@@ -944,6 +944,9 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope)
return has_cpuid_feature(entry, scope);
}
+/* default value is invalid until unmap_kernel_at_el0() runs */
+static bool __meltdown_safe = true;
+
#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */
@@ -972,6 +975,12 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
{
char const *str = "command line option";
+ bool meltdown_safe = is_cpu_meltdown_safe() ||
+ has_cpuid_feature(entry, scope);
+
+ if (!meltdown_safe)
+ __meltdown_safe = false;
+
/*
* For reasons that aren't entirely clear, enabling KPTI on Cavium
* ThunderX leads to apparent I-cache corruption of kernel text, which
@@ -993,11 +1002,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
return true;
- if (is_cpu_meltdown_safe())
- return false;
-
- /* Defer to CPU feature registers */
- return !has_cpuid_feature(entry, scope);
+ return !meltdown_safe;
}
static void
@@ -2065,3 +2070,17 @@ static int __init enable_mrs_emulation(void)
}
core_initcall(enable_mrs_emulation);
+
+#ifdef CONFIG_GENERIC_CPU_VULNERABILITIES
+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 (IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0) && __meltdown_safe)
+ return sprintf(buf, "Not affected\n");
+
+ return sprintf(buf, "Unknown\n");
+}
+#endif
Add a simple state machine which will track whether all the online cores in a machine are vulnerable. Once that is done we have a fairly authoritative view of the machine vulnerability, which allows us to make a judgment about machine safety if it hasn't been mitigated. Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> --- arch/arm64/kernel/cpufeature.c | 29 ++++++++++++++++++++++++----- 1 file changed, 24 insertions(+), 5 deletions(-)