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Re: Fix issue with alternatives/paravirt patches

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+++ 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

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[PATCH 0/2] Fix issue with alternatives/paravirt patches Jessica Yu <jeyu@redhat.com> - 2016-07-06 04:40 +0200
  [PATCH 2/2] livepatch/x86: apply alternatives and paravirt patches after relocations Jessica Yu <jeyu@redhat.com> - 2016-07-06 04:40 +0200
    Re: [PATCH 2/2] livepatch/x86: apply alternatives and paravirt  patches after relocations Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-08 17:50 +0200
  [PATCH 1/2] livepatch: use arch_klp_init_object_loaded() to finish arch-specific tasks Jessica Yu <jeyu@redhat.com> - 2016-07-06 04:40 +0200
  Re: [PATCH 0/2] Fix issue with alternatives/paravirt patches Petr Mladek <pmladek@suse.com> - 2016-07-07 18:00 +0200
    Re: [PATCH 0/2] Fix issue with alternatives/paravirt patches Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-08 01:00 +0200
      Re: [PATCH 0/2] Fix issue with alternatives/paravirt patches Miroslav Benes <mbenes@suse.cz> - 2016-07-12 14:00 +0200
        Re: [PATCH 0/2] Fix issue with alternatives/paravirt patches Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-12 16:10 +0200
          Re: Fix issue with alternatives/paravirt patches Jessica Yu <jeyu@redhat.com> - 2016-07-13 03:20 +0200
    Re: Fix issue with alternatives/paravirt patches Jessica Yu <jeyu@redhat.com> - 2016-07-08 02:00 +0200
  Re: [PATCH 0/2] Fix issue with alternatives/paravirt patches Christopher Arges <chris.j.arges@canonical.com> - 2016-07-08 07:30 +0200
    Re: Fix issue with alternatives/paravirt patches Jessica Yu <jeyu@redhat.com> - 2016-07-08 19:00 +0200
  Re: [PATCH 0/2] Fix issue with alternatives/paravirt patches Miroslav Benes <mbenes@suse.cz> - 2016-07-12 14:10 +0200
    Re: Fix issue with alternatives/paravirt patches Jessica Yu <jeyu@redhat.com> - 2016-07-21 07:20 +0200
      Re: Fix issue with alternatives/paravirt patches Miroslav Benes <mbenes@suse.cz> - 2016-07-21 10:50 +0200

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