linux-kernel - [PATCH 18/29] x86/ibt,ftrace: Annotate ftrace code patching

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Date:   Fri, 18 Feb 2022 17:49:20 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        jpoimboe@...hat.com, andrew.cooper3@...rix.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com
Subject: [PATCH 18/29] x86/ibt,ftrace: Annotate ftrace code patching

Notably the noinline is required to generate sane code; without it GCC
think's it's awesome to fold in a constant to the code reloc which
puts it in the wrong place to match with the ANNOTATE_NOENDBR.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/kernel/ftrace.c    |    2 +-
 arch/x86/kernel/ftrace_64.S |    9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -69,7 +69,7 @@ static const char *ftrace_nop_replace(vo
 	return x86_nops[5];
 }
 
-static const char *ftrace_call_replace(unsigned long ip, unsigned long addr)
+static noinline const char *ftrace_call_replace(unsigned long ip, unsigned long addr)
 {
 	return text_gen_insn(CALL_INSN_OPCODE, (void *)ip, (void *)addr);
 }
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -145,6 +145,7 @@ SYM_FUNC_START(ftrace_caller)
 	movq %rcx, RSP(%rsp)
 
 SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL)
+	ANNOTATE_NOENDBR
 	/* Load the ftrace_ops into the 3rd parameter */
 	movq function_trace_op(%rip), %rdx
 
@@ -155,6 +156,7 @@ SYM_INNER_LABEL(ftrace_caller_op_ptr, SY
 	movq $0, CS(%rsp)
 
 SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
+	ANNOTATE_NOENDBR
 	call ftrace_stub
 
 	/* Handlers can change the RIP */
@@ -169,6 +171,7 @@ SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBA
 	 * layout here.
 	 */
 SYM_INNER_LABEL(ftrace_caller_end, SYM_L_GLOBAL)
+	ANNOTATE_NOENDBR
 
 	jmp ftrace_epilogue
 SYM_FUNC_END(ftrace_caller);
@@ -179,6 +182,7 @@ SYM_FUNC_START(ftrace_epilogue)
  * It is also used to copy the RET for trampolines.
  */
 SYM_INNER_LABEL_ALIGN(ftrace_stub, SYM_L_WEAK)
+	ANNOTATE_NOENDBR
 	UNWIND_HINT_FUNC
 	RET
 SYM_FUNC_END(ftrace_epilogue)
@@ -192,6 +196,7 @@ SYM_FUNC_START(ftrace_regs_caller)
 	/* save_mcount_regs fills in first two parameters */
 
 SYM_INNER_LABEL(ftrace_regs_caller_op_ptr, SYM_L_GLOBAL)
+	ANNOTATE_NOENDBR
 	/* Load the ftrace_ops into the 3rd parameter */
 	movq function_trace_op(%rip), %rdx
 
@@ -221,6 +226,7 @@ SYM_INNER_LABEL(ftrace_regs_caller_op_pt
 	leaq (%rsp), %rcx
 
 SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
+	ANNOTATE_NOENDBR
 	call ftrace_stub
 
 	/* Copy flags back to SS, to restore them */
@@ -248,6 +254,7 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_
 	 */
 	testq	%rax, %rax
 SYM_INNER_LABEL(ftrace_regs_caller_jmp, SYM_L_GLOBAL)
+	ANNOTATE_NOENDBR
 	jnz	1f
 
 	restore_mcount_regs
@@ -261,6 +268,7 @@ SYM_INNER_LABEL(ftrace_regs_caller_jmp,
 	 * to the return.
 	 */
 SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
+	ANNOTATE_NOENDBR
 	jmp ftrace_epilogue
 
 	/* Swap the flags with orig_rax */
@@ -284,6 +292,7 @@ SYM_FUNC_START(__fentry__)
 	jnz trace
 
 SYM_INNER_LABEL(ftrace_stub, SYM_L_GLOBAL)
+	ANNOTATE_NOENDBR
 	RET
 
 trace: