Subject: Re: [PATCH v2] kasan: Support for r/w instrumentation control
To: Dmitry Vyukov <dvyukov@google.com>
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CC: Maninder Singh <maninder1.s@samsung.com>,
        Alexander Potapenko <glider@google.com>,
        Jonathan Corbet <corbet@lwn.net>, Michal Marek <mmarek@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        kasan-dev <kasan-dev@googlegroups.com>, <linux-doc@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "open list:KERNEL BUILD + fi..." <linux-kbuild@vger.kernel.org>,
        PANKAJ MISHRA <pankaj.m@samsung.com>,
        Ajeet Kumar Yadav <ajeet.y@samsung.com>,
        Vaneet narang <v.narang@samsung.com>
From: Andrey Ryabinin <aryabinin@virtuozzo.com>
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Date: Tue, 13 Dec 2016 16:59:37 +0300
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On 12/13/2016 12:38 PM, Dmitry Vyukov wrote:
> On Tue, Dec 13, 2016 at 10:20 AM, Andrey Ryabinin
> <aryabinin@virtuozzo.com> wrote:
>>
>>
>> On 12/13/2016 11:58 AM, Dmitry Vyukov wrote:
>>
>>> --- a/Documentation/dev-tools/kasan.rst
>>> +++ b/Documentation/dev-tools/kasan.rst
>>> @@ -40,6 +40,14 @@ similar to the following to the respective kernel Makefile:
>>>
>>>      KASAN_SANITIZE := n
>>>
>>> +Sometimes it may be useful to disable instrumentation of reads, or writes
>>> +or both for the entire kernel. For example, if binary size is a concern,
>>> +it may be useful to disable instrumentation of reads to reduce binary size but
>>> +still catch more harmful bugs on writes. Or, if one is interested only in
>>> +sanitization of a particular module and performance is a concern, she can
>>> +disable instrumentation of both reads and writes for kernel code.
>>> +Instrumentation can be disabled with CONFIG_KASAN_READS and
>>> CONFIG_KASAN_WRITES.
>>> +
>>
>> I don't understand this. How this can be related to modules? Configs are global.
>> You can't just disable/enable config per module.
> 
> 
> Build everything without instrumentation. Then enable instrumentation
> and do "make lib/test_kasan.ko".
> Or build everything, copy out bzImage, change config, build everything again.

Yeah, this is soooooo convenient...

Seriously speaking, per-file instrumentation is absolutely irrelevant to this patch and should have been
addressed from a different angle. E.g. see how UBSAN/GCOV/KCOV do that.

As for this patch, I'd say only one option would be enough - KASAN_DONT_SANITIZE_READS.
Nobody wants to sanitize only reads without writes, right? Writes are fewer and more dangerous.