From: Suzuki K Poulose suzuki.poulose@arm.com
[ Upstream commit d3aec8a28be3b88bf75442e7c24fd9da8d69a6df ]
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 Signed-off-by: Ard Biesheuvel ard.biesheuvel@linaro.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/include/asm/cpufeature.h | 9 +++++++++ arch/arm64/kernel/cpufeature.c | 16 +++++++++++----- 2 files changed, 20 insertions(+), 5 deletions(-)
--- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -244,6 +244,15 @@ extern struct arm64_ftr_reg arm64_ftr_re 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; --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -824,10 +824,9 @@ static bool has_no_fpsimd(const struct a 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 @@ -863,8 +862,7 @@ static bool unmap_kernel_at_el0(const st }
/* Defer to CPU feature registers */ - return !cpuid_feature_extract_unsigned_field(pfr0, - ID_AA64PFR0_CSV3_SHIFT); + return !has_cpuid_feature(entry, scope); }
static void @@ -1011,7 +1009,15 @@ static const struct arm64_cpu_capabiliti { .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, },