Re: [PATCH] kasan: support panic_on_warn

[Andrey Ryabinin]

On 10/14/2016 08:10 PM, Dmitry Vyukov wrote:
> If user sets panic_on_warn, he wants kernel to panic if there is
> anything barely wrong with the kernel. KASAN-detected errors
> are definitely not less benign than an arbitrary kernel WARNING.
> 
> Panic after KASAN errors if panic_on_warn is set.
> 
> We use this for continuous fuzzing where we want kernel to stop
> and reboot on any error.
> 
> Signed-off-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: kasan-dev@xxxxxxxxxxxxxxxx
> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
>  mm/kasan/report.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 24c1211..ca0bd48 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -133,6 +133,10 @@ static void kasan_end_report(unsigned long *flags)
>  	pr_err("==================================================================\n");
>  	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
>  	spin_unlock_irqrestore(&report_lock, *flags);
> +	if (panic_on_warn) {
> +		panic_on_warn = 0;

Why we need to reset panic_on_warn?
I assume this was copied from __warn(). AFAIU in __warn() this protects from recursion:
 __warn() -> painc() ->__warn() -> panic() -> ...
which is possible if WARN_ON() triggered in panic().
But KASAN is protected from such recursion via kasan_disable_current().

> +		panic("panic_on_warn set ...\n");
> +	}
>  	kasan_enable_current();
>  }
>  
>