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kcov: Add interrupt handling self test

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Add a boot self test that can catch sprious coverage from interrupts.
The coverage callback filters out interrupt code, but only after the
handler updates preempt count. Some code periodically leaks out
of that section and leads to spurious coverage.
Add a best-effort (but simple) test that is likely to catch such bugs.
If the test is enabled on CI systems that use KCOV, they should catch
any issues fast.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://lore.kernel.org/all/7662127c97e29da1a748ad1c1539dd7b65b737b2.1718092070.git.dvyukov@google.com
This commit is contained in:
Dmitry Vyukov 2024-06-11 09:50:31 +02:00 committed by Thomas Gleixner
parent 477d81a1c4
commit 6cd0dd934b
2 changed files with 39 additions and 0 deletions
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31
kernel/kcov.c
View file

@ -11,6 +11,7 @@
#include <linux/fs.h>
#include <linux/hashtable.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/kmsan-checks.h>
#include <linux/mm.h>
#include <linux/preempt.h>
@ -1058,6 +1059,32 @@ u64 kcov_common_handle(void)
}
EXPORT_SYMBOL(kcov_common_handle);
#ifdef CONFIG_KCOV_SELFTEST
static void __init selftest(void)
{
unsigned long start;
pr_err("running self test\n");
/*
* Test that interrupts don't produce spurious coverage.
* The coverage callback filters out interrupt code, but only
* after the handler updates preempt count. Some code periodically
* leaks out of that section and leads to spurious coverage.
* It's hard to call the actual interrupt handler directly,
* so we just loop here for a bit waiting for a timer interrupt.
* We set kcov_mode to enable tracing, but don't setup the area,
* so any attempt to trace will crash. Note: we must not call any
* potentially traced functions in this region.
*/
start = jiffies;
current->kcov_mode = KCOV_MODE_TRACE_PC;
while ((jiffies - start) * MSEC_PER_SEC / HZ < 300)
;
current->kcov_mode = 0;
pr_err("done running self test\n");
}
#endif
static int __init kcov_init(void)
{
int cpu;
@ -1077,6 +1104,10 @@ static int __init kcov_init(void)
*/
debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops);
#ifdef CONFIG_KCOV_SELFTEST
selftest();
#endif
return 0;
}

8
lib/Kconfig.debug
View file

@ -2173,6 +2173,14 @@ config KCOV_IRQ_AREA_SIZE
soft interrupts. This specifies the size of those areas in the
number of unsigned long words.
config KCOV_SELFTEST
bool "Perform short selftests on boot"
depends on KCOV
help
Run short KCOV coverage collection selftests on boot.
On test failure, causes the kernel to panic. Recommended to be
enabled, ensuring critical functionality works as intended.
menuconfig RUNTIME_TESTING_MENU
bool "Runtime Testing"
default y