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SubjectRe: [PATCH v2 06/18] x86/kasan/64: Teach KASAN about the cpu_entry_area
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On 11/22/2017 06:22 PM, Andy Lutomirski wrote:
> On Wed, Nov 22, 2017 at 1:05 AM, Andrey Ryabinin
> <aryabinin@virtuozzo.com> wrote:
>>
>>
>> On 11/22/2017 07:44 AM, Andy Lutomirski wrote:
>>> The cpu_entry_area will contain stacks. Make sure that KASAN has
>>> appropriate shadow mappings for them.
>>>
>>> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
>>> Cc: Alexander Potapenko <glider@google.com>
>>> Cc: Dmitry Vyukov <dvyukov@google.com>
>>> Cc: kasan-dev@googlegroups.com
>>> Signed-off-by: Andy Lutomirski <luto@kernel.org>
>>> ---
>>> arch/x86/mm/kasan_init_64.c | 9 ++++++++-
>>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
>>> index 99dfed6dfef8..43d376687315 100644
>>> --- a/arch/x86/mm/kasan_init_64.c
>>> +++ b/arch/x86/mm/kasan_init_64.c
>>> @@ -330,7 +330,14 @@ void __init kasan_init(void)
>>> early_pfn_to_nid(__pa(_stext)));
>>>
>>> kasan_populate_zero_shadow(kasan_mem_to_shadow((void *)MODULES_END),
>>> - (void *)KASAN_SHADOW_END);
>>> + kasan_mem_to_shadow((void *)(__fix_to_virt(FIX_CPU_ENTRY_AREA_BOTTOM))));
>>> +
>>> + kasan_populate_shadow((unsigned long)kasan_mem_to_shadow((void *)(__fix_to_virt(FIX_CPU_ENTRY_AREA_BOTTOM))),
>>> + (unsigned long)kasan_mem_to_shadow((void *)(__fix_to_virt(FIX_CPU_ENTRY_AREA_TOP) + PAGE_SIZE)),
>>
>> What's '+ PAGE_SIZE' for?
>>
>
> __fix_to_virt(..._TOP) returns the address of the *bottom* of the last
> cpu_entry_area page. +PAGE_SIZE returns one past the end of the
> region, which I assume is the correct thing to pass.
>

Right.

Perhaps, it would be better to use variables, just avoid such awfully long lines, I mean like this:
fixmap_shadow_start = (void *)__fix_to_virt(FIX_CPU_ENTRY_AREA_BOTTOM);
fixmap_shadow_start = kasan_mem_to_shadow(fixmap_shadow_start);

fixmap_shadow_end = (void *)__fix_to_virt(FIX_CPU_ENTRY_AREA_TOP) + PAGE_SIZE;
fixmap_shadow_end = kasan_mem_to_shadow(fixmap_shadow_end);

kasan_populate_zero_shadow(kasan_mem_to_shadow((void *)MODULES_END),
fixmap_shadow_start);

kasan_populate_shadow((unsigned long)fixmap_shadow_start,
(unsigned long)fixmap_shadow_end,
0);

I'm also thinking that we should change kasan_populate_shadow() to take void* instead of 'unsigned long'
to avoid those casts.

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