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xen-devel
Re: [Xen-devel] [PATCH][P2M] add printk to NP PAE logic in p2m
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To: |
Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> |
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Subject: |
Re: [Xen-devel] [PATCH][P2M] add printk to NP PAE logic in p2m |
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From: |
"Stephen C. Tweedie" <sct@xxxxxxxxxx> |
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Date: |
Wed, 16 Jan 2008 16:52:45 +0000 |
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Cc: |
Stephen Tweedie <sct@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Woller, Thomas" <thomas.woller@xxxxxxx> |
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Wed, 16 Jan 2008 08:58:18 -0800 |
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Hi,
On Tue, 2008-01-15 at 19:31 +0000, Keir Fraser wrote:
> If we add that printk() then it's on a path triggerable by an HVM guest (via
> the populate_physmap hypercall, for example) and there is a potential DoS
> attack. The need to modify the Xen command line to enable NPT on PAE
> hypervisor should really be caveat enough anyway.
Hardly, there's no reason at all for a user to assume that enabling NPT
in that situation will cause guest address spaces to be truncated.
Ideally we'd have a text message delivered back to the user on all
domain creations when this truncation happens. A log message is
probably the minimum reasonable notification; truncating silently is a
pretty poor option.
There are plenty of solutions --- simply do the printk once per domain,
for example, or rate-limit it, or don't do it when the physmap is
populated but have a separate test at domain build time. But truncating
silently seems to be one of the worst alternatives.
Cheers,
Stephen
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