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.
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| @@ -1295,6 +1295,28 @@ static int convert_reloc_sym(struct elf *elf, struct reloc *reloc) · 1294 unmodified lines | |||
| 1295 | return convert_reloc_secsym_to_sym(elf, reloc); | 1295 | return convert_reloc_secsym_to_sym(elf, reloc); |
| 1296 | } | 1296 | } |
| 1297 | 1297 | ||
| 1298 | /* | ||
| 1299 | * Check if the original module already has a dependency on dep_mod, i.e. it | ||
| 1300 | * already references at least one export from that module. | ||
| 1301 | */ | ||
| 1302 | static bool has_module_dep(struct elfs *e, const char *dep_mod) | ||
| 1303 | { | ||
| 1304 | struct symbol *sym; | ||
| 1305 | |||
| 1306 | for_each_sym(e->orig, sym) { | ||
| 1307 | struct export *exp; | ||
| 1308 | |||
| 1309 | if (!is_undef_sym(sym) || is_weak_sym(sym)) | ||
| 1310 | continue; | ||
| 1311 | |||
| 1312 | exp = find_export(sym); | ||
| 1313 | if (exp && !strcmp(exp->mod, dep_mod)) | ||
| 1314 | return true; | ||
| 1315 | } | ||
| 1316 | |||
| 1317 | return false; | ||
| 1318 | } | ||
| 1319 | |||
| 1298 | /* | 1320 | /* |
| 1299 | * Convert a regular relocation to a klp relocation (sort of). | 1321 | * Convert a regular relocation to a klp relocation (sort of). |
| 1300 | */ | 1322 | */ |
| @@ -1314,8 +1336,17 @@ static int clone_reloc_klp(struct elfs *e, struct reloc *patched_reloc, · 13 unmodified lines | |||
| 1314 | unsigned long sympos; | 1336 | unsigned long sympos; |
| 1315 | 1337 | ||
| 1316 | if (!patched_sym->twin) { | 1338 | if (!patched_sym->twin) { |
| 1317 | ERROR("unexpected klp reloc for new symbol %s", patched_sym->name); | 1339 | if (!export) { |
| 1318 | return -1; | 1340 | ERROR("unexpected klp reloc for new symbol %s", patched_sym->name); |
| 1341 | return -1; | ||
| 1342 | } | ||
| 1343 | |||
| 1344 | if (strcmp(export->mod, "vmlinux") && | ||
| 1345 | !has_module_dep(e, export->mod)) { | ||
| 1346 | ERROR("%s: new reference to %s (exported by %s) would create an undeclared module dependency", | ||
| 1347 | patched_sym->name, export->sym, export->mod); | ||
| 1348 | return -1; | ||
| 1349 | } | ||
| 1319 | } | 1350 | } |
| 1320 | 1351 | ||
| 1321 | /* | 1352 | /* |