linux-kernel - Re: [PATCH v4 3/3] powerpc/32: Add KASAN support

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Message-ID: <c5599614-128b-69a8-2526-72b135070e8d@virtuozzo.com>
Date:   Tue, 12 Feb 2019 15:14:40 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Daniel Axtens <dja@...ens.net>,
        Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        PowerPC <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH v4 3/3] powerpc/32: Add KASAN support

On 2/12/19 2:38 PM, Christophe Leroy wrote:
> 
> 
> Le 12/02/2019 à 02:08, Daniel Axtens a écrit :
>> Andrey Ryabinin <aryabinin@...tuozzo.com> writes:
>>
>>>
>>> Christophe, you can specify KASAN_SHADOW_OFFSET either in Kconfig (e.g. x86_64) or
>>> in Makefile (e.g. arm64). And make early mapping writable, because compiler generated code will write
>>> to shadow memory in function prologue/epilogue.
>>
>> Hmm. Is this limitation just that compilers have not implemented
>> out-of-line support for stack instrumentation, or is there a deeper
>> reason that stack/global instrumentation relies upon inline
>> instrumentation?
> 
> No, it looks like as soon as we define KASAN_SHADOW_OFFSET in Makefile in addition to asm/kasan.h, stack instrumentation works with out-of-line.
> 


I think you confusing two different things.
CONFIG_KASAN_INLINE/CONFIG_KASAN_OUTLINE affects only generation of code that checks memory accesses,
whether we call __asan_loadx()/__asan_storex() or directly insert code, checking shadow memory. 

But with stack instrumentation we also need to poison redzones around stack variables and unpoison them
when we leave the function. That poisoning/unpoisoning thing is always inlined. Currently there is no option to make it out-of-line.

So you can have stack instrumentation with KASAN_OUTLINE, but it just means that checking shadow memory on memory access will be outlined,
poisoning/unpoisoing stack redzones will remain inlined.