Re: [PATCH v4 5/7] mm, kasan: Stackdepot implementation. Enable stackdepot for SLAB

[Andrey Ryabinin <ryabinin.a.a@gmail.com>]

2016-03-04 17:52 GMT+03:00 Alexander Potapenko <glider@google.com>:
> On Tue, Mar 1, 2016 at 12:57 PM, Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
>>
>>
>> On 02/29/2016 08:12 PM, Dmitry Vyukov wrote:
>>
>>>>> diff --git a/lib/Makefile b/lib/Makefile
>>>>> index a7c26a4..10a4ae3 100644
>>>>> --- a/lib/Makefile
>>>>> +++ b/lib/Makefile
>>>>> @@ -167,6 +167,13 @@ obj-$(CONFIG_SG_SPLIT) += sg_split.o
>>>>>  obj-$(CONFIG_STMP_DEVICE) += stmp_device.o
>>>>>  obj-$(CONFIG_IRQ_POLL) += irq_poll.o
>>>>>
>>>>> +ifeq ($(CONFIG_KASAN),y)
>>>>> +ifeq ($(CONFIG_SLAB),y)
>>>>
>>>> Just try to imagine that another subsystem wants to use stackdepot. How this gonna look like?
>>>>
>>>> We have Kconfig to describe dependencies. So, this should be under CONFIG_STACKDEPOT.
>>>> So any user of this feature can just do 'select STACKDEPOT' in Kconfig.
>>>>
>>>>> +     obj-y   += stackdepot.o
>>>>> +     KASAN_SANITIZE_slub.o := n
>>                         _stackdepot.o
>>
>>
>>>>
>>>>> +
>>>>> +     stack->hash = hash;
>>>>> +     stack->size = size;
>>>>> +     stack->handle.slabindex = depot_index;
>>>>> +     stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
>>>>> +     __memcpy(stack->entries, entries, size * sizeof(unsigned long));
>>>>
>>>> s/__memcpy/memcpy/
>>>
>>> memcpy should be instrumented by asan/tsan, and we would like to avoid
>>> that instrumentation here.
>>
>> KASAN_SANITIZE_* := n already takes care about this.
>> __memcpy() is a special thing solely for kasan internals and some assembly code.
>> And it's not available generally.
> As far as I can see, KASAN_SANITIZE_*:=n does not guarantee it.
> It just removes KASAN flags from GCC command line, it does not
> necessarily replace memcpy() calls with some kind of a
> non-instrumented memcpy().
>

With removed kasan cflags '__SANITIZE_ADDRESS__' is not defined,
hence enable the following defines from arch/x86/include/asm/string_64.h:

#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)

/*
 * For files that not instrumented (e.g. mm/slub.c) we
 * should use not instrumented version of mem* functions.
 */

#undef memcpy
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#endif

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