linux-kernel - [PATCH] arm64: avoid overflow in VA_START and PAGE

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Date:   Thu,  3 Aug 2017 10:11:16 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     zijun_hu@....com, akpm@...ux-foundation.org, ghackmann@...gle.com,
        dianders@...omium.org, srhines@...gle.com, pirama@...gle.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Laura Abbott <labbott@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Oleksandr Andrushchenko <Oleksandr_Andrushchenko@...m.com>,
        Alexander Popov <alex.popov@...ux.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] arm64: avoid overflow in VA_START and PAGE_OFFSET

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: Yury Norov <ynorov@...iumnetworks.com>
Suggested-by: Matthias Kaehlcke <mka@...omium.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 arch/arm64/include/asm/memory.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 32f82723338a..dde717a31dee 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -64,8 +64,9 @@
  * 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) >> VA_BITS) << VA_BITS)
+#define PAGE_OFFSET		((UL(0xffffffffffffffff) >> (VA_BITS - 1)) \
+	<< (VA_BITS - 1))
 #define KIMAGE_VADDR		(MODULES_END)
 #define MODULES_END		(MODULES_VADDR + MODULES_VSIZE)
 #define MODULES_VADDR		(VA_START + KASAN_SHADOW_SIZE)
-- 
2.14.0.rc1.383.gd1ce394fe2-goog