linux-kernel - [PATCH v2 15/20] x86/ftrace: Support objtool vmlinux.o validation in ftrace

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Date:   Thu, 21 Jan 2021 15:29:31 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com,
        Miroslav Benes <mbenes@...e.cz>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH v2 15/20] x86/ftrace: Support objtool vmlinux.o validation in ftrace_64.S

With objtool vmlinux.o validation of return_to_handler(), now that
objtool has visibility inside the retpoline, jumping from EMPTY state to
a proper function state results in a stack state mismatch.

return_to_handler() is actually quite normal despite the underlying
magic.  Just annotate it as a normal function.

Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/kernel/ftrace_64.S | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 1bf568d901b1..7c273846c687 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -334,8 +334,7 @@ SYM_FUNC_START(ftrace_graph_caller)
 	retq
 SYM_FUNC_END(ftrace_graph_caller)
 
-SYM_CODE_START(return_to_handler)
-	UNWIND_HINT_EMPTY
+SYM_FUNC_START(return_to_handler)
 	subq  $24, %rsp
 
 	/* Save the return values */
@@ -350,5 +349,5 @@ SYM_CODE_START(return_to_handler)
 	movq (%rsp), %rax
 	addq $24, %rsp
 	JMP_NOSPEC rdi
-SYM_CODE_END(return_to_handler)
+SYM_FUNC_END(return_to_handler)
 #endif
-- 
2.29.2