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arm64: proton-pack: Report Spectre-BHB vulnerabilities as part of Spectre-v2
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> Signed-off-by: James Morse <james.morse@arm.com>
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2 changed files with 36 additions and 2 deletions
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@ -93,5 +93,7 @@ void spectre_v4_enable_task_mitigation(struct task_struct *tsk);
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enum mitigation_state arm64_get_meltdown_state(void);
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enum mitigation_state arm64_get_spectre_bhb_state(void);
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#endif /* __ASSEMBLY__ */
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#endif /* __ASM_SPECTRE_H */
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@ -96,14 +96,39 @@ static bool spectre_v2_mitigations_off(void)
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return ret;
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}
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static const char *get_bhb_affected_string(enum mitigation_state bhb_state)
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{
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switch (bhb_state) {
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case SPECTRE_UNAFFECTED:
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return "";
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default:
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case SPECTRE_VULNERABLE:
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return ", but not BHB";
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case SPECTRE_MITIGATED:
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return ", BHB";
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}
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}
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ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
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char *buf)
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{
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enum mitigation_state bhb_state = arm64_get_spectre_bhb_state();
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const char *bhb_str = get_bhb_affected_string(bhb_state);
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const char *v2_str = "Branch predictor hardening";
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switch (spectre_v2_state) {
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case SPECTRE_UNAFFECTED:
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return sprintf(buf, "Not affected\n");
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if (bhb_state == SPECTRE_UNAFFECTED)
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return sprintf(buf, "Not affected\n");
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/*
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* Platforms affected by Spectre-BHB can't report
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* "Not affected" for Spectre-v2.
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*/
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v2_str = "CSV2";
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fallthrough;
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case SPECTRE_MITIGATED:
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return sprintf(buf, "Mitigation: Branch predictor hardening\n");
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return sprintf(buf, "Mitigation: %s%s\n", v2_str, bhb_str);
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case SPECTRE_VULNERABLE:
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fallthrough;
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default:
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@ -771,6 +796,13 @@ int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
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}
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}
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static enum mitigation_state spectre_bhb_state;
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enum mitigation_state arm64_get_spectre_bhb_state(void)
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{
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return spectre_bhb_state;
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}
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/* Patched to NOP when enabled */
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void noinstr spectre_bhb_patch_loop_mitigation_enable(struct alt_instr *alt,
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__le32 *origptr,
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