Re: [Qemu-devel] virsh dump (qemu guest memory dump?): KASLR enabled linux guest support

[Dave Anderson]

----- Original Message -----
> On 11/09/16 at 11:58am, Wen Congyang wrote:
> > On 11/09/2016 11:17 AM, Dave Young wrote:
> > > Drop qiaonuohan, seems the mail address is wrong..
> > > 
> > > On 11/09/16 at 11:01am, Dave Young wrote:
> > >> Hi,
> > >>
> > >> Latest linux kernel enabled kaslr to randomiz phys/virt memory
> > >> addresses, we had some effort to support kexec/kdump so that crash
> > >> utility can still works in case crashed kernel has kaslr enabled.
> > >>
> > >> But according to Dave Anderson virsh dump does not work, quoted messages
> > >> from Dave below:
> > >>
> > >> """
> > >> with virsh dump, there's no way of even knowing that KASLR
> > >> has randomized the kernel __START_KERNEL_map region, because there is no
> > >> virtual address information -- e.g., like "SYMBOL(_stext)" in the kdump
> > >> vmcoreinfo data to compare against the vmlinux file symbol value.
> > >> Unless virsh dump can export some basic virtual memory data, which
> > >> they say it can't, I don't see how KASLR can ever be supported.
> > >> """
> > >>
> > >> I assume virsh dump is using qemu guest memory dump facility so it
> > >> should be first addressed in qemu. Thus post this query to qemu devel
> > >> list. If this is not correct please let me know.
> > 
> > IIRC, 'virsh dump --memory-only' uses dump-guest-memory, and 'virsh dump'
> > uses migration to dump.
> 
> Do they need different fixes? Dave, I guess you mean --memory-only, but
> could you clarify and confirm it?

As I understand it, the "--memory-only" option uses a new "dump-guest-memory"
QEMU monitor command that creates an ELF kdump vmcore clone. 

Dave


> 
> > 
> > I think I should study kaslr first...
> 
> Thanks for taking care of it.
> 
> > 
> > Thanks
> > Wen Congyang
> > 
> > >>
> > >> Could you qemu dump people make it work? Or we can not support virt dump
> > >> as long as KASLR being enabled. Latest Fedora kernel has enabled it in
> > >> x86_64.
> > >>
> > >> Thanks
> > >> Dave
> > > 
> > > 
> > > 
> > 
> > 
> > 
>