linux-kernel - Re: still nfs problems [Was: Linux 2.6.37-rc8]

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]

Date:	Wed, 5 Jan 2011 11:18:14 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Marc Kleine-Budde <m.kleine-budde@...gutronix.de>,
	linux-arm-kernel@...ts.infradead.org,
	Parisc List <linux-parisc@...r.kernel.org>,
	linux-arch@...r.kernel.org
Subject: Re: still nfs problems [Was: Linux 2.6.37-rc8]

On Wed, Jan 5, 2011 at 11:05 AM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
>
> I think the solution for the kernel direct mapping problem is to take
> the expected flushes and invalidates into kmap/kunmap[_atomic].

No, we really can't do that. Most of the time, the kmap() is the only
way we access the page anyway, so flushing things would just be
stupid. Why waste time and energy on doing something pointless?

In fact, kmap() here is a total non-issue. It's not the kmap() that
introduces any virtual aliases, and never has been. It's the
"vm_map_ram()" that is the problem. Unlike the kmap(), that really
_does_ introduce a virtual alias, and is a problem for any virtual
cache.

So don't blame kmap(). It's innocent and irrelevant - the bug could
happen entirely without it (think a 64-bit address space that doesn't
even _have_ kmap, but has software that mixes vm_map_ram() with
non-mapped accesses).

                           Linus
--
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/