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arm64: Fix bit-shifting UB in the MIDR_CPU_MODEL() macro

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CONFIG_UBSAN_SHIFT with gcc-5 complains that the shifting of
ARM_CPU_IMP_AMPERE (0xC0) into bits [31:24] by MIDR_CPU_MODEL() is
undefined behavior. Well, sort of, it actually spells the error as:

 arch/arm64/kernel/proton-pack.c: In function 'spectre_bhb_loop_affected':
 arch/arm64/include/asm/cputype.h:44:2: error: initializer element is not constant
   (((imp)   << MIDR_IMPLEMENTOR_SHIFT) | \
   ^

This isn't an issue for other Implementor codes, as all the other codes
have zero in the top bit and so are representable as a signed int.

Cast the implementor code to unsigned in MIDR_CPU_MODEL to remove the
undefined behavior.

Fixes: 0e5d5ae837 ("arm64: Add AMPERE1 to the Spectre-BHB affected list")
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: D Scott Phillips <scott@os.amperecomputing.com>
Link: https://lore.kernel.org/r/20221102160106.1096948-1-scott@os.amperecomputing.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
D Scott Phillips 2022-11-02 09:01:06 -07:00 committed by Catalin Marinas
parent 2081b3bd0c
commit 8ec8490a19
1 changed files with 1 additions and 1 deletions
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2
arch/arm64/include/asm/cputype.h
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@ -41,7 +41,7 @@
(((midr) & MIDR_IMPLEMENTOR_MASK) >> MIDR_IMPLEMENTOR_SHIFT)
#define MIDR_CPU_MODEL(imp, partnum) \
(((imp) << MIDR_IMPLEMENTOR_SHIFT) | \
((_AT(u32, imp) << MIDR_IMPLEMENTOR_SHIFT) | \
(0xf << MIDR_ARCHITECTURE_SHIFT) | \
((partnum) << MIDR_PARTNUM_SHIFT))