[PATCH] arm64: cputype: Avoid overflow using MIDR_IMPLEMENTOR_MASK

[PATCH] arm64: cputype: Avoid overflow using MIDR_IMPLEMENTOR_MASK

[Michal Orzel]

Value of macro MIDR_IMPLEMENTOR_MASK exceeds the range of integer
and can lead to overflow. Currently there is no issue as it is used
in expressions implicitly casting it to u32. To avoid possible
problems, fix the macro.

Signed-off-by: Michal Orzel <michal.orzel@arm.com>
---
Should we also add a U suffix to ARM_CPU_IMP_* macros that are also shifted
by MIDR_IMPLEMENTOR_SHIFT? None of them has bit 7 set but we could take some
precaution steps.
---
 arch/arm64/include/asm/cputype.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/cputype.h b/arch/arm64/include/asm/cputype.h
index ff8f4511df71..92331c07c2d1 100644
--- a/arch/arm64/include/asm/cputype.h
+++ b/arch/arm64/include/asm/cputype.h
@@ -36,7 +36,7 @@
 #define MIDR_VARIANT(midr)	\
 	(((midr) & MIDR_VARIANT_MASK) >> MIDR_VARIANT_SHIFT)
 #define MIDR_IMPLEMENTOR_SHIFT	24
-#define MIDR_IMPLEMENTOR_MASK	(0xff << MIDR_IMPLEMENTOR_SHIFT)
+#define MIDR_IMPLEMENTOR_MASK	(0xffU << MIDR_IMPLEMENTOR_SHIFT)
 #define MIDR_IMPLEMENTOR(midr)	\
 	(((midr) & MIDR_IMPLEMENTOR_MASK) >> MIDR_IMPLEMENTOR_SHIFT)
 
-- 
2.25.1


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Re: [PATCH] arm64: cputype: Avoid overflow using MIDR_IMPLEMENTOR_MASK

[Catalin Marinas]

On Tue, Apr 26, 2022 at 09:06:03AM +0200, Michal Orzel wrote:
> Value of macro MIDR_IMPLEMENTOR_MASK exceeds the range of integer
> and can lead to overflow. Currently there is no issue as it is used
> in expressions implicitly casting it to u32. To avoid possible
> problems, fix the macro.
> 
> Signed-off-by: Michal Orzel <michal.orzel@arm.com>
> ---
> Should we also add a U suffix to ARM_CPU_IMP_* macros that are also shifted
> by MIDR_IMPLEMENTOR_SHIFT? None of them has bit 7 set but we could take some
> precaution steps.

I'm ok with not adding it now. We haven't been consistent with this but
we did encounter a few issues in the past with other bits and only fixed
those that were touching bit 31.

-- 
Catalin

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Re: [PATCH] arm64: cputype: Avoid overflow using MIDR_IMPLEMENTOR_MASK

[Catalin Marinas]

On Tue, 26 Apr 2022 09:06:03 +0200, Michal Orzel wrote:
> Value of macro MIDR_IMPLEMENTOR_MASK exceeds the range of integer
> and can lead to overflow. Currently there is no issue as it is used
> in expressions implicitly casting it to u32. To avoid possible
> problems, fix the macro.
> 
> 

Applied to arm64 (for-next/misc), thanks!

[1/1] arm64: cputype: Avoid overflow using MIDR_IMPLEMENTOR_MASK
      https://git.kernel.org/arm64/c/48e6f22e25a4

-- 
Catalin


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