Commit 3021e692 authored by Andrey Konovalov's avatar Andrey Konovalov Committed by Linus Torvalds
Browse files

kcov: check kcov_softirq in kcov_remote_stop() 



kcov_remote_stop() should check that the corresponding kcov_remote_start()
actually found the specified remote handle and started collecting
coverage.  This is done by checking the per thread kcov_softirq flag.

A particular failure scenario where this was observed involved a softirq
with a remote coverage collection section coming between check_kcov_mode()
and the access to t->kcov_area in __sanitizer_cov_trace_pc().  In that
softirq kcov_remote_start() bailed out after kcov_remote_find() check, but
the matching kcov_remote_stop() didn't check if kcov_remote_start()
succeeded, and overwrote per thread kcov parameters with invalid (zero)
values.

Fixes: 5ff3b30a ("kcov: collect coverage from interrupts")
Signed-off-by: default avatarAndrey Konovalov <andreyknvl@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Link: http://lkml.kernel.org/r/fcd1cd16eac1d2c01a66befd8ea4afc6f8d09833.1591576806.git.andreyknvl@google.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 40590660

kernel/kcov.c

+18 −8
Original line number Diff line number Diff line
@@ -427,7 +427,8 @@ void kcov_task_exit(struct task_struct *t) 
	 *        WARN_ON(!kcov->remote && kcov->t != t);

	 *

	 * For KCOV_REMOTE_ENABLE devices, the exiting task is either:

	 * 2. A remote task between kcov_remote_start() and kcov_remote_stop().

	 *

	 * 1. A remote task between kcov_remote_start() and kcov_remote_stop().

	 *    In this case we should print a warning right away, since a task

	 *    shouldn't be exiting when it's in a kcov coverage collection

	 *    section. Here t points to the task that is collecting remote
@@ -437,7 +438,7 @@ void kcov_task_exit(struct task_struct *t) 
	 *        WARN_ON(kcov->remote && kcov->t != t);

	 *

	 * 2. The task that created kcov exiting without calling KCOV_DISABLE,

	 *    and then again we can make sure that t->kcov->t == t:

	 *    and then again we make sure that t->kcov->t == t:

	 *        WARN_ON(kcov->remote && kcov->t != t);

	 *

	 * By combining all three checks into one we get:
@@ -764,7 +765,7 @@ static const struct file_operations kcov_fops = { 
 * Internally, kcov_remote_start() looks up the kcov device associated with the

 * provided handle, allocates an area for coverage collection, and saves the

 * pointers to kcov and area into the current task_struct to allow coverage to

 * be collected via __sanitizer_cov_trace_pc()

 * be collected via __sanitizer_cov_trace_pc().

 * In turns kcov_remote_stop() clears those pointers from task_struct to stop

 * collecting coverage and copies all collected coverage into the kcov area.

 */
@@ -972,16 +973,25 @@ void kcov_remote_stop(void) 
		local_irq_restore(flags);

		return;

	}

	kcov = t->kcov;

	area = t->kcov_area;

	size = t->kcov_size;

	sequence = t->kcov_sequence;



	/*

	 * When in softirq, check if the corresponding kcov_remote_start()

	 * actually found the remote handle and started collecting coverage.

	 */

	if (in_serving_softirq() && !t->kcov_softirq) {

		local_irq_restore(flags);

		return;

	}

	/* Make sure that kcov_softirq is only set when in softirq. */

	if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {

		local_irq_restore(flags);

		return;

	}



	kcov = t->kcov;

	area = t->kcov_area;

	size = t->kcov_size;

	sequence = t->kcov_sequence;



	kcov_stop(t);

	if (in_serving_softirq()) {

		t->kcov_softirq = 0;

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