Date:   Tue, 26 Mar 2019 17:18:47 -0300
From:   Joao Moreira <jmoreira@...e.de>
To:     Joe Lawrence <joe.lawrence@...hat.com>
Cc:     live-patching@...r.kernel.org, mbenes@...e.cz, pmladek@...e.cz,
        jikos@...e.cz, nstange@...e.de, jpoimboe@...hat.com,
        khlebnikov@...dex-team.ru, jeyu@...nel.org, matz@...e.de,
        linux-kernel@...r.kernel.org, yamada.masahiro@...ionext.com,
        linux-kbuild@...r.kernel.org, michal.lkml@...kovi.net
Subject: Re: [PATCH v2 0/8] klp-convert



On 3/18/19 4:18 PM, Joe Lawrence wrote:
> On Fri, Mar 01, 2019 at 11:13:05AM -0300, Joao Moreira wrote:
>> Livepatches may use symbols which are not contained in its own scope,
>> and, because of that, may end up compiled with relocations that will
>> only be resolved during module load. Yet, when the referenced symbols are
>> not exported, solving this relocation requires information on the object
>> that holds the symbol (either vmlinux or modules) and its position inside
>> the object, as an object may contain multiple symbols with the same name.
>> Providing such information must be done accordingly to what is specified
>> in Documentation/livepatch/module-elf-format.txt.
>>
>> Currently, there is no trivial way to embed the required information as
>> requested in the final livepatch elf object. klp-convert solves this
>> problem in two different forms: (i) by relying on a symbol map, which is
>> built during kernel compilation, to automatically infers the relocation
>> targeted symbol, and, when such inference is not possible (ii) by using
>> annotations in the elf object to convert the relocation accordingly to
>> the specification, enabling it to be handled by the livepatch loader.
>>
>> Given the above, add support for symbol mapping in the form of
>> Symbols.list file; add klp-convert tool; integrate klp-convert tool into
>> kbuild; make livepatch modules discernible during kernel compilation
>> pipeline; add data-structure and macros to enable users to annotate
>> livepatch source code; make modpost stage compatible with livepatches;
>> update livepatch-sample and update documentation.
>>
>> The patch was tested under three use-cases:
>>
>> use-case 1: There is a relocation in the lp that can be automatically
>> resolved by klp-convert (tested by removing the annotations from
>> samples/livepatch/livepatch-annotated-sample.c)
>>
>> use-case 2: There is a relocation in the lp that cannot be automatically
>> resolved, as the name of the respective symbol appears in multiple
>> objects. The livepatch contains an annotation to enable a correct
>> relocation - reproducible with this livepatch sample:
>> www.livewire.com.br/suse/klp/livepatch-sample.1.c
>>
>> use-case 3: There is a relocation in the lp that cannot be automatically
>> resolved similarly as 2, but no annotation was provided in the livepatch,
>> triggering an error during compilation - reproducible with this livepatch
>> sample: www.livewire.com.br/suse/klp/livepatch-sample.2.c
>>
>> In comparison with v1, this version of the patch-set:
>> - was rebased to kernel 4.19
>> - adds a Symbols.list versioning information
>> - brings bug fixes and code improvements to klp-convert sources
>>
>> This is a patch-set repost, given that a typo in a mail address prevented
>> the original submission from being posted to lkml.
>>
>> [ ... snip ... ]
> 
> Hi Joao,
> 
> Apologies for taking so long to get to this patchset, but I finally
> spent last week reviewing and testing.  My goal was to write a klp
> self-test based on the implementation and your sample module.  Along the
> way I spotted a few minor bugs and other small suggestions.  Instead of
> dumping a bunch of code or patch content in my replies, I posted my
> rebase and modified branch here:
> 
>    https://github.com/joe-lawrence/linux/tree/klp-convert-v2-rebase-review
> 
> I added subject line [squash] tags to individual commits that should be
> considered fixups for patches in this set.  Those commit logs also
> contain [joe: description] tags and my sign-offs for that purpose as
> well.
> 
> Hopefully this form of feedback will be easy to digest.  I'll reply to
> the individual patchs here with high-level comments and a pointer to the
> corresponding github patch.  Let me know if there are any questions.  If
> it is easier to simply repost as a v3 with those changes, I can do that
> as well -- whichever method is easier for you.
> 

Hi Joe, again thanks a lot for the review. To the things which I had 
something to say, I already replied to the respective messages. If none 
has issues with the fix for the ppc64le .TOC. symbols issue (on patch 
5/8) and with the fix for the multi-used-m Makefile (on patch 2/8), I 
guess we are good for moving forward to a v3.

If you don't mind, this is fine by me that you squash the changes and 
post the newer version. In fact, I can't figure out why my patch 
submissions did not appear in lkml (if someone knows what could be the 
reason, please, let me know), so I guess it would be nice to have it 
reachable this time.

Tks,
Joao

> I'll also take comments on my work-in-progress self-test for
> klp-convert:
> 
>    [new] livepatch/selftests: add klp-convert
>    https://github.com/torvalds/linux/commit/b0d858b9356d3c909096509a0f18e092b739b44f
> 
> At the moment, it consists of two livepatch modules (I'd prefer to
> consolidate, but ran into an issue with klp-convert and multiple object
> files) and verifies that livepatch can correctly resolve sympos of 0/1,
> 2 for unique/non-uniquely named strings and functions.
> 
> -- Joe
> 

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