Patch "arm64: mm: use correct mapping granularity under DEBUG_RODATA" has been added to the 4.3-stable tree

This is a note to let you know that I've just added the patch titled

arm64: mm: use correct mapping granularity under DEBUG_RODATA

to the 4.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm64-mm-use-correct-mapping-granularity-under-debug_rodata.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ard Biesheuvel <[email protected]>
Date: Mon, 16 Nov 2015 11:18:14 +0100
Subject: arm64: mm: use correct mapping granularity under DEBUG_RODATA

From: Ard Biesheuvel <[email protected]>

commit 4fee9f364b9b99f76732f2a6fd6df679a237fa74 upstream.

When booting a 64k pages kernel that is built with CONFIG_DEBUG_RODATA and resides at an offset that is not a multiple of 512 MB, the rounding that occurs in __map_memblock() and fixup_executable() results in incorrect regions being mapped.

The following snippet from /sys/kernel/debug/kernel_page_tables shows how, when the kernel is loaded 2 MB above the base of DRAM at 0x40000000, the first 2 MB of memory (which may be inaccessible from non-secure EL1 or just reserved by the firmware) is inadvertently mapped into the end of the module region.

---[ Modules start ]---
0xfffffdffffe00000-0xfffffe0000000000 2M RW NX ... UXN MEM/NORMAL
---[ Modules end ]---
---[ Kernel Mapping ]---
0xfffffe0000000000-0xfffffe0000090000 576K RW NX ... UXN MEM/NORMAL

  0xfffffe0000090000-0xfffffe0000200000  1472K ro x  ... UXN MEM/NORMAL
  0xfffffe0000200000-0xfffffe0000800000     6M ro x  ... UXN MEM/NORMAL
  0xfffffe0000800000-0xfffffe0000810000    64K ro x  ... UXN MEM/NORMAL

0xfffffe0000810000-0xfffffe0000a00000 1984K RW NX ... UXN MEM/NORMAL 0xfffffe0000a00000-0xfffffe00ffe00000 4084M RW NX ... UXN MEM/NORMAL

The same issue is likely to occur on 16k pages kernels whose load address is not a multiple of 32 MB (i.e., SECTION_SIZE). So round to SWAPPER_BLOCK_SIZE instead of SECTION_SIZE.

---
 arch/arm64/mm/mmu.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

@@ -301,6 +301,7 @@ static void create_mapping_late(phys_add
 }
 
 #ifdef CONFIG_DEBUG_RODATA
+#define SWAPPER_BLOCK_SIZE	(PAGE_SHIFT == 12 ? SECTION_SIZE : PAGE_SIZE)
 static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
 {
 	/*

@@ -308,8 +309,8 @@ static void __init __map_memblock(phys_a
 	 * for now. This will get more fine grained later once all memory
 	 * is mapped
 	 */
-	unsigned long kernel_x_start = round_down(__pa(_stext), SECTION_SIZE);
-	unsigned long kernel_x_end = round_up(__pa(__init_end), SECTION_SIZE);
+	unsigned long kernel_x_start = round_down(__pa(_stext), SWAPPER_BLOCK_SIZE);
+	unsigned long kernel_x_end = round_up(__pa(__init_end), SWAPPER_BLOCK_SIZE);
 
 	if (end < kernel_x_start) {
 		create_mapping(start, __phys_to_virt(start),

@@ -397,18 +398,18 @@ void __init fixup_executable(void)
 {
 #ifdef CONFIG_DEBUG_RODATA
 	/* now that we are actually fully mapped, make the start/end more fine grained */
-	if (!IS_ALIGNED((unsigned long)_stext, SECTION_SIZE)) {
+	if (!IS_ALIGNED((unsigned long)_stext, SWAPPER_BLOCK_SIZE)) {
 		unsigned long aligned_start = round_down(__pa(_stext),
-							SECTION_SIZE);
+							 SWAPPER_BLOCK_SIZE);
 
 		create_mapping(aligned_start, __phys_to_virt(aligned_start),
 				__pa(_stext) - aligned_start,
 				PAGE_KERNEL);
 	}
 
-	if (!IS_ALIGNED((unsigned long)__init_end, SECTION_SIZE)) {
+	if (!IS_ALIGNED((unsigned long)__init_end, SWAPPER_BLOCK_SIZE)) {
 		unsigned long aligned_end = round_up(__pa(__init_end),
-							SECTION_SIZE);
+							  SWAPPER_BLOCK_SIZE);
 		create_mapping(__pa(__init_end), (unsigned long)__init_end,
 				aligned_end - __pa(__init_end),
 				PAGE_KERNEL);

Patches currently in stable-queue which might be from [email protected] are

queue-4.3/arm64-mm-use-correct-mapping-granularity-under-debug_rodata.patch