[stable:PATCH v5.4.184 18/22] arm64: proton-pack: Report Spectre-BHB vulnerabilities as part of Spectre-v2

James Morse
2022-03-15T18:32:59Z

commit dee435be76f4117410bbd90573a881fd33488f37 upstream.

Speculation attacks against some high-performance processors can
make use of branch history to influence future speculation as part of
a spectre-v2 attack. This is not mitigated by CSV2, meaning CPUs that
previously reported 'Not affected' are now moderately mitigated by CSV2.

Update the value in /sys/devices/system/cpu/vulnerabilities/spectre_v2
to also show the state of the BHB mitigation.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
[ code move to cpu_errata.c for backport ]
Signed-off-by: James Morse <james.morse@arm.com>
---
arch/arm64/include/asm/cpufeature.h | 9 +++++++
arch/arm64/kernel/cpu_errata.c | 41 ++++++++++++++++++++++++++---
2 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index ccae05da98a7..a798443ed76f 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -639,6 +639,15 @@ static inline int arm64_get_ssbd_state(void)

void arm64_set_ssbd_mitigation(bool state);

+/* Watch out, ordering is important here. */
+enum mitigation_state {
+ SPECTRE_UNAFFECTED,
+ SPECTRE_MITIGATED,
+ SPECTRE_VULNERABLE,
+};
+
+enum mitigation_state arm64_get_spectre_bhb_state(void);
+
extern int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);

static inline u32 id_aa64mmfr0_parange_to_phys_shift(int parange)
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 1e16c4e00e77..182305000de3 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -989,15 +989,41 @@ ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr,
return sprintf(buf, "Mitigation: __user pointer sanitization\n");
}

+static const char *get_bhb_affected_string(enum mitigation_state bhb_state)
+{
+ switch (bhb_state) {
+ case SPECTRE_UNAFFECTED:
+ return "";
+ default:
+ case SPECTRE_VULNERABLE:
+ return ", but not BHB";
+ case SPECTRE_MITIGATED:
+ return ", BHB";
+ }
+}
+
ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
char *buf)
{
+ enum mitigation_state bhb_state = arm64_get_spectre_bhb_state();
+ const char *bhb_str = get_bhb_affected_string(bhb_state);
+ const char *v2_str = "Branch predictor hardening";
+
switch (get_spectre_v2_workaround_state()) {
case ARM64_BP_HARDEN_NOT_REQUIRED:
- return sprintf(buf, "Not affected\n");
- case ARM64_BP_HARDEN_WA_NEEDED:
- return sprintf(buf, "Mitigation: Branch predictor hardening\n");
- case ARM64_BP_HARDEN_UNKNOWN:
+ if (bhb_state == SPECTRE_UNAFFECTED)
+ return sprintf(buf, "Not affected\n");
+
+ /*
+ * Platforms affected by Spectre-BHB can't report
+ * "Not affected" for Spectre-v2.
+ */
+ v2_str = "CSV2";
+ fallthrough;
+ case ARM64_BP_HARDEN_WA_NEEDED:
+ return sprintf(buf, "Mitigation: %s%s\n", v2_str, bhb_str);
+ case ARM64_BP_HARDEN_UNKNOWN:
+ fallthrough;
default:
return sprintf(buf, "Vulnerable\n");
}
@@ -1019,3 +1045,10 @@ ssize_t cpu_show_spec_store_bypass(struct device *dev,

return sprintf(buf, "Vulnerable\n");
}
+
+static enum mitigation_state spectre_bhb_state;
+
+enum mitigation_state arm64_get_spectre_bhb_state(void)
+{
+ return spectre_bhb_state;
+}