From: James Morse james.morse@arm.com
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 Signed-off-by: James Morse james.morse@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/include/asm/spectre.h | 2 ++ arch/arm64/kernel/proton-pack.c | 36 ++++++++++++++++++++++++++++++++++-- 2 files changed, 36 insertions(+), 2 deletions(-)
--- a/arch/arm64/include/asm/spectre.h +++ b/arch/arm64/include/asm/spectre.h @@ -29,4 +29,6 @@ bool has_spectre_v4(const struct arm64_c void spectre_v4_enable_mitigation(const struct arm64_cpu_capabilities *__unused); void spectre_v4_enable_task_mitigation(struct task_struct *tsk);
+enum mitigation_state arm64_get_spectre_bhb_state(void); + #endif /* __ASM_SPECTRE_H */ --- a/arch/arm64/kernel/proton-pack.c +++ b/arch/arm64/kernel/proton-pack.c @@ -94,14 +94,39 @@ static bool spectre_v2_mitigations_off(v return ret; }
+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 (spectre_v2_state) { case SPECTRE_UNAFFECTED: - return sprintf(buf, "Not affected\n"); + 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 SPECTRE_MITIGATED: - return sprintf(buf, "Mitigation: Branch predictor hardening\n"); + return sprintf(buf, "Mitigation: %s%s\n", v2_str, bhb_str); case SPECTRE_VULNERABLE: fallthrough; default: @@ -787,3 +812,10 @@ int arch_prctl_spec_ctrl_get(struct task return -ENODEV; } } + +static enum mitigation_state spectre_bhb_state; + +enum mitigation_state arm64_get_spectre_bhb_state(void) +{ + return spectre_bhb_state; +}