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

Peter Zijlstra
2022-03-03T11:30:33Z

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@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
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 */