kernel/linux.git/tools/objtool/klp-diff.c, branch v7.3-rc1

Merge tag 'x86_alternatives_for_v7.3_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2026-08-19T01:11:25+00:00

Pull x86 alternatives update from Borislav Petkov: - Remove the smp_locks alternatives machinery which was used to patch out lock prefixes when running a SMP kernel on a uniprocessor machine * tag 'x86_alternatives_for_v7.3_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/alternative: Drop smp_locks glue

objtool/klp: Fix vmlinux klp relocations for EXPORT_SYMBOL_FOR_MODULES()

2026-08-17T08:53:55+00:00

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., so post-link names the section .klp.rela.., 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 Signed-off-by: Josh Poimboeuf Signed-off-by: Ingo Molnar Acked-by: Song Liu Link: https://patch.msgid.link/f8e3b9fae109903a6aafb2a33310e4afdcebf58e.1786761327.git.jpoimboe@kernel.org Closes: https://lore.kernel.org/CADBMgpz7iWC0=t=_gE-tfvv0mTPq4kg0qQ2zgPH8DVPE6eQ9Kw@mail.gmail.com

objtool/klp: Fix .kcfi_traps special section extraction

2026-08-12T20:52:07+00:00

create_fake_symbols() creates a symbol per entry for special sections. It does so in two steps: first for the sections which have ANNOTATE_DATA_SPECIAL annotations, then for the rest, using entsize or the reloc count to infer the entry size. The second step skips the sections already handled by the first one by looking for a symbol at offset 0. That heuristic is too fuzzy: with Clang and CONFIG_CFI, it misfires on .kcfi_traps because Clang emits a .Ltmp* assembler-local label at the start of the section, so no symbols are created and clone_special_sections() extracts nothing. klp-build still reports SUCCESS, but the livepatch module has no __kcfi_traps section and the traps for the patched functions are lost. Look for the actual fake symbols created by the first step instead. Fixes: da4326573ae8d ("objtool/klp: Fix kCFI trap handling") Reported-by: Joe Lawrence Closes: https://lore.kernel.org/r/akQNqlfFC0T5pcMa@redhat.com Acked-by: Song Liu Link: https://patch.msgid.link/8faaead205b219607b6fc2359ae743be824056eb.1786230311.git.jpoimboe@kernel.org Signed-off-by: Josh Poimboeuf

objtool/klp: Fix line numbers in Module.symvers parse errors

2026-08-11T23:10:58+00:00

read_exports() reports the offending line number when it fails to parse Module.symvers. The counter is initialized to 1 but never incremented, so every error blames line 1 regardless of where the bad line is. Acked-by: Joe Lawrence Acked-by: Song Liu Link: https://patch.msgid.link/133e16bb0c7cb916f10bbfb017eba525449ad1d6.1786138493.git.jpoimboe@kernel.org Signed-off-by: Josh Poimboeuf

objtool/klp: Fix relocations for EXPORT_SYMBOL_FOR_MODULES() symbols

2026-08-11T23:10:51+00:00

EXPORT_SYMBOL_FOR_MODULES() puts a symbol in a "module:" namespace, which the module loader grants access to by matching the importing module's name against that list. klp_reloc_needed() only creates a klp reloc for module-owned exports; a vmlinux export gets a normal reloc. For a vmlinux symbol exported with EXPORT_SYMBOL_FOR_MODULES(), using a normal reloc results in a modpost failure in klp-build: ERROR: modpost: module livepatch-foo uses symbol mpol_shared_policy_lookup from namespace module:kvm, but does not import it. And the modpost error is correct: even with that error removed, the patch module would fail to load: livepatch_foo: module uses symbol (mpol_shared_policy_lookup) from namespace module:kvm, but does not import it. livepatch_foo: Unknown symbol mpol_shared_policy_lookup (err -22) Treat it like an unexported symbol by using a klp reloc. Note this only affects "module:" namespaces. Ordinary namespaced exports continue to work with normal relocs thanks to copy_import_ns(), which propagates the patched object's import_ns tags to the patch module. Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files") Reported-by: Joe Lawrence Link: https://lore.kernel.org/6a6608f4-0a05-4d75-8b7f-edddfac9c5d4@redhat.com Acked-by: Joe Lawrence Acked-by: Song Liu Link: https://patch.msgid.link/fe5a00818e06ec613344d41d5944de054fcd8832.1786138493.git.jpoimboe@kernel.org Signed-off-by: Josh Poimboeuf

objtool/klp: Allow new references to module exports

2026-08-11T23:10:51+00:00

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 Acked-by: Song Liu Acked-by: Joe Lawrence Link: https://patch.msgid.link/e0d725acb4774747f0e271308b4ca33daae2d5db.1786138493.git.jpoimboe@kernel.org Signed-off-by: Josh Poimboeuf

