On Fri, 3 May 2019, Joe Lawrence wrote: > On Tue, Apr 16, 2019 at 01:37:13PM +0200, Miroslav Benes wrote: > > > > [ ... snip ... ] > > > > Quick look, but it seems quite similar to the problem we had with > > apply_alternatives(). See arch/x86/kernel/livepatch.c and the commit which > > introduced it. > > That was an interesting diversion :) I think I grok the idea as: > > The kernel supports a few different code-patching methods: > > - SMP locks > - alternatives > - paravirt > - jump labels > > and we need to ensure that they do not prematurely operate on unresolved > klp-relocations. The solution that led to arch/x86/kernel/livepatch.c > introduces "klp.arch" sections that rename such klp-relocations *and* > their associated special section data structures. Processing is then > deferred until after a relevant klp_object is loaded. Correct. > > I think, we should do the same for jump labels. Add > > jump_label_apply_nops() from module_finalize() to > > arch_klp_init_object_loaded() and convert jump_table ELF section so its > > processing is delayed. > > Nod. Tthat sounds about right. There may be some more work yet in the > static keys API as well, but I'm not 100%. > > > Which leads me another TODO... klp-convert does not convert even > > .altinstructions and .parainstructions sections, so it has that problem as > > well. If I remember, it was on Josh's TODO list when he first introduced > > klp-convert. See cover.1477578530.git.jpoimboe@xxxxxxxxxx. > > In the RFC, Josh highlights a somewhat difficult problem regarding these > special sections -- how to associate these special section data > structures and their relocations to a specific klp_object. > > If I understand his suggestion, he proposed annotating livepatch module > replacement functions as to stuff them into specially named ELF sections > (which would include the klp_object name) and then bypass the existing > livepatch registration API. No minor change. > > With that in mind, I'm starting to think of a game plan for klp-convert > like: > > - phase 1: detect /abort unsupported sections > > - phase 2: manual annotations in livepatch modules (like > KLP_MODULE_RELOC / SYMPOS, but for special sections) so > that klp-convert can start building "klp.arch" sections > > - phase 3: livepatch API change above to support somewhat more > automatic generation of phase 2 annotations Looks good to me. First, I'd focus on something which covers (hopefully) a vast majority cases and then we can do the rest. So yes, this seems to be a good plan. > > And of course we should look at the other supported architectures and > > their module_finalize() functions. I have it on my TODO list somewhere, > > but you know how it works with those :/. I am sure there are more hidden > > surprises there. > > Hmm, well powerpc and s390 do appear to have processing for special > sections as well ... but for the moment, I'm going to focus on x86 as > that seems like enough work for now :) Yes, please :). > > > Detection > > > --------- > > > > > > I can post ("livepatch/klp-convert: abort on static key conversion") > > > here as a follow commit if it looks reasonable and folks wish to review > > > it... or we can try and tackle static keys before merging klp-convert. > > > > Good idea. I'd rather fix it, but I think it could be a lot of work, so > > something like this patch seems to be a good idea. > > I'm thinking of adding this in a commit so klp-convert can intercept > these sections: > > static bool is_section_supported(char *sname) > { > if (strcmp(sname, ".rela.altinstructions") == 0) > return false; > if (strcmp(sname, ".rela.parainstructions") == 0) > return false; > if (strcmp(sname, ".rela__jump_table") == 0) > return false; > return true; > } > > Right now my v4 collection has a bunch of small fixups and nitpick > corrections. It feels like a good resting place for now before > embarking on special section support, what do you think? Yes. Thanks Miroslav