linux-kernel - Re: [PATCH v2] arm64: mm: Fix memmap to be initialized for the entire section

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] [day] [month] [year] [list]

Date:   Mon, 12 Dec 2016 12:02:42 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Robert Richter <robert.richter@...ium.com>
Cc:     Yisheng Xie <xieyisheng1@...wei.com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        David Daney <david.daney@...ium.com>,
        Mark Rutland <mark.rutland@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] arm64: mm: Fix memmap to be initialized for the entire section

On 9 December 2016 at 14:52, Robert Richter <robert.richter@...ium.com> wrote:
> On 09.12.16 21:15:12, Yisheng Xie wrote:
>> For invalid pages, their zone and node information is not initialized, and it
>> do have risk to trigger the BUG_ON, so I have a silly question,
>> why not just change the BUG_ON:
>
> We need to get the page handling correct. Modifying the BUG_ON() just
> hides that something is wrong.
>

Actually, I think this is a reasonable question. We are trying very
hard to work around the BUG_ON(), which arguably does something wrong
by calling page_to_nid() on a struct page without checking if it is a
valid page.

Looking at commit 344c790e3821 ("mm: make setup_zone_migrate_reserve()
aware of overlapping nodes"), the BUG_ON() has a specific purpose
related to adjacent zones.

What will go wrong if we ignore this check?


>
>> -----------
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 6de9440..af199b8 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1860,12 +1860,13 @@ int move_freepages(struct zone *zone,
>>          * Remove at a later date when no bug reports exist related to
>>          * grouping pages by mobility
>>          */
>> -       VM_BUG_ON(page_zone(start_page) != page_zone(end_page));
>> +       VM_BUG_ON(early_pfn_valid(start_page) && early_pfn_valid(end_page) &&
>> +                       page_zone(start_page) != page_zone(end_page));
>>  #endif
>>
>>         for (page = start_page; page <= end_page;) {
>>                 /* Make sure we are not inadvertently changing nodes */
>> -               VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page);
>> +               VM_BUG_ON_PAGE(early_pfn_valid(page) && (page_to_nid(page) != zone_to_nid(zone)), page);
>>
>>                 if (!pfn_valid_within(page_to_pfn(page))) {
>>                         page++;
>