Hi Joe, On Tue, Aug 2, 2022 at 5:31 AM Joe Lawrence <joe.lawrence@xxxxxxxxxx> wrote: > > On 8/1/22 17:19, Song Liu wrote: > > On Mon, Aug 1, 2022 at 3:25 AM Petr Mladek <pmladek@xxxxxxxx> wrote: > >> > >> On Sat 2022-07-30 20:20:22, Song Liu wrote: > >>> On Sat, Jul 30, 2022 at 3:32 PM Song Liu <song@xxxxxxxxxx> wrote: > >>>> > >>>> On Tue, Jul 26, 2022 at 8:54 PM Song Liu <song@xxxxxxxxxx> wrote: > >>>>> > >>>>> On Tue, Jul 26, 2022 at 4:33 PM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > >>>>>> > >>>>>> On Thu, Jul 21, 2022 at 10:51:47AM -0700, Song Liu wrote: > >>>>>>> From: Miroslav Benes <mbenes@xxxxxxx> > >>>>>>> > >>>>>>> Josh reported a bug: > >>>>>>> > >>>>>>> When the object to be patched is a module, and that module is > >>>>>>> rmmod'ed and reloaded, it fails to load with: > >>>>>>> > >>>>>>> module: x86/modules: Skipping invalid relocation target, existing value is nonzero for type 2, loc 00000000ba0302e9, val ffffffffa03e293c > >>>>>>> livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8) > >>>>>>> livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd' > >>>>>>> > >>>>>>> The livepatch module has a relocation which references a symbol > >>>>>>> in the _previous_ loading of nfsd. When apply_relocate_add() > >>>>>>> tries to replace the old relocation with a new one, it sees that > >>>>>>> the previous one is nonzero and it errors out. > >>>>>>> > >>>>>>> On ppc64le, we have a similar issue: > >>>>>>> > >>>>>>> module_64: livepatch_nfsd: Expected nop after call, got e8410018 at e_show+0x60/0x548 [livepatch_nfsd] > >>>>>>> livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8) > >>>>>>> livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd' > >>>>>>> > >>>>>> 3) A selftest would be a good idea. > >>>>> > >>>> > >>>> I found it is pretty tricky to run the selftests inside a qemu VM. How about > >>>> we test it with modules in samples/livepatch? Specifically, we can add a > >>>> script try to reload livepatch-shadow-mod.ko. > >>> > >>> Actually, livepatch-shadow-mod.ko doesn't have the reload problem before > >>> the fix. Is this expected? > >> > >> Good question. I am afraid that there is no easy way to prepare > >> the selftest at the moment. > >> > >> There are two situations when a symbol from the livepatched module is > >> relocated: > >> > >> > >> 1. The livepatch might access a symbol exported by the module via > >> EXPORT_SYMBOL(). In this case, it is "normal" external symbol > >> and it gets relocated by the module loader. > >> > >> But EXPORT_SYMBOL() will create an explicit dependency between the > >> livepatch and livepatched module. As a result, the livepatch > >> module could be loaded only when the livepatched module is loaded. > >> And the livepatched module could not be removed when the livepatch > >> module is loaded. > >> > >> In this case, the problem will not exist. Well, the developers > >> of the livepatch module will probably want to avoid this > >> dependency. > >> > >> > >> 2. The livepatch module might access a non-exported symbol from another > >> module using the special elf section for klp relocation, see > >> section, see Documentation/livepatch/module-elf-format.rst > >> > >> These symbols are relocated in klp_apply_section_relocs(). > >> > >> The problem is that upstream does not have a support to > >> create this elf section. There is a patchset for this, see > >> https://lore.kernel.org/all/20220216163940.228309-1-joe.lawrence@xxxxxxxxxx/ > >> It requires some more review. > >> > >> > >> Resume: I think that we could not prepare the selftest without > >> upstreaming klp-convert tool. > > > > Thanks for the explanation! I suspected the same issue, but couldn't > > connect all the logic. > > > > I guess the selftests can wait until the klp-convert tool. > > > > Hi Song, > > Petr is correct about selftests and these relocations. Let me know if > rebasing the klp-convert patchset would be helpful in your testing. > Otherwise kpatch-build is the only (easy?) way to create klp-relocations > as far as I know. (For limited arches anyway.) I was able to test the patch on x86_64 with kpatch-build. I will look into klp-convert later (after I fix kpatch-build for some OOT modules..) I the meanwhile, I guess this patch doesn't need to wait for klp-convert and the selftest? Thanks, Song
