Commit 3c68a92d authored Sep 08, 2022 by Sami Tolvanen Committed by Kees Cook Sep 26, 2022

objtool: Disable CFI warnings



The __cfi_ preambles contain a mov instruction that embeds the KCFI
type identifier in the following format:

  ; type preamble
  __cfi_function:
    mov <id>, %eax
  function:
    ...

While the preamble symbols are STT_FUNC and contain valid
instructions, they are never executed and always fall through. Skip
the warning for them.

.kcfi_traps sections point to CFI traps in text sections. Also skip
the warning about them referencing !ENDBR instructions.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220908215504.3686827-18-samitolvanen@google.com

parent 5141d3a0

tools/objtool/check.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -3316,6 +3316,10 @@ static int validate_branch(struct objtool_file file, struct symbol func,
		next_insn = next_insn_to_validate(file, insn);

		if (func && insn->func && func != insn->func->pfunc) {
		/* Ignore KCFI type preambles, which always fall through */
		if (!strncmp(func->name, "__cfi_", 6))
		return 0;

		WARN("%s() falls through to next function %s()",
		func->name, insn->func->name);
		return 1;
		@@ -4113,7 +4117,8 @@ static int validate_ibt(struct objtool_file *file)
		!strcmp(sec->name, "__bug_table") \|\|
		!strcmp(sec->name, "__ex_table") \|\|
		!strcmp(sec->name, "__jump_table") \|\|
		!strcmp(sec->name, "__mcount_loc"))
		!strcmp(sec->name, "__mcount_loc") \|\|
		!strcmp(sec->name, ".kcfi_traps"))
		continue;

		list_for_each_entry(reloc, &sec->reloc->reloc_list, list)