linux-kernel - Re: [PATCH 3/3] flush_tlb_range() needs ->page_table_lock when ->mmap

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: <20120305205354.GM23916@ZenIV.linux.org.uk>
Date:	Mon, 5 Mar 2012 20:53:54 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] flush_tlb_range() needs ->page_table_lock when
 ->mmap_sem is not held

On Mon, Mar 05, 2012 at 12:30:19PM -0800, Linus Torvalds wrote:
> Is this safe? And why does it need it? Please add more explanations.

a) safety - as the matter of fact, all other callers either hold either
->mmap_sem (exclusive) or ->page_table_lock.  flush_tlb_range() is
called under ->page_table_lock in a lot of places, e.g.
page_referenced_one() -> pmdp_clear_flush_young_notify() ->
-> pmdp_clear_flush_young() -> flush_tlb_range(), with
                /* go ahead even if the pmd is pmd_trans_splitting() */
                if (pmdp_clear_flush_young_notify(vma, address, pmd))
                        referenced++;
                spin_unlock(&mm->page_table_lock);
in page_referenced_one().

b) there are instances that work with page tables.  See e.g.
arch/powerpc/mm/tlb_hash32.c, flush_tlb_range() and flush_range() in there.
The same goes for uml, with a lot more extensive playing with page tables.

Almost all callers are actually fine - flush_tlb_range() may have no need
to bother playing with page tables, but it can do so safely; again, this
caller is the sole exception - everything else either has exclusive ->mmap_sem
on the mm in question, or mm->page_table_lock is held.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/