Subject: Re: [PATCH V2 05/10] kasan: Enable arch to hook into kasan callbacks.

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Sun, 30 Aug 2015 18:11:07 +0530

Andrey Ryabinin <[email-masked]> writes:

> 2015-08-26 11:26 GMT+03:00 Aneesh Kumar K.V <[email-masked]>:
>> We add enable/disable callbacks in this patch which architecture
>> can implemement. We will use this in the later patches for architecture
>> like ppc64, that cannot have early zero page kasan shadow region for the
>> entire virtual address space. Such architectures also cannot use
>> inline kasan support.
>>
>> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
>> ---
>>  mm/kasan/kasan.c |  9 +++++++++
>>  mm/kasan/kasan.h | 15 +++++++++++++++
>>  2 files changed, 24 insertions(+)
>>
>> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
>> index 7b28e9cdf1c7..e4d33afd0eaf 100644
>> --- a/mm/kasan/kasan.c
>> +++ b/mm/kasan/kasan.c
>> @@ -43,6 +43,9 @@ static void kasan_poison_shadow(const void *address, size_t size, u8 value)
>>  {
>>         void *shadow_start, *shadow_end;
>>
>> +       if (!kasan_enabled())
>> +               return;
>> +
>
> By the time this function called we already should have shadow,
> so it should be safe to remove this check.
>

I remember hitting that call before enabling kasan completely. Will
check that again. 

>
>>         shadow_start = kasan_mem_to_shadow(address);
>>         shadow_end = kasan_mem_to_shadow(address + size);
>>
>> @@ -51,6 +54,9 @@ static void kasan_poison_shadow(const void *address, size_t size, u8 value)
>>
>>  void kasan_unpoison_shadow(const void *address, size_t size)
>>  {
>> +       if (!kasan_enabled())
>> +               return;
>> +
>
> Ditto.
>
>>         kasan_poison_shadow(address, size, 0);
>>
>>         if (size & KASAN_SHADOW_MASK) {
>> @@ -238,6 +244,9 @@ static __always_inline void check_memory_region(unsigned long addr,
>>  {
>>         struct kasan_access_info info;
>>
>> +       if (!kasan_enabled())
>> +               return;
>> +
>>         if (unlikely(size == 0))
>>                 return;
>>
>> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
>> index a6b46cc94907..deb547d5a916 100644
>> --- a/mm/kasan/kasan.h
>> +++ b/mm/kasan/kasan.h
>> @@ -68,6 +68,21 @@ static inline bool kasan_report_enabled(void)
>>         return !current->kasan_depth;
>>  }
>>
>> +#ifndef kasan_enabled
>> +/*
>> + * Some archs may want to disable kasan callbacks.
>> + */
>> +static inline bool kasan_enabled(void)
>> +{
>> +       return true;
>> +}
>> +#define kasan_enabled kasan_enabled
>
> Why we need this define?

That is to make sure that we don't endup with different definition of
kasan_enabled due to header include errors. Once we select a
particular definition of the overloaded function, it is always good to mark
the function as defined, so that checks like #ifndef kasan_enabled will
always fail. 

>
>> +#else
>> +#ifdef CONFIG_KASAN_INLINE
>> +#error "Kasan inline support cannot work with KASAN arch hooks"
>> +#endif
>> +#endif
>> +
>>  void kasan_report(unsigned long addr, size_t size,
>>                 bool is_write, unsigned long ip);
>>
>> --
>> 2.5.0
>>

-aneesh