linux-kernel - Re: [PATCHv3 4/5] mm: make compound

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: <alpine.LSU.2.11.1508271004200.2999@eggly.anvils>
Date:	Thu, 27 Aug 2015 10:28:48 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Michal Hocko <mhocko@...nel.org>
cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Hugh Dickins <hughd@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Johannes Weiner <hannes@...xchg.org>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCHv3 4/5] mm: make compound_head() robust

On Thu, 27 Aug 2015, Michal Hocko wrote:
> On Thu 27-08-15 17:09:17, Michal Hocko wrote:
> [...]
> > Btw. Do we need the same think for page::mapping and KSM?
> 
> I guess we are safe here because the address for mappings comes from
> kmalloc and that aligned properly, right?

Not quite right, in fact.  Because usually the struct address_space
is embedded within the struct inode (at i_data), and the struct inode
embedded within the fs-dependent inode, and that's what's kmalloc'ed.

What makes the mapping pointer low bits safe is include/linux/fs.h:
struct address_space {
	...
} __attribute__((aligned(sizeof(long))));

Which we first had to add in for the cris architecture, which stumbled
not on a genuine allocated address_space, but on that funny statically
declared swapper_space in mm/swap_state.c.

But struct anon_vma and KSM's struct stable_node (which depend on
the same scheme for low bits of page->mapping) have no such alignment
attribute specified: those ones are indeed relying on the kmalloc
guarantee as you suppose.

Does struct rcu_head have no __attribute__((aligned(whatever)))?
Perhaps that attribute should be added when it's needed.

Hugh
--
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/