[RFC PATCH 2/2] x86: Add asm frame pointer setup macros

[Josh Poimboeuf]

Add some helper macros for asm functions so that they can comply with
stackvalidate.

The FUNC_ENTER and FUNC_RETURN macros help asm functions save, set up,
and restore frame pointers.

The RET_NOVALIDATE and FILE_NOVALIDATE macros can be used to whitelist
the few locations which need a return instruction outside of a callable
function.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 arch/x86/include/asm/func.h | 82 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)
 create mode 100644 arch/x86/include/asm/func.h

diff --git a/arch/x86/include/asm/func.h b/arch/x86/include/asm/func.h
new file mode 100644
index 0000000..ae84196
--- /dev/null
+++ b/arch/x86/include/asm/func.h
@@ -0,0 +1,82 @@
+#ifndef _ASM_X86_FUNC_H
+#define _ASM_X86_FUNC_H
+
+#include <linux/linkage.h>
+#include <asm/dwarf2.h>
+#include <asm/asm.h>
+
+.macro FUNC_ENTER_NO_FP name
+	ENTRY(\name)
+	CFI_STARTPROC
+	CFI_DEF_CFA _ASM_SP, __ASM_SEL(4, 8)
+.endm
+
+.macro FUNC_RETURN_NO_FP name
+	CFI_DEF_CFA _ASM_SP, __ASM_SEL(4, 8)
+	__ASM_SIZE(ret)
+	CFI_ENDPROC
+	ENDPROC(\name)
+.endm
+
+#ifdef CONFIG_FRAME_POINTER
+
+.macro FUNC_ENTER_FP name
+	FUNC_ENTER_NO_FP \name
+	__ASM_SIZE(push, _cfi) %_ASM_BP
+	CFI_REL_OFFSET _ASM_BP, 0
+	_ASM_MOV %_ASM_SP, %_ASM_BP
+	CFI_DEF_CFA_REGISTER _ASM_BP
+.endm
+
+.macro FUNC_RETURN_FP name
+	__ASM_SIZE(pop, _cfi) %_ASM_BP
+	CFI_RESTORE _ASM_BP
+	FUNC_RETURN_NO_FP \name
+.endm
+
+/*
+ * Every callable asm function should be bookended with FUNC_ENTER and
+ * FUNC_RETURN.  They do proper frame pointer and DWARF CFI setups in order to
+ * achieve more reliable stack traces.
+ *
+ * For the sake of simplicity and correct DWARF annotations, use of the macros
+ * requires that the return instruction comes at the end of the function.
+ */
+#define FUNC_ENTER(name) FUNC_ENTER_FP name
+#define FUNC_RETURN(name) FUNC_RETURN_FP name
+
+/*
+ * RET_NOVALIDATE tells the stack validation script to whitelist the return
+ * instruction immediately after the macro.  Only use it if you're completely
+ * sure you need a return instruction outside of a callable function.
+ * Otherwise, if the code can be called and you haven't annotated it with
+ * FUNC_ENTER/FUNC_RETURN, it will break stack trace reliability.
+ */
+.macro RET_NOVALIDATE
+	163:
+	.pushsection __stackvalidate_whitelist_ret, "ae"
+	_ASM_ALIGN
+	.long 163b - .
+	.popsection
+.endm
+
+/*
+ * FILE_NOVALIDATE is like RET_NOVALIDATE except it whitelists the entire file.
+ * Use with extreme caution or you will silently break stack traces.
+ */
+.macro FILE_NOVALIDATE
+	.pushsection __stackvalidate_whitelist_file, "ae"
+	.long 0
+	.popsection
+.endm
+
+#else /* !FRAME_POINTER */
+
+#define FUNC_ENTER(name) FUNC_ENTER_NO_FP name
+#define FUNC_RETURN(name) FUNC_RETURN_NO_FP name
+#define RET_NOVALIDATE
+#define FILE_NOVALIDATE
+
+#endif /* FRAME_POINTER */
+
+#endif /* _ASM_X86_FUNC_H */
-- 
2.1.0

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