Re: [Xen-devel] Problems with livepatching

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 11/24/2016 01:08 AM, Konrad Rzeszutek Wilk wrote:
> On Thu, Nov 24, 2016 at 12:13:43AM +0000, M A Young wrote:
> > On Wed, 23 Nov 2016, Andrew Cooper wrote:
> >
> > > 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.
> > Where is this latest version available from? I had checked the git repo on
> > xenbits
> > http://xenbits.xenproject.org/gitweb/?p=livepatch-build-tools.git;a=summary
> > but the last commit was 4 months ago.
> Here is the patch that Ross has been working on - it is being first reviewed
> for merge in the upstream version of kpatch. Hence hasn't been posted. But
> posting it here.
I've also got a patch to fix the build with GCC 6 which I shall send out 
shortly. This should fix the 'Unknown symbol' issue.
--
Ross Lagerwall

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