linux-kernel - Re: [PATCH v9 09/12] mm/kasan: kasan specific map populate function

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAOAebxu1310eCrk88EC=Oaw3n90-9RuHZ1KBhPvLu_DyXBNZFQ@mail.gmail.com>
Date:   Mon, 9 Oct 2017 14:42:32 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     Will Deacon <will.deacon@....com>
Cc:     Mark Rutland <mark.rutland@....com>, catalin.marinas@....com,
        linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        x86@...nel.org, kasan-dev@...glegroups.com, borntraeger@...ibm.com,
        heiko.carstens@...ibm.com, davem@...emloft.net,
        willy@...radead.org, mhocko@...nel.org, ard.biesheuvel@...aro.org,
        sam@...nborg.org, mgorman@...hsingularity.net,
        Steve Sistare <steven.sistare@...cle.com>,
        daniel.m.jordan@...cle.com, bob.picco@...cle.com
Subject: Re: [PATCH v9 09/12] mm/kasan: kasan specific map populate function

Hi Will,

In addition to what Michal wrote:

> As an interim step, why not introduce something like
> vmemmap_alloc_block_flags and make the page-table walking opt-out for
> architectures that don't want it? Then we can just pass __GFP_ZERO from
> our vmemmap_populate where necessary and other architectures can do the
> page-table walking dance if they prefer.

I do not see the benefit, implementing this approach means that we
would need to implement two table walks instead of one: one for x86,
another for ARM, as these two architectures support kasan. Also, this
would become a requirement for any future architecture that want to
add kasan support to add this page table walk implementation.

>> IMO, while I understand that it looks strange that we must walk page
>> table after creating it, it is a better approach: more enclosed as it
>> effects kasan only, and more universal as it is in common code.
>
> I don't buy the more universal aspect, but I appreciate it's subjective.
> Frankly, I'd just sooner not have core code walking early page tables if
> it can be avoided, and it doesn't look hard to avoid it in this case.
> The fact that you're having to add pmd_large and pud_large, which are
> otherwise unused in mm/, is an indication that this isn't quite right imo.

 28 +#define pmd_large(pmd)         pmd_sect(pmd)
 29 +#define pud_large(pud)         pud_sect(pud)

it is just naming difference, ARM64 calls them pmd_sect, common mm and
other arches call them
pmd_large/pud_large. Even the ARM has these defines in

arm/include/asm/pgtable-3level.h
arm/include/asm/pgtable-2level.h

Pavel