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. 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
