Re: [PATCH] objtool/klp: Fix vmlinux klp relocations for EXPORT_SYMBOL_FOR_MODULES()

On Fri, Aug 14, 2026 at 7:36 PM Josh Poimboeuf <[email protected]> wrote:
>
> When a module function references a vmlinux symbol which is exported
> with EXPORT_SYMBOL_FOR_MODULES(), a patch to that function needs to use
> a klp reloc.
>
> Currently, livepatch fails to load such a module:
>
>   livepatch: invalid access to vmlinux symbol 'get_task_policy' from module-specific livepatch relocation section
>   livepatch: failed to initialize patch 'livepatch_test' for module 'testmod' (-22)
>   livepatch: patch 'livepatch_test' failed for module 'testmod', refusing to load module 'testmod'
>
> klp diff puts all klp relocs in __klp_relocs.<patched object>, so
> post-link names the section .klp.rela.<patched object>.<secname>, which the
> kernel rejects for vmlinux symbols.
>
> Commit 07f14d6af9d77 ("objtool/klp: Fix cross-module klp relocation
> section naming") changed the meaning of objname in the klp rela section
> name to be where the referenced symbol is referenced rather than where
> it lives.  That premise only holds for symbols in a module: the relocs
> get applied when the patched module gets patched, and the module
> dependency guarantees the referenced module is loaded by then.
>
> A vmlinux symbol needs the opposite.  It's always resolvable, and it has
> to be applied when the patch module loads, before the module loader
> initializes the patch module's special sections, which may reference it.
> That's why livepatch rejects vmlinux symbols in module-specific
> sections.
>
> Use "vmlinux" as the section objname when the referenced symbol lives in
> vmlinux.  This moves such klp relocs from .klp.rela.kvm..text to
> .klp.rela.vmlinux..text.
>
> Fixes: 07f14d6af9d77 ("objtool/klp: Fix cross-module klp relocation section naming")
> Reported-by: Dylan Hatch <[email protected]>
> Closes: https://lore.kernel.org/CADBMgpz7iWC0=t=_gE-tfvv0mTPq4kg0qQ2zgPH8DVPE6eQ9Kw@mail.gmail.com
> Signed-off-by: Josh Poimboeuf <[email protected]>

Acked-by: Song Liu <[email protected]>