arm64: avoid overflow in VA_START and PAGE_OFFSET
authorNick Desaulniers <ndesaulniers@google.com>
Thu, 3 Aug 2017 18:03:58 +0000 (11:03 -0700)
committerWill Deacon <will.deacon@arm.com>
Fri, 4 Aug 2017 14:06:35 +0000 (15:06 +0100)
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@linaro.org>
Suggested-by: Yury Norov <ynorov@caviumnetworks.com>
Suggested-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
arch/arm64/include/asm/memory.h

index 32f82723338a0e23bd880273aa9ae53e93a9979d..ef39dcb9ca6af1150152883cf338114536167b5f 100644 (file)
  * TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area.
  */
 #define VA_BITS                        (CONFIG_ARM64_VA_BITS)
  * TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area.
  */
 #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 KIMAGE_VADDR           (MODULES_END)
 #define MODULES_END            (MODULES_VADDR + MODULES_VSIZE)
 #define MODULES_VADDR          (VA_START + KASAN_SHADOW_SIZE)
 #define KIMAGE_VADDR           (MODULES_END)
 #define MODULES_END            (MODULES_VADDR + MODULES_VSIZE)
 #define MODULES_VADDR          (VA_START + KASAN_SHADOW_SIZE)