linux-kernel - Re: [PATCH v1] hugetlbfs: don't access uninitialized memmaps in pfn_range_valid

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Date:   Tue, 15 Oct 2019 11:34:11 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, Michal Hocko <mhocko@...nel.org>,
        stable@...r.kernel.org,
        Anshuman Khandual <anshuman.khandual@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1] hugetlbfs: don't access uninitialized memmaps in
 pfn_range_valid_gigantic()

On 10/15/19 5:07 AM, David Hildenbrand wrote:
> Uninitialized memmaps contain garbage and in the worst case trigger
> kernel BUGs, especially with CONFIG_PAGE_POISONING. They should not get
> touched.
> 
> Let's make sure that we only consider online memory (managed by the
> buddy) that has initialized memmaps. ZONE_DEVICE is not applicable.
> 
> page_zone() will call page_to_nid(), which will trigger
> VM_BUG_ON_PGFLAGS(PagePoisoned(page), page) with CONFIG_PAGE_POISONING
> and CONFIG_DEBUG_VM_PGFLAGS when called on uninitialized memmaps. This
> can be the case when an offline memory block (e.g., never onlined) is
> spanned by a zone.
> 
> Note: As explained by Michal in [1], alloc_contig_range() will verify
> the range. So it boils down to the wrong access in this function.
> 
> [1] http://lkml.kernel.org/r/20180423000943.GO17484@dhcp22.suse.cz
> 
> Reported-by: Michal Hocko <mhocko@...nel.org>
> Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319
> Cc: stable@...r.kernel.org # v4.13+
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Signed-off-by: David Hildenbrand <david@...hat.com>

Thanks David,

Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>

-- 
Mike Kravetz