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klp_reloc_needed() returns true for module exports to support late-module patching. However, clone_reloc_klp() unconditionally rejects symbols without a twin (i.e., new references added by the patch), even when the symbol is a known export from Module.symvers. Relax the check: allow new references to exported symbols by only erroring on !twin when there is no export. The export metadata from Module.symvers provides sufficient context to emit the klp-relocation without a twin. For a module export that isn't sufficient on its own though, as the resulting klp relocation will only be resolved at patch-enable time if the exporting module is loaded. If the original (unpatched) module already depends on the exporting module, the dependency is safe: the module loader ensures the dependency is satisfied before the patched module can be loaded, so the klp relocation target will exist. However, if the patch introduces a reference to a module that the original doesn't depend on, there is no such guarantee. The exporting module could be absent or could be unloaded at any time, leading to a relocation failure or use-after-free. So also add a build-time check: when a new symbol reference (no twin) targets a module export, verify that the original module already has at least one UNDEF symbol resolving to that same exporting module. If not, error out with a diagnostic message. Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com> Acked-by: Song Liu <song@kernel.org> Acked-by: Joe Lawrence <joe.lawrence@redhat.com> Link: https://patch.msgid.link/e0d725acb4774747f0e271308b4ca33daae2d5db.1786138493.git.jpoimboe@kernel.org Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> |
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