x86/kprobes: enable EXECMEM_ROX_CACHE for kprobes allocations

x86::alloc_insn_page() always allocates ROX memory.

Instead of overriding this method, add EXECMEM_KPROBES entry in
execmem_info with pgprot set to PAGE_KERNEL_ROX and use ROX cache when
configuration and CPU features allow it.

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

arch/x86/kernel/kprobes/core.c

···
 	return len;
 }
 
-/* Make page to RO mode when allocate it */
-void *alloc_insn_page(void)
-{
-	void *page;
-
-	page = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
-	if (!page)
-		return NULL;
-
-	/*
-	 * TODO: Once additional kernel code protection mechanisms are set, ensure
-	 * that the page was not maliciously altered and it is still zeroed.
-	 */
-	set_memory_rox((unsigned long)page, 1);
-
-	return page;
-}
-
 /* Kprobe x86 instruction emulation - only regs->ip or IF flag modifiers */
 
 static void kprobe_emulate_ifmodifiers(struct kprobe *p, struct pt_regs *regs)

arch/x86/mm/init.c

···
 				.pgprot	= pgprot,
 				.alignment = MODULE_ALIGN,
 			},
-			[EXECMEM_KPROBES ... EXECMEM_BPF] = {
+			[EXECMEM_KPROBES] = {
+				.flags	= flags,
+				.start	= start,
+				.end	= MODULES_END,
+				.pgprot	= PAGE_KERNEL_ROX,
+				.alignment = MODULE_ALIGN,
+			},
+			[EXECMEM_FTRACE ... EXECMEM_BPF] = {
 				.flags	= EXECMEM_KASAN_SHADOW,
 				.start	= start,
 				.end	= MODULES_END,