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 | 8 ++++++ arch/arm64/kernel/cpu_errata.c | 38 ++++++++++++++++++++++++++--- 2 files changed, 43 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index dda6e5056810..e59b9ee43e4a 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -527,6 +527,14 @@ 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); #endif /* __ASSEMBLY__ */
#endif diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c index d191ce8410db..d055ed21eeeb 100644 --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -875,14 +875,39 @@ 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) { - if (__spectrev2_safe) - return sprintf(buf, "Not affected\n"); + 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"; + + if (__spectrev2_safe) { + 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"; + }
if (__hardenbp_enab) - return sprintf(buf, "Mitigation: Branch predictor hardening\n"); + return sprintf(buf, "Mitigation: %s%s\n", v2_str, bhb_str);
return sprintf(buf, "Vulnerable\n"); } @@ -903,3 +928,10 @@ 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; +}