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

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Date:   Fri, 13 Dec 2019 00:41:14 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     Christophe Leroy <christophe.leroy@....fr>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kasan-dev@...glegroups.com,
        aneesh.kumar@...ux.ibm.com, bsingharora@...il.com
Subject: Re: [PATCH v2 4/4] powerpc: Book3S 64-bit "heavyweight" KASAN support

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