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>

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 4061de1..703ee85 100644 (file)
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -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");
+}