Re: [PATCH] libxc: remove most of tools/libxc/xc_dom_compat_linux.c

[Juergen Gross <jgross@suse.com>]

On 10/06/2015 03:17 PM, Ian Campbell wrote:
> On Tue, 2015-10-06 at 14:06 +0100, Andrew Cooper wrote:
>> 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.
>
> No it isn't.
>
> xc_dom_linux_build is implemented in terms of the non-compat xc_dom_*
> functions, so it should be possible to do what you want with out using the
> compat wrapper.
>
> If there is some obscure reason this isn't the case then we should fix
> that, not carry around the compat options for ever as a workaround (fixes
> include but are not limited to promoting xc_dom_linux_build into a non
> -compat helper).

Any further comments?

Andrew, are you okay with Ian's statement?

Ian, does this mean you are Ack-ing the patch?


Juergen