Re: [xen-4.1.6.1] SIGSEGV libxc/xc_save_domain.c: p2m_size >> configured_ram_size

[Philipp Hahn <hahn@univention.de>]

Hello Georg,

first of all thank you for answering.

Am 13.06.2016 um 12:15 schrieb George Dunlap:
> On Fri, Jun 10, 2016 at 4:22 PM, Philipp Hahn <hahn@univention.de> wrote:
>> while trying to live migrate some VMs from an xen-4.1.6.1 host "xc_save"
>> crashes with a segmentation fault in tools/libxc/xc_domain_save.c:1141
>>>         /*
>>>          * Quick belt and braces sanity check.
>>>          */
>>>         for ( i = 0; i < dinfo->p2m_size; i++ )
>>>         {
>>>             mfn = pfn_to_mfn(i);
>>>             if( (mfn != INVALID_P2M_ENTRY) && (mfn_to_pfn(mfn) != i) )
>>                                                  ^^^^^^^^^^^^^^^
>> due to a de-reference through
>>> #define pfn_to_mfn(_pfn)                                            \
>>>   ((xen_pfn_t) ((dinfo->guest_width==8)                               \
>>>                 ? (((uint64_t *)ctx->live_p2m)[(_pfn)])                  \
>>>                 : ((((uint32_t *)ctx->live_p2m)[(_pfn)]) == 0xffffffffU  \
>>>                    ? (-1UL) : (((uint32_t *)ctx->live_p2m)[(_pfn)]))))
...
> Given that 4.1 is long out of support, we won't be making a proper fix
> in-tree (since it will never be released).

I know that 4.1 is EOL.
I'm aware of Ubuntu still having xen-4.1 in one of their LTS versions
(Precise) and its also in Debian-oldstable, which a lot people (us
included) still use. I would prefer to update, but I can for reasons
outside my direct control.

I'm already working with Stefan Bader from Canonical to backport most of
the XSAs to 4.1, so there already exists a "better" version outside of
the official Xen repositories.

> So what kind of resolution
> would be the most help to you?  A patch you can apply locally to allow
> the save/restore to work?

A patch is okay. I've already fixed a lot other bugs in xen-4.1 by
patching the last release, so compiling my own version is no problem for me.

Philipp

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