BACKPORT: 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>

Bug: 31374226
Change-Id: I6fd95beaf814fc91805da12c5329a57ce9008fd7
(cherry picked from commit 2f39b5f91eb4bccd786d194e70db1dccad784755)
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

3 files changed, 21 insertions, 12 deletions

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 87fd0556a1bd..f1d6c49dcc5f 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -114,14 +114,14 @@ SECTIONS
 		*(.got)			/* Global offset table		*/
 	}
 
+	ALIGN_DEBUG_RO_MIN(PAGE_SIZE)
 	_etext = .;			/* End of text section */
 
-	RO_DATA(PAGE_SIZE)
-	EXCEPTION_TABLE(8)
+	RO_DATA(PAGE_SIZE)		/* everything from this point to     */
+	EXCEPTION_TABLE(8)		/* __init_begin will be marked RO NX */
 	NOTES
 
 	ALIGN_DEBUG_RO_MIN(PAGE_SIZE)
-	_etext = .;			/* End of text and rodata section */
 	__init_begin = .;
 
 	INIT_TEXT_SECTION(8)
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 0db12e9e8765..678878077996 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -376,6 +376,7 @@ 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"
@@ -391,6 +392,7 @@ void __init mem_init(void)
 		  MLG(VMALLOC_START, VMALLOC_END),
 		  MLK_ROUNDUP(__init_begin, __init_end),
 		  MLK_ROUNDUP(_text, _etext),
+		  MLK_ROUNDUP(__start_rodata, __init_begin),
 		  MLK_ROUNDUP(_sdata, _edata),
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 		  MLG(VMEMMAP_START,
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 9dafcfde7c26..4b38f6b8806e 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -386,14 +386,14 @@ static void create_mapping_late(phys_addr_t phys, unsigned long virt,
 static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end)
 {
 	unsigned long kernel_start = __pa(_stext);
-	unsigned long kernel_end = __pa(_etext);
+	unsigned long kernel_end = __pa(__init_begin);
 
 	/*
 	 * Take care not to create a writable alias for the
 	 * read-only text and rodata sections of the kernel image.
 	 */
 
-	/* No overlap with the kernel text */
+	/* No overlap with the kernel text/rodata */
 	if (end < kernel_start || start >= kernel_end) {
 		__create_pgd_mapping(pgd, start, __phys_to_virt(start),
 				     end - start, PAGE_KERNEL,
@@ -402,7 +402,7 @@ static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end
 	}
 
 	/*
-	 * This block overlaps the kernel text mapping.
+	 * This block overlaps the kernel text/rodata mapping.
 	 * Map the portion(s) which don't overlap.
 	 */
 	if (start < kernel_start)
@@ -417,7 +417,7 @@ static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end
 				     early_pgtable_alloc);
 
 	/*
-	 * Map the linear alias of the [_stext, _etext) interval as
+	 * Map the linear alias of the [_stext, __init_begin) interval as
 	 * read-only/non-executable. This makes the contents of the
 	 * region accessible to subsystems such as hibernate, but
 	 * protects it from inadvertent modification or execution.
@@ -447,12 +447,18 @@ 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)_etext - (unsigned long)_stext;
 	create_mapping_late(__pa(_stext), (unsigned long)_stext,
-				(unsigned long)__init_begin - (unsigned long)_stext,
-				PAGE_KERNEL_ROX);
+			    section_size, PAGE_KERNEL_ROX);
+	/*
+	 * mark .rodata as read only. Use __init_begin rather than __end_rodata
+	 * to cover NOTES and EXCEPTION_TABLE.
+	 */
+	section_size = (unsigned long)__init_begin - (unsigned long)__start_rodata;
+	create_mapping_late(__pa(__start_rodata), (unsigned long)__start_rodata,
+			    section_size, PAGE_KERNEL_RO);
 }
 
 void fixup_init(void)
@@ -491,9 +497,10 @@ 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, __start_rodata, __init_begin, 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);