Patchwork arm64: avoid overflow in VA_START and PAGE_OFFSET

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Submitter Nick Desaulniers
Date Aug. 3, 2017, 5:11 p.m.
Message ID <20170803171117.107992-1-ndesaulniers@google.com>
Download mbox | patch
Permalink /patch/9879533/
State New
Headers show

Comments

Nick Desaulniers - Aug. 3, 2017, 5:11 p.m.
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@caviumnetworks.com>
Suggested-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 arch/arm64/include/asm/memory.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
Ard Biesheuvel - Aug. 3, 2017, 5:20 p.m.
On 3 August 2017 at 18:11, Nick Desaulniers <ndesaulniers@google.com> wrote:
> 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@caviumnetworks.com>
> Suggested-by: Matthias Kaehlcke <mka@chromium.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.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
>

Would

#define VA_START (UL(0xffffffffffffffff) - (1 << VA_BITS) + 1)

also work?
Nick Desaulniers - Aug. 3, 2017, 5:53 p.m.
> Would
>
> #define VA_START (UL(0xffffffffffffffff) - (1 << VA_BITS) + 1)
>
> also work?

I think you'd have to wrap the 1 in a UL(), ex:

#define VA_START (UL(0xffffffffffffffff) - (UL(1) << VA_BITS) + 1)

Otherwise IIUC a integral literal (`1`) is treated as an int, which on
arm64 is LP64 making it 32b, where most configs set VA_BITS
to larger than 32b.  Shifting by more than the width is undefined
behavior. And without it, I get compile errors.

I'll send v2 with your suggestion, thanks.

Patch

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)