Message-ID: <d2187ca1-2e94-fc5b-a8db-e2123981a5fc@redhat.com>
Date:   Tue, 7 Feb 2023 10:54:53 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Marcos Paulo de Souza <mpdesouza@...e.de>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kbuild@...r.kernel.org
Subject: Re: [RFC PATCH v6 00/12] livepatch: klp-convert tool

On 2/7/23 07:57, Marcos Paulo de Souza wrote:
> On Wed, Feb 16, 2022 at 11:39:28AM -0500, Joe Lawrence wrote:
>> This mostly a rebase update of the livepatch klp-convert tool used to
>> generate klp-relocation types (explained in the summary below).
>>
>> I'm marking this as an RFC as it hasn't been extensively tested for all
>> livepatch supported arches.  There are may be a few symbol annotation
>> changes pending what may be implemented for the FGKASLR patchset, I've
>> left a few TODO and // question? marks in the code, etc.  At the same
>> time, I think "CET/IBT support and live-patches" highlighted a potential
>> need for this tooling, so I'm posting it in its current format for
>> discussion.  I'll reply to individual patches to highlight a few points
>> of interest.
>>
>>
>> Summary
>> -------
>>
>> 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 infer 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 a
>> symbols.klp 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.  For example. see the saved_command_line
>> variable in lib/livepatch/test_klp_convert2.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.  See the KLP_MODULE_RELOC / KLP_SYMPOS annotation sections
>> in lib/livepatch/test_klp_convert{1,2}.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 by
>> removing the KLP_MODULE_RELOC / KLP_SYMPOS annotation sections in
>> lib/livepatch/test_klp_convert{1,2}.c.
>>
>> Selftests have been added to exercise these klp-convert use-cases
>> through several tests.
>>
>>
>> Branches
>> --------
>>
>>
>> Previous versions
>> -----------------
>>
>> RFC:
>>   https://lore.kernel.org/lkml/cover.1477578530.git.jpoimboe@redhat.com/
>> v2:
>>   https://lore.kernel.org/lkml/f52d29f7-7d1b-ad3d-050b-a9fa8878faf2@redhat.com/
>> v3:
>>   https://lore.kernel.org/lkml/20190410155058.9437-1-joe.lawrence@redhat.com/
>> v4:
>>   https://lore.kernel.org/lkml/20190509143859.9050-1-joe.lawrence@redhat.com/
>> v5:
>>   (not posted)
>>   https://github.com/joe-lawrence/klp-convert-tree/tree/klp-convert-v5-devel
>> v6:
>>   https://github.com/joe-lawrence/klp-convert-tree/tree/klp-convert-v6
>>   https://github.com/joe-lawrence/klp-convert-tree/tree/klp-convert-v6-devel
> 
> Hi Joe,
> 
> I send reviews to some patches of the v6 batch, but there is currently a v7 in
> your github profile. I believe that I sent Rb for patches that are the same
> between versions.
> 
> The current version is almost one year older already. Do you plan to send v7
> soon?
> 

Hi Marcos,

Thanks for the reviews and indeed, it has been a while since v6.

For v7, I would like to rebase on top of v6.2 so it includes the recent
x86/ppc64le relocation fixes from Song/Josh.

There are still a fair number of design questions that I have.. but a
fresh version will be much easier to test and review.  I'll try to get
it posted in the new few weeks.

-- 
Joe

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