linux-kernel - Re: Interaction between Xen and XFS: stray RW mappings

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: <471CEEB4.9040807@goop.org>
Date:	Mon, 22 Oct 2007 11:40:52 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andi Kleen <andi@...stfloor.org>
CC:	dean gaudet <dean@...tic.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Xen-devel <xen-devel@...ts.xensource.com>, Morten@...e.de,
	David Chinner <dgc@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Bøgeskov <xen-users@...ten.bogeskov.dk>,
	xfs@....sgi.com, xfs-masters@....sgi.com,
	Mark Williamson <mark.williamson@...cam.ac.uk>
Subject: Re: Interaction between Xen and XFS: stray RW mappings

Andi Kleen wrote:
> Jeremy Fitzhardinge <jeremy@...p.org> writes:
>   
>> Yes, that's precisely the problem.  xfs does delay the unmap, leaving
>> stray mappings, which upsets Xen.
>>     
>
> Again it not just upsets Xen, keeping mappings to freed pages is wrong generally 
> and violates the x86 (and likely others like PPC) architecture because it can 
> cause illegal caching attribute aliases.
>
> The patch that went into the tree was really not correct -- this
> bogus optimization should have been unconditionally removed
> or if you really wanted an ifdef made dependent on !CONFIG_XEN &&
> !CONFIG_AGP (and likely && !CONFIG_DRM && !CONFIG_anything else that
> uses uncached mappings in memory). 
>
> You just worked around the obvious failure and leave the non obvious
> rare corruptions in, which isn't a good strategy.

Well, at least it becomes a known issue and/or placeholder for when Nick
does his grand unified vmap manager.  I guess a clean workaround would
be to add a CONFIG_XFS_LAZY_UNMAP, and do it at the Kconfig level... 
I'll cook up a patch.

    J
-
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/