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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: 5ff3b30ab5 ("kcov: collect coverage from interrupts")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Dmitry 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: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrey Konovalov 2020-06-10 18:41:28 -07:00 committed by Linus Torvalds
parent 405906600a
commit 3021e69219
1 changed files with 18 additions and 8 deletions
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26
kernel/kcov.c
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@ -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;