Messages in this thread | | | Subject | Re: [PATCH v5 03/10] arm64: add sysfs vulnerability show for meltdown | From | Jeremy Linton <> | Date | Fri, 1 Mar 2019 10:53:50 -0600 |
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Hi,
On 3/1/19 10:20 AM, Catalin Marinas wrote: > On Fri, Mar 01, 2019 at 10:12:09AM -0600, Jeremy Linton wrote: >> On 3/1/19 1:11 AM, Andre Przywara wrote: >>> 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? >> >> Hmmm, I think having it this way reflects the fact that the machine is >> mitigated independent of whether it needed it. The force on case is similar. >> The machine may not have needed the mitigation but it was forced on. > > So is this patchset about showing vulnerabilities _and_ mitigations or > just one of them? >
Well, I don't think there is a way to express a mitigated but not vulnerable state in the current ABI. This set is mostly just to bring us in line with the current ABI expectations.
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