Messages in this thread | | | Date | Fri, 8 Jul 2016 12:57:40 -0400 | From | Jessica Yu <> | Subject | Re: Fix issue with alternatives/paravirt patches |
| |
+++ Christopher Arges [08/07/16 00:22 -0500]: >On Tue, Jul 05, 2016 at 10:34:58PM -0400, Jessica Yu wrote: >> Hi, >> >> A few months ago, Chris Arges reported a bug involving alternatives/paravirt >> patching that was discussed here [1] and here [2]. To briefly summarize the >> bug, patch modules that contained .altinstructions or .parainstructions >> sections would break because these alternative/paravirt patches would be >> applied first by the module loader (see x86 module_finalize()), then >> livepatch would later clobber these patches when applying per-object >> relocations. This lead to crashes and unpredictable behavior. >> >> One conclusion we reached from our last discussion was that we will >> need to introduce some arch-specific code to address this problem. >> This patchset presents a possible fix for the bug by adding a new >> arch-specific arch_klp_init_object_loaded() function that by default >> does nothing but can be overridden by different arches. >> >> To fix this issue for x86, since we can access a patch module's Elf >> sections through mod->klp_info, we can simply delay the calls to >> apply_paravirt() and apply_alternatives() to arch_klp_init_object_loaded(), >> which is called after relocations have been written for an object. >> In addition, for patch modules, .parainstructions and .altinstructions are >> prefixed by ".klp.arch.${objname}" so that the module loader ignores them >> and livepatch can apply them manually. >> >> Currently for kpatch, we don't support including jump table sections in >> the patch module, and supporting .smp_locks is currently broken, so we >> don't consider those sections (for now). >> >> I did some light testing with some patches to kvm and verified that the >> original issue reported in [2] was fixed. >> >> Based on linux-next. >> > >Jessica, > >I was able to test these patches on top of linux-next. I took your kpatch >branch and hacked it a bit to get it working and was able to >apply a patch to 'kvm_arch_vm_ioctl' while running a VM workload. > >Great job! > >Tested-by: Chris J Arges <chris.j.arges@canonical.com>
Excellent, thanks for testing it out Chris!
Jessica
| |