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

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e55fdf952a3a15c2af189315c90f102e0bf6c8df..48e18737a2d1850554493b950b35828855978fb3 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -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)