x86/ftrace: enable EXECMEM_ROX_CACHE for ftrace allocations

For the most part ftrace uses text poking and can handle ROX memory.  The
only place that requires writable memory is create_trampoline() that
updates the allocated memory and in the end makes it ROX.

Use execmem_alloc_rw() in x86::ftrace::alloc_tramp() and enable ROX cache
for EXECMEM_FTRACE when configuration and CPU features allow that.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Mike Rapoport (Microsoft) <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Steven Rostedt (Google) <[email protected]>
Cc: Daniel Gomez <[email protected]>
Cc: Masami Hiramatsu (Google) <[email protected]>
Cc: Petr Pavlu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: rppt

arch/x86/kernel/ftrace.c

@@ -263,7 +263,7 @@ void arch_ftrace_update_code(int command)
 
 static inline void *alloc_tramp(unsigned long size)
 {
-	return execmem_alloc(EXECMEM_FTRACE, size);
+	return execmem_alloc_rw(EXECMEM_FTRACE, size);
 }
 static inline void tramp_free(void *tramp)
 {

arch/x86/mm/init.c

@@ -1105,7 +1105,14 @@ struct execmem_info __init *execmem_arch_setup(void)
 				.pgprot	= PAGE_KERNEL_ROX,
 				.alignment = MODULE_ALIGN,
 			},
-			[EXECMEM_FTRACE ... EXECMEM_BPF] = {
+			[EXECMEM_FTRACE] = {
+				.flags	= flags,
+				.start	= start,
+				.end	= MODULES_END,
+				.pgprot	= pgprot,
+				.alignment = MODULE_ALIGN,
+			},
+			[EXECMEM_BPF] = {
 				.flags	= EXECMEM_KASAN_SHADOW,
 				.start	= start,
 				.end	= MODULES_END,