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Subject[PATCH 4.19 100/114] arm64: add sysfs vulnerability show for spectre-v2
Date
From: Jeremy Linton <jeremy.linton@arm.com>

[ Upstream commit d2532e27b5638bb2e2dd52b80b7ea2ec65135377 ]

Track whether all the cores in the machine are vulnerable to Spectre-v2,
and whether all the vulnerable cores have been mitigated. We then expose
this information to userspace via sysfs.

Signed-off-by: Jeremy Linton <jeremy.linton@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>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm64/kernel/cpu_errata.c | 27 ++++++++++++++++++++++++++-
1 file changed, 26 insertions(+), 1 deletion(-)

--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -480,6 +480,10 @@ has_cortex_a76_erratum_1463225(const str
.type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM, \
CAP_MIDR_RANGE_LIST(midr_list)

+/* Track overall mitigation state. We are only mitigated if all cores are ok */
+static bool __hardenbp_enab = true;
+static bool __spectrev2_safe = true;
+
/*
* Generic helper for handling capabilties with multiple (match,enable) pairs
* of call backs, sharing the same capability bit.
@@ -522,6 +526,10 @@ static const struct midr_range spectre_v
{ /* sentinel */ }
};

+/*
+ * Track overall bp hardening for all heterogeneous cores in the machine.
+ * We are only considered "safe" if all booted cores are known safe.
+ */
static bool __maybe_unused
check_branch_predictor(const struct arm64_cpu_capabilities *entry, int scope)
{
@@ -543,6 +551,8 @@ check_branch_predictor(const struct arm6
if (!need_wa)
return false;

+ __spectrev2_safe = false;
+
if (!IS_ENABLED(CONFIG_HARDEN_BRANCH_PREDICTOR)) {
pr_warn_once("spectrev2 mitigation disabled by kernel configuration\n");
__hardenbp_enab = false;
@@ -552,11 +562,14 @@ check_branch_predictor(const struct arm6
/* forced off */
if (__nospectre_v2) {
pr_info_once("spectrev2 mitigation disabled by command line option\n");
+ __hardenbp_enab = false;
return false;
}

- if (need_wa < 0)
+ if (need_wa < 0) {
pr_warn_once("ARM_SMCCC_ARCH_WORKAROUND_1 missing from firmware\n");
+ __hardenbp_enab = false;
+ }

return (need_wa > 0);
}
@@ -753,3 +766,15 @@ ssize_t cpu_show_spectre_v1(struct devic
{
return sprintf(buf, "Mitigation: __user pointer sanitization\n");
}
+
+ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ if (__spectrev2_safe)
+ return sprintf(buf, "Not affected\n");
+
+ if (__hardenbp_enab)
+ return sprintf(buf, "Mitigation: Branch predictor hardening\n");
+
+ return sprintf(buf, "Vulnerable\n");
+}

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