Re: [PATCH v2 4/4] powerpc: Book3S 64-bit "heavyweight" KASAN support

Daniel Axtens
2019-12-12T13:41:14Z

Hi Christophe,

I think I've covered everything you've mentioned in the v3 I'm about to
send, except for:

>> + /* mark early shadow region as RO and wipe */
>> + pte = __pte(__pa(kasan_early_shadow_page) |
>> + pgprot_val(PAGE_KERNEL_RO) | _PAGE_PTE);
>
> Any reason for _PAGE_PTE being required here and not being included in
> PAGE_KERNEL_RO ?

I'm not 100% sure quite what you mean here. I think you're asking: why
do we need to supply _PAGE_PTE here, shouldn't PAGE_KERNEL_RO set that
bit or cover that case?

_PAGE_PTE is defined by section 5.7.10.2 of Book III of ISA 3.0: bit 1
(linux bit 62) is 'Leaf (entry is a PTE)' I originally had this because
it was set in Balbir's original implementation, but the bit is also set
by pte_mkpte which is called in set_pte_at, so I also think it's right
to set it.

I don't know why it's not included in the permission classes; I suspect
it's because it's not conceptually a permission, it's set and cleared in
things like swp entry code.

Does that answer your question?

Regards,
Daniel