From: Vlastimil Babka <vbabka@suse.cz>
To: Pasha Tatashin <pasha.tatashin@soleen.com>,
Matthew Wilcox <willy@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
linux-m68k@lists.linux-m68k.org,
Anshuman Khandual <anshuman.khandual@arm.com>,
Andrew Morton <akpm@linux-foundation.org>,
william.kucharski@oracle.com,
Mike Kravetz <mike.kravetz@oracle.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
schmitzmic@gmail.com, Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Roman Gushchin <guro@fb.com>,
Muchun Song <songmuchun@bytedance.com>,
Wei Xu <weixugc@google.com>, Greg Thelen <gthelen@google.com>,
David Rientjes <rientjes@google.com>,
Paul Turner <pjt@google.com>, Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH v3 1/9] mm: add overflow and underflow checks for page->_refcount
Date: Thu, 27 Jan 2022 19:27:23 +0100 [thread overview]
Message-ID: <b7f580cb-84f7-5c78-5f68-7ab8f67b0811@suse.cz> (raw)
In-Reply-To: <CA+CK2bDHkOQbTrK=GbsGbojAj_6gaAX_8w3cBCd_LWqXt--yZA@mail.gmail.com>
On 1/26/22 20:22, Pasha Tatashin wrote:
> On Wed, Jan 26, 2022 at 1:59 PM Matthew Wilcox <willy@infradead.org> wrote:
>>
>> On Wed, Jan 26, 2022 at 06:34:21PM +0000, Pasha Tatashin wrote:
>> > The problems with page->_refcount are hard to debug, because usually
>> > when they are detected, the damage has occurred a long time ago. Yet,
>> > the problems with invalid page refcount may be catastrophic and lead to
>> > memory corruptions.
>> >
>> > Reduce the scope of when the _refcount problems manifest themselves by
>> > adding checks for underflows and overflows into functions that modify
>> > _refcount.
>>
>> If you're chasing a bug like this, presumably you turn on page
>> tracepoints. So could we reduce the cost of this by putting the
>> VM_BUG_ON_PAGE parts into __page_ref_mod() et al? Yes, we'd need to
>> change the arguments to those functions to pass in old & new, but that
>> should be a cheap change compared to embedding the VM_BUG_ON_PAGE.
>
> This is not only about chasing a bug. This also about preventing
> memory corruption and information leaking that are caused by ref_count
> bugs from happening.
So you mean it like a security hardening feature, not just debugging? To me
it's dubious to put security hardening under CONFIG_DEBUG_VM. I think it's
just Fedora that uses DEBUG_VM in general production kernels?
> Several months ago a memory corruption bug was discovered by accident:
> an engineer was studying a process core from a production system and
> noticed that some memory does not look like it belongs to the original
> process. We tried to manually reproduce that bug but failed. However,
> later analysis by our team, explained that the problem occured due to
> ref_count bug in Linux, and the bug itself was root caused and fixed
> (mentioned in the cover letter). This work would have prevented
> similar ref_count bugs from yielding to the memory corruption
> situation.
>
> Pasha
>
next prev parent reply other threads:[~2022-01-27 18:27 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-26 18:34 [PATCH v3 0/9] Hardening page _refcount Pasha Tatashin
2022-01-26 18:34 ` [PATCH v3 1/9] mm: add overflow and underflow checks for page->_refcount Pasha Tatashin
2022-01-26 18:59 ` Matthew Wilcox
2022-01-26 19:22 ` Pasha Tatashin
2022-01-26 19:45 ` Matthew Wilcox
2022-01-26 22:40 ` Pasha Tatashin
2022-01-27 18:27 ` Vlastimil Babka [this message]
2022-01-27 19:38 ` Pasha Tatashin
2022-01-27 18:30 ` Vlastimil Babka
2022-01-27 19:42 ` Pasha Tatashin
2022-01-26 18:34 ` [PATCH v3 2/9] mm: Avoid using set_page_count() in set_page_recounted() Pasha Tatashin
2022-01-26 18:34 ` [PATCH v3 3/9] mm: remove set_page_count() from page_frag_alloc_align Pasha Tatashin
2022-01-26 18:34 ` [PATCH v3 4/9] mm: avoid using set_page_count() when pages are freed into allocator Pasha Tatashin
2022-01-26 18:34 ` [PATCH v3 5/9] mm: rename init_page_count() -> page_ref_init() Pasha Tatashin
2022-01-26 18:34 ` [PATCH v3 6/9] mm: remove set_page_count() Pasha Tatashin
2022-01-26 18:34 ` [PATCH v3 7/9] mm: simplify page_ref_* functions Pasha Tatashin
2022-01-26 18:34 ` [PATCH v3 8/9] mm: do not use atomic_set_release in page_ref_unfreeze() Pasha Tatashin
2022-01-26 18:34 ` [PATCH v3 9/9] mm: use atomic_cmpxchg_acquire in page_ref_freeze() Pasha Tatashin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=b7f580cb-84f7-5c78-5f68-7ab8f67b0811@suse.cz \
--to=vbabka@suse.cz \
--cc=akpm@linux-foundation.org \
--cc=anshuman.khandual@arm.com \
--cc=geert@linux-m68k.org \
--cc=gthelen@google.com \
--cc=guro@fb.com \
--cc=hannes@cmpxchg.org \
--cc=hughd@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-m68k@lists.linux-m68k.org \
--cc=linux-mm@kvack.org \
--cc=mike.kravetz@oracle.com \
--cc=mingo@redhat.com \
--cc=pasha.tatashin@soleen.com \
--cc=pjt@google.com \
--cc=rientjes@google.com \
--cc=rostedt@goodmis.org \
--cc=schmitzmic@gmail.com \
--cc=songmuchun@bytedance.com \
--cc=weixugc@google.com \
--cc=william.kucharski@oracle.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox