[PATCH 4.4 28/72] arm64: avoid overflow in VA_START and PAGE_OFFSET

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

commit 82cd588052815eb4146f9f7c5347ca5e32c56360 upstream.

The bitmask used to define these values produces overflow, as seen by
this compiler warning:

arch/arm64/kernel/head.S:47:8: warning:
      integer overflow in preprocessor expression
  #elif (PAGE_OFFSET & 0x1fffff) != 0
         ^~~~~~~~~~~
arch/arm64/include/asm/memory.h:52:46: note:
      expanded from macro 'PAGE_OFFSET'
  #define PAGE_OFFSET             (UL(0xffffffffffffffff) << (VA_BITS -
1))
                                      ~~~~~~~~~~~~~~~~~~  ^

It would be preferrable to use GENMASK_ULL() instead, but it's not set
up to be used from assembly (the UL() macro token pastes UL suffixes
when not included in assembly sources).

Suggested-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Suggested-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
Suggested-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
[natechancellor: KIMAGE_VADDR doesn't exist]
Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/include/asm/memory.h |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -49,8 +49,10 @@
  * and PAGE_OFFSET - it must be within 128MB of the kernel text.
  */
 #define VA_BITS			(CONFIG_ARM64_VA_BITS)
-#define VA_START		(UL(0xffffffffffffffff) << VA_BITS)
-#define PAGE_OFFSET		(UL(0xffffffffffffffff) << (VA_BITS - 1))
+#define VA_START		(UL(0xffffffffffffffff) - \
+	(UL(1) << VA_BITS) + 1)
+#define PAGE_OFFSET		(UL(0xffffffffffffffff) - \
+	(UL(1) << (VA_BITS - 1)) + 1)
 #define MODULES_END		(PAGE_OFFSET)
 #define MODULES_VADDR		(MODULES_END - SZ_64M)
 #define PCI_IO_END		(MODULES_VADDR - SZ_2M)