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| author | Suzuki K Poulose <suzuki.poulose@arm.com> | 2018-03-26 15:12:40 +0100 |
|---|---|---|
| committer | Will Deacon <will.deacon@arm.com> | 2018-03-26 18:01:40 +0100 |
| commit | d3aec8a28be3b88bf75442e7c24fd9da8d69a6df (patch) | |
| tree | 14768c5c5b61bf2d7d78140c46a30580547323ad /arch/arm64 | |
| parent | 5c137714dd8cae464dbd5f028c07af149e6d09fc (diff) | |
| download | blackbird-op-linux-d3aec8a28be3b88bf75442e7c24fd9da8d69a6df.tar.gz blackbird-op-linux-d3aec8a28be3b88bf75442e7c24fd9da8d69a6df.zip | |
arm64: capabilities: Restrict KPTI detection to boot-time CPUs
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>
Diffstat (limited to 'arch/arm64')
| -rw-r--r-- | arch/arm64/include/asm/cpufeature.h | 9 | ||||
| -rw-r--r-- | arch/arm64/kernel/cpufeature.c | 16 |
2 files changed, 20 insertions, 5 deletions
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index effb1c038221..4f050259dff3 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -248,6 +248,15 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0; ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU | \ ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU) +/* + * CPU feature detected at boot time, on one or more CPUs. A late CPU + * is not allowed to have the capability when the system doesn't have it. + * It is Ok for a late CPU to miss the feature. + */ +#define ARM64_CPUCAP_BOOT_RESTRICTED_CPU_LOCAL_FEATURE \ + (ARM64_CPUCAP_SCOPE_LOCAL_CPU | \ + ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU) + struct arm64_cpu_capabilities { const char *desc; u16 capability; diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index a80ca94080b7..cae3dcef0efa 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -880,10 +880,9 @@ static bool has_cache_dic(const struct arm64_cpu_capabilities *entry, static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, - int __unused) + int scope) { char const *str = "command line option"; - u64 pfr0 = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1); /* * For reasons that aren't entirely clear, enabling KPTI on Cavium @@ -914,8 +913,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, } /* Defer to CPU feature registers */ - return !cpuid_feature_extract_unsigned_field(pfr0, - ID_AA64PFR0_CSV3_SHIFT); + return !has_cpuid_feature(entry, scope); } static void @@ -1062,7 +1060,15 @@ static const struct arm64_cpu_capabilities arm64_features[] = { { .desc = "Kernel page table isolation (KPTI)", .capability = ARM64_UNMAP_KERNEL_AT_EL0, - .type = ARM64_CPUCAP_SYSTEM_FEATURE, + .type = ARM64_CPUCAP_BOOT_RESTRICTED_CPU_LOCAL_FEATURE, + /* + * The ID feature fields below are used to indicate that + * the CPU doesn't need KPTI. See unmap_kernel_at_el0 for + * more details. + */ + .sys_reg = SYS_ID_AA64PFR0_EL1, + .field_pos = ID_AA64PFR0_CSV3_SHIFT, + .min_field_value = 1, .matches = unmap_kernel_at_el0, .cpu_enable = kpti_install_ng_mappings, }, |
