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.) Thanks, -- Joe
