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: <200710221439.21503.nickpiggin@yahoo.com.au>
Date:	Mon, 22 Oct 2007 14:39:21 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	dean gaudet <dean@...tic.org>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>, David Chinner <dgc@....com>,
	xfs@....sgi.com, Xen-devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mark Williamson <mark.williamson@...cam.ac.uk>,
	Morten Bøgeskov <xen-users@...ten.bogeskov.dk>,
	xfs-masters@....sgi.com
Subject: Re: Interaction between Xen and XFS: stray RW mappings

On Monday 22 October 2007 14:28, dean gaudet wrote:
> On Sun, 21 Oct 2007, Jeremy Fitzhardinge wrote:
> > dean gaudet wrote:
> > > On Mon, 15 Oct 2007, Nick Piggin wrote:
> > >> Yes, as Dave said, vmap (more specifically: vunmap) is very expensive
> > >> because it generally has to invalidate TLBs on all CPUs.
> > >
> > > why is that?  ignoring 32-bit archs we have heaps of address space
> > > available... couldn't the kernel just burn address space and delay
> > > global TLB invalidate by some relatively long time (say 1 second)?
> >
> > Yes, that's precisely the problem.  xfs does delay the unmap, leaving
> > stray mappings, which upsets Xen.
>
> sounds like a bug in xen to me :)

You could call it a bug I think. I don't know much about Xen though,
whether or not it expects to be able to run an arbitrary OS kernel.

Presumably, the hypervisor _could_ write protect and trap writes to
*all* page table page mappings.
-
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/