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Date:   Fri, 10 Jun 2022 16:35:08 -0700
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Subject: [RFC PATCH v3 15/20] objtool: Disable CFI warnings
From:   Sami Tolvanen <samitolvanen@google.com>
To:     linux-kernel@vger.kernel.org
Cc:     Kees Cook <keescook@chromium.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Joao Moreira <joao@overdrivepizza.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        linux-hardening@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev,
        Sami Tolvanen <samitolvanen@google.com>
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Precedence: bulk

The __cfi_ preambles contain int3 padding and a mov instruction that
embeds the KCFI type identifier in the following format:

  ; type preamble
  __cfi_function:
    int3
    int3
    mov <id>, %eax
    int3
    int3
  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>
---
 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 864bb9dd3584..337b92c3b755 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3207,6 +3207,10 @@ 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;
@@ -3827,7 +3831,8 @@ static int validate_ibt(struct objtool_file *file)
 		    !strcmp(sec->name, "__ex_table")			||
 		    !strcmp(sec->name, "__jump_table")			||
 		    !strcmp(sec->name, "__mcount_loc")			||
-		    !strcmp(sec->name, "__tracepoints"))
+		    !strcmp(sec->name, "__tracepoints")			||
+		    !strcmp(sec->name, ".kcfi_traps"))
 			continue;
 
 		list_for_each_entry(reloc, &sec->reloc->reloc_list, list)
-- 
2.36.1.476.g0c4daa206d-goog