Messages in this thread | | | Subject | Re: [PATCH v5 03/10] arm64: add sysfs vulnerability show for meltdown | From | Andre Przywara <> | Date | Fri, 1 Mar 2019 01:11:05 -0600 |
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Hi,
On 2/26/19 7:05 PM, Jeremy Linton wrote: > Display the mitigation status if active, otherwise > assume the cpu is safe unless it doesn't have CSV3 > and isn't in our whitelist. > > Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> > --- > arch/arm64/kernel/cpufeature.c | 47 ++++++++++++++++++++++++++-------- > 1 file changed, 37 insertions(+), 10 deletions(-) > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index f6d84e2c92fe..d31bd770acba 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -944,7 +944,7 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope) > return has_cpuid_feature(entry, scope); > } > > -#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > +static bool __meltdown_safe = true; > 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, > @@ -963,6 +963,16 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, > { /* sentinel */ } > }; > char const *str = "command line option"; > + bool meltdown_safe; > + > + meltdown_safe = is_midr_in_range_list(read_cpuid_id(), kpti_safe_list); > + > + /* Defer to CPU feature registers */ > + if (has_cpuid_feature(entry, scope)) > + meltdown_safe = true; > + > + if (!meltdown_safe) > + __meltdown_safe = false; > > /* > * For reasons that aren't entirely clear, enabling KPTI on Cavium > @@ -974,6 +984,11 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, > __kpti_forced = -1; > } > > + if (!IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0)) { > + pr_info_once("kernel page table isolation disabled by CONFIG\n"); > + return false; > + } > + > /* Forced? */ > if (__kpti_forced) { > pr_info_once("kernel page table isolation forced %s by %s\n", > @@ -985,14 +1000,10 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry, > if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) > return kaslr_offset() > 0; > > - /* Don't force KPTI for CPUs that are not vulnerable */ > - if (is_midr_in_range_list(read_cpuid_id(), kpti_safe_list)) > - return false; > - > - /* Defer to CPU feature registers */ > - return !has_cpuid_feature(entry, scope); > + return !meltdown_safe; > } > > +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > static void > kpti_install_ng_mappings(const struct arm64_cpu_capabilities *__unused) > { > @@ -1022,6 +1033,13 @@ kpti_install_ng_mappings(const struct arm64_cpu_capabilities *__unused) > > return; > } > +#else > +static void > +kpti_install_ng_mappings(const struct arm64_cpu_capabilities *__unused) > +{ > +} > +#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */ > + > > static int __init parse_kpti(char *str) > { > @@ -1035,7 +1053,6 @@ static int __init parse_kpti(char *str) > return 0; > } > early_param("kpti", parse_kpti); > -#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */ > > #ifdef CONFIG_ARM64_HW_AFDBM > static inline void __cpu_enable_hw_dbm(void) > @@ -1286,7 +1303,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = { > .field_pos = ID_AA64PFR0_EL0_SHIFT, > .min_field_value = ID_AA64PFR0_EL0_32BIT_64BIT, > }, > -#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > { > .desc = "Kernel page table isolation (KPTI)", > .capability = ARM64_UNMAP_KERNEL_AT_EL0, > @@ -1302,7 +1318,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = { > .matches = unmap_kernel_at_el0, > .cpu_enable = kpti_install_ng_mappings, > }, > -#endif > { > /* FP/SIMD is not implemented */ > .capability = ARM64_HAS_NO_FPSIMD, > @@ -2063,3 +2078,15 @@ static int __init enable_mrs_emulation(void) > } > > core_initcall(enable_mrs_emulation); > + > +ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, > + char *buf) > +{ > + if (arm64_kernel_unmapped_at_el0()) > + return sprintf(buf, "Mitigation: KPTI\n"); > + > + if (__meltdown_safe) > + return sprintf(buf, "Not affected\n");
Shall those two checks be swapped? So it doesn't report about a KPTI mitigation if the CPU is safe, but we enable KPTI because of KASLR having enabled it? Or is that a different knob?
Cheers, Andre.
> + > + return sprintf(buf, "Vulnerable\n"); > +} >
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