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. Thanks, Song
