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Thu, 10 Sep 2026 01:52:47 -0700 (PDT) From: Longjun Luo To: jpoimboe@kernel.org, peterz@infradead.org Cc: song@kernel.org, jikos@kernel.org, pmladek@suse.com, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, Longjun Luo Subject: [PATCH] objtool/klp: Fix missed changes to same-named symbol references Date: Thu, 10 Sep 2026 16:52:18 +0800 Message-ID: <20260910085218.66565-1-luolongjuna@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: live-patching@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hashing symbol references by demangled_name alone can miss target changes while the instruction or data bytes and normalized relocation offsets remain unchanged. This occurs when: - A global function moves between files and calls a same-named static function with a different implementation. - A function's call target changes from a global function to a same-named static function, without moving the caller. - A data object, such as an ops structure, changes its function pointer from a global function to a same-named static function. These false negatives can silently omit changed functions from a livepatch or fail to reject changed data. Hash referenced symbols as (filename, demangled_name) instead. Use an empty filename when no FILE is associated, and include both terminating NULs to delimit the fields. Verified all three cases with klp-build on x86-64: the function cases produce livepatch modules with the expected target relocations, and the data case is rejected. Hand-built unchanged-input controls produce identical checksums. Module loading was not tested. Fixes: 0d83da43b1e1 ("objtool/klp: Add --checksum option to generate per-function checksums") Assisted-by: LLM Signed-off-by: Longjun Luo --- tools/objtool/include/objtool/checksum.h | 27 ++++++++++++++++++++++++ tools/objtool/klp-checksum.c | 13 ++++-------- 2 files changed, 31 insertions(+), 9 deletions(-) diff --git a/tools/objtool/include/objtool/checksum.h b/tools/objtool/include/objtool/checksum.h index d46293f54716..1834d34dfd47 100644 --- a/tools/objtool/include/objtool/checksum.h +++ b/tools/objtool/include/objtool/checksum.h @@ -20,6 +20,16 @@ static inline void __checksum_update(struct symbol *sym, const void *data, XXH3_64bits_update(sym->csum.state, data, size); } +/* Include FILE identity to distinguish same-named local targets. */ +static inline void __checksum_update_symbol_identity(struct symbol *sym, + struct symbol *target) +{ + const char *file_name = target->file ? target->file->name : ""; + + __checksum_update(sym, file_name, strlen(file_name) + 1); + __checksum_update(sym, target->demangled_name, strlen(target->demangled_name) + 1); +} + static inline void __checksum_update_insn(struct symbol *sym, struct instruction *insn, const void *data, size_t size) @@ -28,6 +38,14 @@ static inline void __checksum_update_insn(struct symbol *sym, dbg_checksum_insn(sym, insn, XXH3_64bits_digest(sym->csum.state)); } +static inline void __checksum_update_symbol(struct symbol *sym, + struct instruction *insn, + struct symbol *target) +{ + __checksum_update_symbol_identity(sym, target); + dbg_checksum_insn(sym, insn, XXH3_64bits_digest(sym->csum.state)); +} + static inline void __checksum_update_object(struct symbol *sym, unsigned long offset, const char *what, const void *data, @@ -38,6 +56,15 @@ static inline void __checksum_update_object(struct symbol *sym, dbg_checksum_object(sym, offset, what, XXH3_64bits_digest(sym->csum.state)); } +static inline void __checksum_update_object_symbol(struct symbol *sym, + unsigned long offset, + struct symbol *target) +{ + __checksum_update(sym, &offset, sizeof(offset)); + __checksum_update_symbol_identity(sym, target); + dbg_checksum_object(sym, offset, "reloc name", XXH3_64bits_digest(sym->csum.state)); +} + static inline void checksum_finish(struct symbol *sym) { if (sym && sym->csum.state) { diff --git a/tools/objtool/klp-checksum.c b/tools/objtool/klp-checksum.c index b8e47f28997e..3da3fe11bf76 100644 --- a/tools/objtool/klp-checksum.c +++ b/tools/objtool/klp-checksum.c @@ -85,8 +85,7 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func, __checksum_update_insn(func, insn, buf, len); if (call_dest) { - __checksum_update_insn(func, insn, call_dest->demangled_name, - strlen(call_dest->demangled_name)); + __checksum_update_symbol(func, insn, call_dest); } else if (jump_dest) { struct symbol *dest_sym; @@ -102,8 +101,7 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func, if (!dest_sym) goto alts; - __checksum_update_insn(func, insn, dest_sym->demangled_name, - strlen(dest_sym->demangled_name)); + __checksum_update_symbol(func, insn, dest_sym); offset = jump_dest->offset - dest_sym->offset; __checksum_update_insn(func, insn, &offset, sizeof(offset)); @@ -137,8 +135,7 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func, offset -= sym->offset; } - __checksum_update_insn(func, insn, sym->demangled_name, - strlen(sym->demangled_name)); + __checksum_update_symbol(func, insn, sym); __checksum_update_insn(func, insn, &offset, sizeof(offset)); alts: @@ -206,9 +203,7 @@ static void checksum_update_object(struct objtool_file *file, struct symbol *sym offset -= target->offset; } - __checksum_update_object(sym, sym_offset, "reloc name", - target->demangled_name, - strlen(target->demangled_name)); + __checksum_update_object_symbol(sym, sym_offset, target); __checksum_update_object(sym, sym_offset, "reloc addend", &offset, sizeof(offset)); } base-commit: 50d05c7c76c96b90462f24debacca971d2e86713 -- 2.43.7