arm64: mm: Mark .rodata as RO

Currently the .rodata section is actually still executable when DEBUG_RODATA
is enabled. This changes that so the .rodata is actually read only, no execute.
It also adds the .rodata section to the mem_init banner.
Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
[catalin.marinas@arm.com: added vm_struct vmlinux_rodata in map_kernel()]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/vmlinux.lds.S

@@ -114,8 +114,9 @@ SECTIONS
 		*(.got)			/* Global offset table		*/
 	}
 
-	RO_DATA(PAGE_SIZE)
-	EXCEPTION_TABLE(8)
+	ALIGN_DEBUG_RO_MIN(PAGE_SIZE)
+	RO_DATA(PAGE_SIZE)		/* everything from this point to */
+	EXCEPTION_TABLE(8)		/* _etext will be marked RO NX   */
 	NOTES
 
 	ALIGN_DEBUG_RO_MIN(PAGE_SIZE)

arch/arm64/mm/init.c

@@ -363,6 +363,7 @@ void __init mem_init(void)
 		  "    vmalloc : 0x%16lx - 0x%16lx   (%6ld GB)\n"
 		  "      .init : 0x%p" " - 0x%p" "   (%6ld KB)\n"
 		  "      .text : 0x%p" " - 0x%p" "   (%6ld KB)\n"
+		  "    .rodata : 0x%p" " - 0x%p" "   (%6ld KB)\n"
 		  "      .data : 0x%p" " - 0x%p" "   (%6ld KB)\n"
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 		  "    vmemmap : 0x%16lx - 0x%16lx   (%6ld GB maximum)\n"
@@ -377,7 +378,8 @@ void __init mem_init(void)
 		  MLM(MODULES_VADDR, MODULES_END),
 		  MLG(VMALLOC_START, VMALLOC_END),
 		  MLK_ROUNDUP(__init_begin, __init_end),
-		  MLK_ROUNDUP(_text, _etext),
+		  MLK_ROUNDUP(_text, __start_rodata),
+		  MLK_ROUNDUP(__start_rodata, _etext),
 		  MLK_ROUNDUP(_sdata, _edata),
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 		  MLG((unsigned long)vmemmap,

arch/arm64/mm/mmu.c

@@ -449,12 +449,18 @@ static void __init map_mem(pgd_t *pgd)
 
 void mark_rodata_ro(void)
 {
-	if (!IS_ENABLED(CONFIG_DEBUG_RODATA))
-		return;
+	unsigned long section_size;
 
+	section_size = (unsigned long)__start_rodata - (unsigned long)_stext;
 	create_mapping_late(__pa(_stext), (unsigned long)_stext,
-				(unsigned long)_etext - (unsigned long)_stext,
-				PAGE_KERNEL_ROX);
+			    section_size, PAGE_KERNEL_ROX);
+	/*
+	 * mark .rodata as read only. Use _etext rather than __end_rodata to
+	 * cover NOTES and EXCEPTION_TABLE.
+	 */
+	section_size = (unsigned long)_etext - (unsigned long)__start_rodata;
+	create_mapping_late(__pa(__start_rodata), (unsigned long)__start_rodata,
+			    section_size, PAGE_KERNEL_RO);
 }
 
 void fixup_init(void)
@@ -493,9 +499,10 @@ static void __init map_kernel_chunk(pgd_t *pgd, void *va_start, void *va_end,
  */
 static void __init map_kernel(pgd_t *pgd)
 {
-	static struct vm_struct vmlinux_text, vmlinux_init, vmlinux_data;
+	static struct vm_struct vmlinux_text, vmlinux_rodata, vmlinux_init, vmlinux_data;
 
-	map_kernel_chunk(pgd, _stext, _etext, PAGE_KERNEL_EXEC, &vmlinux_text);
+	map_kernel_chunk(pgd, _stext, __start_rodata, PAGE_KERNEL_EXEC, &vmlinux_text);
+	map_kernel_chunk(pgd, __start_rodata, _etext, PAGE_KERNEL, &vmlinux_rodata);
 	map_kernel_chunk(pgd, __init_begin, __init_end, PAGE_KERNEL_EXEC,
 			 &vmlinux_init);
 	map_kernel_chunk(pgd, _data, _end, PAGE_KERNEL, &vmlinux_data);