arm64: capabilities: Restrict KPTI detection to boot-time CPUs

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KPTI is treated as a system wide feature and is only detected if all
the CPUs in the sysetm needs the defense, unless it is forced via kernel
command line. This leaves a system with a mix of CPUs with and without
the defense vulnerable. Also, if a late CPU needs KPTI but KPTI was not
activated at boot time, the CPU is currently allowed to boot, which is a
potential security vulnerability.
This patch ensures that the KPTI is turned on if at least one CPU detects
the capability (i.e, change scope to SCOPE_LOCAL_CPU). Also rejetcs a late
CPU, if it requires the defense, when the system hasn't enabled it,

Cc: Will Deacon <will.deacon@arm.com>
Reviewed-by: Dave Martin <dave.martin@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

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Suzuki K Poulose 2018-03-26 15:12:40 +01:00 • committed by Will Deacon

parent 5c137714dd

commit d3aec8a28b

2 changed files with 20 additions and 5 deletions

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9

arch/arm64/include/asm/cpufeature.h

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16

arch/arm64/kernel/cpufeature.c

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