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objtool: Disable CFI warnings

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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
This commit is contained in:
Sami Tolvanen 2022-09-08 14:54:59 -07:00 committed by Kees Cook
parent 5141d3a06b
commit 3c68a92d17
1 changed files with 6 additions and 1 deletions
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7
tools/objtool/check.c
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@ -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)