_report_type type)

static bool prepare_report(unsigned long *flags, enum kcsan_report_type type,

			   const struct access_info *ai, struct other_info *other_info)

{

	if (type != KCSAN_REPORT_CONSUMED_WATCHPOINT &&

	    type != KCSAN_REPORT_RACE_SIGNAL) {
@@ -476,18 +482,14 @@ retry: 


	switch (type) {

	case KCSAN_REPORT_CONSUMED_WATCHPOINT:

		if (other_info.ptr != NULL)

		if (other_info->ai.ptr)

			break; /* still in use, retry */



		other_info.ptr			= ptr;

		other_info.size			= size;

		other_info.access_type		= access_type;

		other_info.task_pid		= in_task() ? task_pid_nr(current) : -1;

		other_info.cpu_id		= cpu_id;

		other_info.num_stack_entries	= stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1);

		other_info->ai = *ai;

		other_info->num_stack_entries = stack_trace_save(other_info->stack_entries, NUM_STACK_ENTRIES, 1);



		if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))

			set_other_info_task_blocking(flags, ptr);

			set_other_info_task_blocking(flags, ai, other_info);



		spin_unlock_irqrestore(&report_lock, *flags);
@@ -498,37 +500,31 @@ retry: 
		return false;



	case KCSAN_REPORT_RACE_SIGNAL:

		if (other_info.ptr == NULL)

		if (!other_info->ai.ptr)

			break; /* no data available yet, retry */



		/*

		 * First check if this is the other_info we are expecting, i.e.

		 * matches based on how watchpoint was encoded.

		 */

		if (!matching_access((unsigned long)other_info.ptr &

					     WATCHPOINT_ADDR_MASK,

				     other_info.size,

				     (unsigned long)ptr & WATCHPOINT_ADDR_MASK,

				     size))

		if (!matching_access((unsigned long)other_info->ai.ptr & WATCHPOINT_ADDR_MASK, other_info->ai.size,

				     (unsigned long)ai->ptr & WATCHPOINT_ADDR_MASK, ai->size))

			break; /* mismatching watchpoint, retry */



		if (!matching_access((unsigned long)other_info.ptr,

				     other_info.size, (unsigned long)ptr,

				     size)) {

		if (!matching_access((unsigned long)other_info->ai.ptr, other_info->ai.size,

				     (unsigned long)ai->ptr, ai->size)) {

			/*

			 * If the actual accesses to not match, this was a false

			 * positive due to watchpoint encoding.

			 */

			kcsan_counter_inc(

				KCSAN_COUNTER_ENCODING_FALSE_POSITIVES);

			kcsan_counter_inc(KCSAN_COUNTER_ENCODING_FALSE_POSITIVES);



			/* discard this other_info */

			release_report(flags, KCSAN_REPORT_RACE_SIGNAL);

			release_report(flags, other_info);

			return false;

		}



		access_type |= other_info.access_type;

		if ((access_type & KCSAN_ACCESS_WRITE) == 0) {

		if (!((ai->access_type | other_info->ai.access_type) & KCSAN_ACCESS_WRITE)) {

			/*

			 * While the address matches, this is not the other_info

			 * from the thread that consumed our watchpoint, since
@@ -561,15 +557,11 @@ retry: 
			 * data, and at this point the likelihood that we

			 * re-report the same race again is high.

			 */

			release_report(flags, KCSAN_REPORT_RACE_SIGNAL);

			release_report(flags, other_info);

			return false;

		}



		/*

		 * Matching & usable access in other_info: keep other_info_lock

		 * locked, as this thread consumes it to print the full report;

		 * unlocked in release_report.

		 */

		/* Matching access in other_info. */

		return true;



	default:
@@ -582,10 +574,19 @@ retry: 
}



void kcsan_report(const volatile void *ptr, size_t size, int access_type,

		  enum kcsan_value_change value_change, int cpu_id,

		  enum kcsan_value_change value_change,

		  enum kcsan_report_type type)

{

	unsigned long flags = 0;

	const struct access_info ai = {

		.ptr		= ptr,

		.size		= size,

		.access_type	= access_type,

		.task_pid	= in_task() ? task_pid_nr(current) : -1,

		.cpu_id		= raw_smp_processor_id()

	};

	struct other_info *other_info = type == KCSAN_REPORT_RACE_UNKNOWN_ORIGIN

					? NULL : &other_infos[0];



	/*

	 * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if
@@ -596,19 +597,19 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type, 
	lockdep_off();



	kcsan_disable_current();

	if (prepare_report(&flags, ptr, size, access_type, cpu_id, type)) {

	if (prepare_report(&flags, type, &ai, other_info)) {

		/*

		 * Never report if value_change is FALSE, only if we it is

		 * either TRUE or MAYBE. In case of MAYBE, further filtering may

		 * be done once we know the full stack trace in print_report().

		 */

		bool reported = value_change != KCSAN_VALUE_CHANGE_FALSE &&

				print_report(ptr, size, access_type, value_change, cpu_id, type);

				print_report(value_change, type, &ai, other_info);



		if (reported && panic_on_warn)

			panic("panic_on_warn set ...\n");



		release_report(&flags, type);

		release_report(&flags, other_info);

	}

	kcsan_enable_current();

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