Re: [PATCH 1/2] lkdtm/bugs: Add cases for BUG and PANIC occurring in hardirq context

[Kees Cook <kees@kernel.org>]

On Wed, Nov 12, 2025 at 06:53:18PM +0100, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
> 
> Add lkdtm cases to trigger a BUG() or panic() from hardirq context. This
> is useful for testing pstore behavior being invoked from such contexts.

Sorry I lost this! Thanks for the offline ping. :)

> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  drivers/misc/lkdtm/bugs.c | 53 ++++++++++++++++++++
>  1 file changed, 53 insertions(+)
> 
> diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
> index 376047beea3d..fa05d77acb55 100644
> --- a/drivers/misc/lkdtm/bugs.c
> +++ b/drivers/misc/lkdtm/bugs.c
> @@ -8,6 +8,7 @@
>  #include "lkdtm.h"
>  #include <linux/cpu.h>
>  #include <linux/list.h>
> +#include <linux/hrtimer.h>
>  #include <linux/sched.h>
>  #include <linux/sched/signal.h>
>  #include <linux/sched/task_stack.h>
> @@ -100,11 +101,61 @@ static void lkdtm_PANIC_STOP_IRQOFF(void)
>  	stop_machine(panic_stop_irqoff_fn, &v, cpu_online_mask);
>  }
>  
> +static bool wait_for_panic;
> +
> +static enum hrtimer_restart panic_in_hardirq(struct hrtimer *timer)
> +{
> +	panic("from hard IRQ context");
> +
> +	wait_for_panic = false;
> +	return HRTIMER_NORESTART;
> +}
> +
> +static void lkdtm_PANIC_IN_HARDIRQ(void)
> +{
> +	struct hrtimer timer;
> +
> +	wait_for_panic = true;
> +	hrtimer_setup_on_stack(&timer, panic_in_hardirq,
> +			       CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
> +	hrtimer_start(&timer, us_to_ktime(100), HRTIMER_MODE_REL_HARD);
> +
> +	while (wait_for_panic)
> +		;
> +
> +	hrtimer_cancel(&timer);
> +}
> +
>  static void lkdtm_BUG(void)
>  {
>  	BUG();
>  }
>  
> +static bool wait_for_bug;
> +
> +static enum hrtimer_restart bug_in_hardirq(struct hrtimer *timer)
> +{
> +	BUG();
> +
> +	wait_for_bug = false;
> +	return HRTIMER_NORESTART;
> +}
> +
> +static void lkdtm_BUG_IN_HARDIRQ(void)
> +{
> +	struct hrtimer timer;
> +
> +	wait_for_bug = true;
> +	hrtimer_setup_on_stack(&timer, bug_in_hardirq,
> +			       CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
> +	hrtimer_start(&timer, us_to_ktime(100), HRTIMER_MODE_REL_HARD);
> +
> +	while (wait_for_bug)
> +		;
> +
> +	hrtimer_cancel(&timer);
> +}
> +
>  static int warn_counter;
>  
>  static void lkdtm_WARNING(void)
> @@ -696,7 +747,9 @@ static noinline void lkdtm_CORRUPT_PAC(void)
>  static struct crashtype crashtypes[] = {
>  	CRASHTYPE(PANIC),
>  	CRASHTYPE(PANIC_STOP_IRQOFF),
> +	CRASHTYPE(PANIC_IN_HARDIRQ),
>  	CRASHTYPE(BUG),
> +	CRASHTYPE(BUG_IN_HARDIRQ),
>  	CRASHTYPE(WARNING),
>  	CRASHTYPE(WARNING_MESSAGE),
>  	CRASHTYPE(EXCEPTION),

This all looks good to me. I always ask that new tests also get added to
the lkdtm selftest runner list in tools/testing/selftests/lkdtm/tests.txt

IIUC, bug in hardirq will result in a panic, so both these tests will
take out the entire system, so they should be skipped for the selftest.
Perhaps:


diff --git a/tools/testing/selftests/lkdtm/tests.txt b/tools/testing/selftests/lkdtm/tests.txt
index cff124c1eddd..67cd53715d93 100644
--- a/tools/testing/selftests/lkdtm/tests.txt
+++ b/tools/testing/selftests/lkdtm/tests.txt
@@ -1,6 +1,8 @@
 #PANIC
 #PANIC_STOP_IRQOFF Crashes entire system
+#PANIC_IN_HARDIRQ Crashes entire system
 BUG kernel BUG at
+#BUG_IN_HARDIRQ Crashes entire system
 WARNING WARNING:
 WARNING_MESSAGE message trigger
 EXCEPTION




-- 
Kees Cook