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arm64: add sysfs vulnerability show for meltdown 

We implement page table isolation as a mitigation for meltdown.
Report this to userspace via sysfs.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Jeremy Linton 2019-04-15 16:21:22 -05:00 committed by Will Deacon
parent 3891ebccac
commit 1b3ccf4be0
1 changed files with 44 additions and 14 deletions
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58
arch/arm64/kernel/cpufeature.c
View File

@ -947,7 +947,7 @@ 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,
@ -967,6 +967,16 @@ 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
@ -978,6 +988,19 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
__kpti_forced = -1;
}
/* Useful for KASLR robustness */
if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && kaslr_offset() > 0) {
if (!__kpti_forced) {
str = "KASLR";
__kpti_forced = 1;
}
}
if (!IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0)) {
pr_info_once("kernel page table isolation disabled by kernel configuration\n");
return false;
}
/* Forced? */
if (__kpti_forced) {
pr_info_once("kernel page table isolation forced %s by %s\n",
@ -985,18 +1008,10 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
return __kpti_forced > 0;
}
/* Useful for KASLR robustness */
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)
{
@ -1026,6 +1041,12 @@ 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)
{
@ -1039,7 +1060,6 @@ 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)
@ -1306,7 +1326,6 @@ 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,
@ -1322,7 +1341,6 @@ 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,
@ -2101,3 +2119,15 @@ 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 (__meltdown_safe)
return sprintf(buf, "Not affected\n");
if (arm64_kernel_unmapped_at_el0())
return sprintf(buf, "Mitigation: PTI\n");
return sprintf(buf, "Vulnerable\n");
}