[PATCH] kasan: support panic_on_warn

[PATCH] kasan: support panic_on_warn

[Dmitry Vyukov]

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@google.com>
Cc: kasan-dev@googlegroups.com
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.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;
+		panic("panic_on_warn set ...\n");
+	}
 	kasan_enable_current();
 }
 
-- 
2.8.0.rc3.226.g39d4020

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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@google.com>
> Cc: kasan-dev@googlegroups.com
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.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().

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

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Re: [PATCH] kasan: support panic_on_warn

[Dmitry Vyukov]

On Mon, Oct 17, 2016 at 10:13 AM, Andrey Ryabinin
<aryabinin@virtuozzo.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@google.com>
>> Cc: kasan-dev@googlegroups.com
>> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
>> Cc: Alexander Potapenko <glider@google.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: linux-mm@kvack.org
>> Cc: linux-kernel@vger.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();
>>  }

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Re: [PATCH] kasan: support panic_on_warn

[Andrey Ryabinin]

On 10/17/2016 11:18 AM, Dmitry Vyukov wrote:
> On Mon, Oct 17, 2016 at 10:13 AM, Andrey Ryabinin
> <aryabinin@virtuozzo.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@google.com>
>>> Cc: kasan-dev@googlegroups.com
>>> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
>>> Cc: Alexander Potapenko <glider@google.com>
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Cc: linux-mm@kvack.org
>>> Cc: linux-kernel@vger.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.

We do, like almost every other panic() call in the kernel. But at least it's finite.
So, if finite recursion is a problem for panic() it should be fixed in panic(), rather then on every panic() call site.




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

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[PATCH] kasan: support panic_on_warn

[Dmitry Vyukov]

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@google.com>
Cc: kasan-dev@googlegroups.com
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org

---

Changes from v1:
 - don't reset panic_on_warn before calling panic()
---
 mm/kasan/report.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 24c1211..0ee8211 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -133,6 +133,8 @@ 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("panic_on_warn set ...\n");
 	kasan_enable_current();
 }
 
-- 
2.8.0.rc3.226.g39d4020

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Re: [PATCH] kasan: support panic_on_warn

[Andrey Ryabinin]

On 10/17/2016 11:57 AM, 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@google.com>
> Cc: kasan-dev@googlegroups.com
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> 

Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> ---
> 
> Changes from v1:
>  - don't reset panic_on_warn before calling panic()
> ---
>  mm/kasan/report.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 24c1211..0ee8211 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -133,6 +133,8 @@ 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("panic_on_warn set ...\n");
>  	kasan_enable_current();
>  }
>  
> 

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Re: [PATCH] kasan: support panic_on_warn

[Dmitry Vyukov]

On Mon, Oct 17, 2016 at 10:39 AM, Andrey Ryabinin
<aryabinin@virtuozzo.com> wrote:
>
>
> On 10/17/2016 11:18 AM, Dmitry Vyukov wrote:
>> On Mon, Oct 17, 2016 at 10:13 AM, Andrey Ryabinin
>> <aryabinin@virtuozzo.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@google.com>
>>>> Cc: kasan-dev@googlegroups.com
>>>> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
>>>> Cc: Alexander Potapenko <glider@google.com>
>>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>>> Cc: linux-mm@kvack.org
>>>> Cc: linux-kernel@vger.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.
>
> We do, like almost every other panic() call in the kernel. But at least it's finite.
> So, if finite recursion is a problem for panic() it should be fixed in panic(), rather then on every panic() call site.


I misunderstood the comment in warning code:

502                 /*
503                  * This thread may hit another WARN() in the panic path.
504                  * Resetting this prevents additional WARN() from
panicking the
505                  * system on this thread.  Other threads are blocked by the
506                  * panic_mutex in panic().
507                  */

I interpreted it as recursion into panic will cause a deadlock due to
recursive mutex acquisition.

But the mutex is a custom CAS that supports recursion on the same CPU.

136         this_cpu = raw_smp_processor_id();
137         old_cpu  = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
138
139         if (old_cpu != PANIC_CPU_INVALID && old_cpu != this_cpu)
140                 panic_smp_self_stop();


Mailed v2.

Thanks!


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

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