Re: [Xen-devel] Problems with livepatching

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 23/11/2016 23:06, M A Young wrote:
> I have been experimenting with live patching with the recent batch of 
> security updates on Fedora xen with very limited success. I had most 
> attempts with a test build of xen-4.8.0-rc6, and of the updates I have 
> tried only xsa192.patch uploads successfully. For example with 
> xsa191.patch the upload fails with the output
> Uploading /tmp/xen-debuginfo/out1/xsa191.livepatch (1561400 bytes)
> Upload failed: /tmp/xen-debuginfo/out1/xsa191.livepatch, error: 2(No such 
> file or directory)!
> and in xl dmesg a long debugging output ends with the line
> (XEN) livepatch_elf.c:295: livepatch: xsa191: Unknown symbol: .LC0
> with a similar line (mostly with .LC0 but with .LC3 in one case) for the 
> other failed attempts. Am I doing something wrong or is there a problem 
> with live patching in this case?

This looks like a problem generating the livepatch itself, not the
livepatching mechanism.

Make sure you are completely up to date with the livepatch tools
userspace.  There was one bug in livepatch generation which was
discovered due to XSA-191 and fixed (actually a preexisting bug even in
Linux), but its symptoms were innocuous until you patched, at which vcpu
context switch blew up.

With that one bug fixed, I can confirm that all of the recent XSAs are
properly livepatchable with the available tools, and confirmed to work.

~Andrew

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