[PATCH v5 17/22] objtool: Disable CFI warnings

[Sami Tolvanen]

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@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 tools/objtool/check.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e55fdf952a3a..48e18737a2d1 100644
--- 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)
-- 
2.37.2.789.g6183377224-goog