From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH] libxc: remove most of
	tools/libxc/xc_dom_compat_linux.c
Date: Tue, 6 Oct 2015 14:06:59 +0100
Message-ID: <5613C773.5030901@citrix.com>
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	<5613C400.4040209@citrix.com>
	<20151006125858.GB29124@zion.uk.xensource.com>
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To: Wei Liu <wei.liu2@citrix.com>
Cc: Juergen Gross <jgross@suse.com>, stefano.stabellini@eu.citrix.com, ian.jackson@eu.citrix.com, Ian.Campbell@citrix.com, xen-devel@lists.xen.org
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On 06/10/15 13:58, Wei Liu wrote:
> On Tue, Oct 06, 2015 at 01:52:16PM +0100, Andrew Cooper wrote:
>> On 06/10/15 12:35, Juergen Gross wrote:
>>> In tools/libxc/xc_dom_compat_linux.c only xc_linux_build() is currently
>>> being used by an in-tree component (qemu-xen). All other functions are
>>> superfluous wrappers of the domain builder which can be removed.
>>>
>>> Suggested-by: Ian Campbell <ian.campbell@citrix.com>
>>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> Sorry, but NACK.  They are *not* superfluous.
>>
>> XenServer uses them; xc_dom_linux_build() is the only way to apply
>> XSA-25 size restrictions to PV kernels and initrds.
>>
> Could you explain a bit more about this? How could this particular
> function apply restrictions?
>
> Unfortunately XSA-25 is not on XSA page so I have no idea what that is.
>
> Wei.

Older XSAs are listed on the wiki
http://wiki.xen.org/wiki/Security_Announcements

XSA-25 introduced xc_dom_{kernel,ramdisk}_max_size() to set upper
decompression limits on the kernel and initrd.

To use them, a struct xc_dom_image *dom is needed, which means the only
safe way of constructing PV domains is

xc_dom_allocate()
xc_dom_kernel_max_size()
xc_dom_ramdisk_max_size()
xc_dom_linux_build()

To have the decompression limits in place before decompression starts.

~Andrew