objtool/klp: Don't match local symbols against exports

2026-08-11T23:10:51+00:00

While cloning a reloc, klp diff calls find_export() to determine whether the referenced symbol is exported. That decides whether the reference needs a klp reloc, which object the klp symbol belongs to, and whether the symbol's data needs to be copied into the patch module. But find_export() matches purely on symbol name, so a static function or variable which happens to share its name with an export is mistaken for a reference to that export: - klp_reloc_needed() creates a klp reloc pointing at the exporting module's symbol rather than the local one. For a vmlinux export it skips the klp reloc altogether, leaving a normal reloc which the module loader resolves to the vmlinux symbol. - clone_reloc() treats the symbol as external and clones it without its data, leaving a dangling reference. - validate_special_section_klp_reloc() attributes a static branch or call key to the wrong module, and for a vmlinux export skips the unsupported-key check entirely. Exports are always global, so ignore local symbols in find_export(). Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files") Acked-by: Song Liu Acked-by: Joe Lawrence Link: https://patch.msgid.link/dafc7c017d1f62e2190a20dc84a52fbfc4c70210.1786138493.git.jpoimboe@kernel.org Signed-off-by: Josh Poimboeuf

objtool/klp: Fix cross-module klp relocation section naming

2026-08-11T23:10:51+00:00

A klp relocation section is .klp.rela.., where objname is the object being patched. klp-build wrongly derives objname from where the referenced symbol lives, not where it's referenced. For a cross-module reference like patched can_isotp code calling can.ko's can_rx_unregister(), that gives .klp.rela.can..text rather than .klp.rela.can_isotp..text. Unless the patch happens to patch can.ko as well, the relocation never gets applied and the call goes off into the weeds. Name the intermediate section __klp_relocs. so post-link can read the patched object's name from there. Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files") Reported-by: Joe Lawrence Link: https://lore.kernel.org/20260720145658.1103243-2-joe.lawrence@redhat.com Acked-by: Song Liu Acked-by: Joe Lawrence Link: https://patch.msgid.link/ee93a08f3e55e76ffa67d04e283917ddaa893f09.1786138493.git.jpoimboe@kernel.org Signed-off-by: Josh Poimboeuf

objtool/klp: Ignore replacement offset of empty x86 alternatives

2026-08-11T22:04:57+00:00

An x86 alternative with an empty replacement, e.g. the second entry of ALTERNATIVE_2("orig", "repl", ft1, "", ft2) has a replacementlen of zero. Its replacement offset still gets a relocation, but the label it points at is the end of the previous replacement, which is also the beginning of the *next* alternative's replacement. The value is meaningless; get_alt_entry() already ignores it for that reason. klp diff doesn't ignore it. When such an alternative belongs to a changed function, cloning its relocations drags in the unrelated neighboring replacement, along with everything that replacement references. On an x86 clang/lto build an empty alternative in meminfo_proc_show() pulled in the replacement of an alternative in proc_kcore_init(), silently emitting a klp relocation against init text which has long since been freed by the time the patch is applied. Add arch_alt_ignore_new_reloc() and skip such relocations when cloning. This has to be arch specific: on arm64 a zero-length replacement instead identifies an alternative callback, whose replacement offset points at the callback function and must be preserved. Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files") Acked-by: Song Liu Acked-by: Joe Lawrence Link: https://patch.msgid.link/7a885b70974795c3417f3358869e62aafd4ef783.1786138493.git.jpoimboe@kernel.org Signed-off-by: Josh Poimboeuf

objtool/klp: Fix size of empty special section entries

2026-08-11T22:04:57+00:00

create_fake_symbols() sizes each ANNOTATE_DATA_SPECIAL entry from the offset of the next annotation, falling back to the end of the section for the last entry. But the last entry is detected by a zero size, which also happens for an *empty* entry: ALTERNATIVE(oldinstr, "", ft) still annotates its zero-length replacement, at the same offset as the next entry's annotation. So every empty replacement gets a fake symbol spanning the entire rest of .altinstr_replacement. That's harmless today only because find_symbol_containing() picks the smaller of two overlapping symbols. Track whether a next annotation was found rather than inferring it from the size. A zero-length fake symbol is fine: find_symbol_containing() skips those, so the properly sized symbol at the same offset still wins. Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files") Acked-by: Song Liu Acked-by: Joe Lawrence Link: https://patch.msgid.link/913e691c5009397df832c7c9a18cd5cf71b42737.1786138493.git.jpoimboe@kernel.org Signed-off-by: Josh Poimboeuf