CFI: Move function_nocfi() into compiler.h

Currently the common definition of function_nocfi() is provided by
<linux/mm.h>, and architectures are expected to provide a definition in
<asm/memory.h>. Due to header dependencies, this can make it hard to use
function_nocfi() in low-level headers.

As function_nocfi() has no dependency on any mm code, nor on any memory
definitions, it doesn't need to live in <linux/mm.h> or <asm/memory.h>.
Generally, it would make more sense for it to live in
<linux/compiler.h>, where an architecture can override it in
<asm/compiler.h>.

Move the definitions accordingly.

Signed-off-by: Mark Rutland <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Sami Tolvanen <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index df5b405e6305..099e529a5d25 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -213,6 +213,16 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 	__v;								\
 })
 
+/*
+ * With CONFIG_CFI_CLANG, the compiler replaces function addresses in
+ * instrumented C code with jump table addresses. Architectures that
+ * support CFI can define this macro to return the actual function address
+ * when needed.
+ */
+#ifndef function_nocfi
+#define function_nocfi(x) (x)
+#endif
+
 #endif /* __KERNEL__ */
 
 /*