[PATCH v3 12/39] x86/linkage: Add ENDBR to SYM_FUNC_START*()

[Peter Zijlstra]

Ensure the ASM functions have ENDBR on for IBT builds, this follows
the ARM64 example. Unlike ARM64, we'll likely end up overwriting them
with poison.

Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 arch/x86/include/asm/linkage.h |   39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

--- a/arch/x86/include/asm/linkage.h
+++ b/arch/x86/include/asm/linkage.h
@@ -3,6 +3,7 @@
 #define _ASM_X86_LINKAGE_H
 
 #include <linux/stringify.h>
+#include <asm/ibt.h>
 
 #undef notrace
 #define notrace __attribute__((no_instrument_function))
@@ -34,5 +35,43 @@
 
 #endif /* __ASSEMBLY__ */
 
+/*
+ * compressed and purgatory define this to disable EXPORT,
+ * hijack this same to also not emit ENDBR.
+ */
+#ifndef __DISABLE_EXPORTS
+
+/* SYM_FUNC_START -- use for global functions */
+#define SYM_FUNC_START(name)				\
+	SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN)	\
+	ENDBR
+
+/* SYM_FUNC_START_NOALIGN -- use for global functions, w/o alignment */
+#define SYM_FUNC_START_NOALIGN(name)			\
+	SYM_START(name, SYM_L_GLOBAL, SYM_A_NONE)	\
+	ENDBR
+
+/* SYM_FUNC_START_LOCAL -- use for local functions */
+#define SYM_FUNC_START_LOCAL(name)			\
+	SYM_START(name, SYM_L_LOCAL, SYM_A_ALIGN)	\
+	ENDBR
+
+/* SYM_FUNC_START_LOCAL_NOALIGN -- use for local functions, w/o alignment */
+#define SYM_FUNC_START_LOCAL_NOALIGN(name)		\
+	SYM_START(name, SYM_L_LOCAL, SYM_A_NONE)	\
+	ENDBR
+
+/* SYM_FUNC_START_WEAK -- use for weak functions */
+#define SYM_FUNC_START_WEAK(name)			\
+	SYM_START(name, SYM_L_WEAK, SYM_A_ALIGN)	\
+	ENDBR
+
+/* SYM_FUNC_START_WEAK_NOALIGN -- use for weak functions, w/o alignment */
+#define SYM_FUNC_START_WEAK_NOALIGN(name)		\
+	SYM_START(name, SYM_L_WEAK, SYM_A_NONE)		\
+	ENDBR
+
+#endif /* __DISABLE_EXPORTS */
+
 #endif /* _ASM_X86_LINKAGE_H */