linux-kernel - Re: [PATCH] kasan: support panic_on

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Date:   Mon, 17 Oct 2016 10:18:11 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kasan: support panic_on_warn

On Mon, Oct 17, 2016 at 10:13 AM, Andrey Ryabinin
<aryabinin@...tuozzo.com> wrote:
>
>
> 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@...gle.com>
>> Cc: kasan-dev@...glegroups.com
>> Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
>> Cc: Alexander Potapenko <glider@...gle.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: linux-mm@...ck.org
>> Cc: linux-kernel@...r.kernel.org
>> ---
>>  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().

But we have recursion into panic via kasan->panic->warning->panic. Am
I missing something?


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