Re:Re: [PATCH] arm/kasan:fix the arry size of kasan_early_shadow_pte

[hailong <hailongliiu@xxxxxxxx>]

At 2021-01-10 05:26:08, "Linus Walleij" <linus.walleij@xxxxxxxxxx> wrote:
>On Sat, Jan 9, 2021 at 5:51 AM Hailong liu <hailongliiu@xxxxxxxx> wrote:
>
>> From: Hailong Liu <liu.hailong6@xxxxxxxxxx>
>>
>> The size of kasan_early_shadow_pte[] now is PTRS_PER_PTE which defined to
>> 512 for arm architecture. This means that it only covers the prev Linux pte
>> entries, but not the HWTABLE pte entries for arm.
>>
>> The reason it works well current is that the symbol kasan_early_shadow_page
>> immediately following kasan_early_shadow_pte in memory is page aligned,
>> which makes kasan_early_shadow_pte look like a 4KB size array. But we can't
>> ensure the order always right with different compiler/linker, nor more bss
>> symbols be introduced.
>>
>> We had a test with QEMU + vexpress：put a 512KB-size symbol with attribute
>> __section(".bss..page_aligned") after kasan_early_shadow_pte, and poison it
>> after kasan_early_init(). Then enabled CONFIG_KASAN, it failed to boot up.
>>
>> Signed-off-by: Hailong Liu <liu.hailong6@xxxxxxxxxx>
>> Signed-off-by: Ziliang Guo <guo.ziliang@xxxxxxxxxx>
>
>OK I see the problem, I think.
>
>> +#ifndef PTE_HWTABLE_PTRS
>> +#define PTE_HWTABLE_PTRS 0
>> +#endif
>
>Can this even happen? We have either pgtable-2level.h or
>pgtable-3level.h, both of which define PTE_HWTABLE_PTRS.
>

I guess not for arm. But I'm not sure for other ARCHs.

>>  extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
>> -extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE];
>> +extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE + PTE_HWTABLE_PTRS];
>
>Yeah this looks exactly like bm_pte so it makes sense.
>

Yes, it comes from prototype of pm_pte. And it does solve the
problems our project encountered and seems to work well for now.

>If you drop the first ifndef,
>Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
>
>Yours,
>Linus Walleij

Thanks.