On Thu, Sep 05, 2019 at 02:45:12PM +0200, Miroslav Benes wrote: > 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' > > He also proposed three different solutions. We could remove the error > check in apply_relocate_add() introduced by commit eda9cec4c9a1 > ("x86/module: Detect and skip invalid relocations"). However the check > is useful for detecting corrupted modules. > > We could also deny the patched modules to be removed. If it proved to be > a major drawback for users, we could still implement a different > approach. The solution would also complicate the existing code a lot. > > We thus decided to reverse the relocation patching (clear all relocation > targets on x86_64, or return back nops on powerpc). The solution is not > universal and is too much arch-specific, but it may prove to be simpler > in the end. > > Reported-by: Josh Poimboeuf <jpoim...@redhat.com> > Signed-off-by: Miroslav Benes <mbe...@suse.cz>
Since we decided to fix late module patching at LPC, the commit message and clear_relocate_add() should both probably clarify that these functions are hacks which are relatively temporary, until we fix the root cause. But this patch gives me a bad feeling :-/ Not that I have a better idea. Has anybody seen this problem in the real world? If not, maybe we'd be better off just pretending the problem doesn't exist for now. -- Josh