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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 <[email protected]>
Signed-off-by: D Scott Phillips <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>
This commit is contained in:
D Scott Phillips authored and Catalin Marinas committed 2022-11-09 09:51:39 +00:00
1 parent 2081b3bd0c
commit 8ec8490a19
1 file changed
+1 -1
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arch/arm64/include/asm/cputype.h
+1 -1
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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))