arm64: dump: Add checking for writable and exectuable pages

Page mappings with full RWX permissions are a security risk. x86
has an option to walk the page tables and dump any bad pages.
(See e1a58320a3 ("x86/mm: Warn on W^X mappings")). Add a similar
implementation for arm64.

Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Laura Abbott <labbott@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
[catalin.marinas@arm.com: folded fix for KASan out of bounds from Mark Rutland]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/mmu.c

@@ -40,6 +40,7 @@
 #include <asm/tlb.h>
 #include <asm/memblock.h>
 #include <asm/mmu_context.h>
+#include <asm/ptdump.h>
 
 u64 idmap_t0sz = TCR_T0SZ(VA_BITS);
 
@@ -438,6 +439,8 @@ void mark_rodata_ro(void)
 
 	/* flush the TLBs after updating live kernel mappings */
 	flush_tlb_all();
+
+	debug_checkwx();
 }
 
 static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end,