| Message ID | 20190321230557.45107-10-jeremy.linton@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: add system vulnerability sysfs entries | expand |
Hi Jeremy, On Thu, Mar 21, 2019 at 06:05:56PM -0500, Jeremy Linton wrote: > Return status based on ssbd_state and the arm64 SSBS feature. If > the mitigation is disabled, or the firmware isn't responding then > return the expected machine state based on a new blacklist of known > vulnerable cores. > > Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> > Reviewed-by: Andre Przywara <andre.przywara@arm.com> > Tested-by: Stefan Wahren <stefan.wahren@i2se.com> > --- > arch/arm64/kernel/cpu_errata.c | 44 ++++++++++++++++++++++++++++++++++ > 1 file changed, 44 insertions(+) > > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c > index 6958dcdabf7d..172ffbabd597 100644 > --- a/arch/arm64/kernel/cpu_errata.c > +++ b/arch/arm64/kernel/cpu_errata.c > @@ -278,6 +278,7 @@ static int detect_harden_bp_fw(void) > DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required); > > int ssbd_state __read_mostly = ARM64_SSBD_KERNEL; > +static bool __ssb_safe = true; > > static const struct ssbd_options { > const char *str; > @@ -386,6 +387,9 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, > > WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible()); > > + if (is_midr_in_range_list(read_cpuid_id(), entry->midr_range_list)) > + __ssb_safe = false; > + Does this mean that we assume that CPUs not present in our table are not affected by speculative store bypass? I don't think that's a good assumption, because we don't necessary have knowledge about partner or future CPU implementations, so I think any CPU lists really have to be whitelists like they are for the other vulnerabilities. > if (this_cpu_has_cap(ARM64_SSBS)) { > required = false; > goto out_printmsg; > @@ -419,12 +423,14 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, > ssbd_state = ARM64_SSBD_UNKNOWN; > return false; > > + /* machines with mixed mitigation requirements must not return this */ > case SMCCC_RET_NOT_REQUIRED: > pr_info_once("%s mitigation not required\n", entry->desc); > ssbd_state = ARM64_SSBD_MITIGATED; > return false; > > case SMCCC_RET_SUCCESS: > + __ssb_safe = false; > required = true; > break; > > @@ -474,6 +480,16 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, > return required; > } > > +/* known vulnerable cores */ > +static const struct midr_range arm64_ssb_cpus[] = { > + MIDR_ALL_VERSIONS(MIDR_CORTEX_A57), > + MIDR_ALL_VERSIONS(MIDR_CORTEX_A72), > + MIDR_ALL_VERSIONS(MIDR_CORTEX_A73), > + MIDR_ALL_VERSIONS(MIDR_CORTEX_A75), > + MIDR_ALL_VERSIONS(MIDR_CORTEX_A76), > + {}, > +}; > + > static void __maybe_unused > cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused) > { > @@ -769,6 +785,7 @@ const struct arm64_cpu_capabilities arm64_errata[] = { > .capability = ARM64_SSBD, > .type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM, > .matches = has_ssbd_mitigation, > + .midr_range_list = arm64_ssb_cpus, > }, > #ifdef CONFIG_ARM64_ERRATUM_1188873 > { > @@ -807,3 +824,30 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, > > return sprintf(buf, "Vulnerable\n"); > } > + > +ssize_t cpu_show_spec_store_bypass(struct device *dev, > + struct device_attribute *attr, char *buf) > +{ > + /* > + * Two assumptions: First, ssbd_state reflects the worse case > + * for heterogeneous machines, and that if SSBS is supported its > + * supported by all cores. > + */ > + switch (ssbd_state) { > + case ARM64_SSBD_MITIGATED: > + return sprintf(buf, "Not affected\n"); > + > + case ARM64_SSBD_KERNEL: > + case ARM64_SSBD_FORCE_ENABLE: > + if (cpus_have_cap(ARM64_SSBS)) > + return sprintf(buf, "Not affected\n"); > + if (IS_ENABLED(CONFIG_ARM64_SSBD)) > + return sprintf(buf, > + "Mitigation: Speculative Store Bypass disabled\n"); x86 has a message about the prctl(), which we also support. Will
On Wed, 3 Apr 2019 17:50:05 +0100 Will Deacon <will.deacon@arm.com> wrote: > Hi Jeremy, > > On Thu, Mar 21, 2019 at 06:05:56PM -0500, Jeremy Linton wrote: > > Return status based on ssbd_state and the arm64 SSBS feature. If > > the mitigation is disabled, or the firmware isn't responding then > > return the expected machine state based on a new blacklist of known > > vulnerable cores. > > > > Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> > > Reviewed-by: Andre Przywara <andre.przywara@arm.com> > > Tested-by: Stefan Wahren <stefan.wahren@i2se.com> > > --- > > arch/arm64/kernel/cpu_errata.c | 44 ++++++++++++++++++++++++++++++++++ > > 1 file changed, 44 insertions(+) > > > > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c > > index 6958dcdabf7d..172ffbabd597 100644 > > --- a/arch/arm64/kernel/cpu_errata.c > > +++ b/arch/arm64/kernel/cpu_errata.c > > @@ -278,6 +278,7 @@ static int detect_harden_bp_fw(void) > > DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required); > > > > int ssbd_state __read_mostly = ARM64_SSBD_KERNEL; > > +static bool __ssb_safe = true; > > > > static const struct ssbd_options { > > const char *str; > > @@ -386,6 +387,9 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, > > > > WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible()); > > > > + if (is_midr_in_range_list(read_cpuid_id(), entry->midr_range_list)) > > + __ssb_safe = false; > > + > > Does this mean that we assume that CPUs not present in our table are not > affected by speculative store bypass? No, not affected are only those where we either have SSBS or the firmware explicitly returns SMCCC_RET_NOT_REQUIRED. This is governed by ssbd_state. So this doesn't affect correctness. __ssb_safe is an additional state just used for the sysfs output. But indeed it looks like this is wrong if the CPU is both not listed and the system doesn't provide the firmware interface: AFAICS we would report "Not affected" in this case. > I don't think that's a good > assumption, because we don't necessary have knowledge about partner or > future CPU implementations, so I think any CPU lists really have to be > whitelists like they are for the other vulnerabilities. I think the idea was to cover all those "legacy" systems which have older cores (no SSBS), but didn't get an firmware update. So your old Seattle would truthfully report "Vulnerable", but any random A53 device would report "Not affected", even with ancient firmware. Cheers, Andre. > > if (this_cpu_has_cap(ARM64_SSBS)) { > > required = false; > > goto out_printmsg; > > @@ -419,12 +423,14 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, > > ssbd_state = ARM64_SSBD_UNKNOWN; > > return false; > > > > + /* machines with mixed mitigation requirements must not return this */ > > case SMCCC_RET_NOT_REQUIRED: > > pr_info_once("%s mitigation not required\n", entry->desc); > > ssbd_state = ARM64_SSBD_MITIGATED; > > return false; > > > > case SMCCC_RET_SUCCESS: > > + __ssb_safe = false; > > required = true; > > break; > > > > @@ -474,6 +480,16 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, > > return required; > > } > > > > +/* known vulnerable cores */ > > +static const struct midr_range arm64_ssb_cpus[] = { > > + MIDR_ALL_VERSIONS(MIDR_CORTEX_A57), > > + MIDR_ALL_VERSIONS(MIDR_CORTEX_A72), > > + MIDR_ALL_VERSIONS(MIDR_CORTEX_A73), > > + MIDR_ALL_VERSIONS(MIDR_CORTEX_A75), > > + MIDR_ALL_VERSIONS(MIDR_CORTEX_A76), > > + {}, > > +}; > > + > > static void __maybe_unused > > cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused) > > { > > @@ -769,6 +785,7 @@ const struct arm64_cpu_capabilities arm64_errata[] = { > > .capability = ARM64_SSBD, > > .type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM, > > .matches = has_ssbd_mitigation, > > + .midr_range_list = arm64_ssb_cpus, > > }, > > #ifdef CONFIG_ARM64_ERRATUM_1188873 > > { > > @@ -807,3 +824,30 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, > > > > return sprintf(buf, "Vulnerable\n"); > > } > > + > > +ssize_t cpu_show_spec_store_bypass(struct device *dev, > > + struct device_attribute *attr, char *buf) > > +{ > > + /* > > + * Two assumptions: First, ssbd_state reflects the worse case > > + * for heterogeneous machines, and that if SSBS is supported its > > + * supported by all cores. > > + */ > > + switch (ssbd_state) { > > + case ARM64_SSBD_MITIGATED: > > + return sprintf(buf, "Not affected\n"); > > + > > + case ARM64_SSBD_KERNEL: > > + case ARM64_SSBD_FORCE_ENABLE: > > + if (cpus_have_cap(ARM64_SSBS)) > > + return sprintf(buf, "Not affected\n"); > > + if (IS_ENABLED(CONFIG_ARM64_SSBD)) > > + return sprintf(buf, > > + "Mitigation: Speculative Store Bypass disabled\n"); > > x86 has a message about the prctl(), which we also support. > > Will
On Fri, Apr 05, 2019 at 11:10:22AM +0100, Andre Przywara wrote: > On Wed, 3 Apr 2019 17:50:05 +0100 > Will Deacon <will.deacon@arm.com> wrote: > > > Hi Jeremy, > > > > On Thu, Mar 21, 2019 at 06:05:56PM -0500, Jeremy Linton wrote: > > > Return status based on ssbd_state and the arm64 SSBS feature. If > > > the mitigation is disabled, or the firmware isn't responding then > > > return the expected machine state based on a new blacklist of known > > > vulnerable cores. > > > > > > Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> > > > Reviewed-by: Andre Przywara <andre.przywara@arm.com> > > > Tested-by: Stefan Wahren <stefan.wahren@i2se.com> > > > --- > > > arch/arm64/kernel/cpu_errata.c | 44 ++++++++++++++++++++++++++++++++++ > > > 1 file changed, 44 insertions(+) > > > > > > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c > > > index 6958dcdabf7d..172ffbabd597 100644 > > > --- a/arch/arm64/kernel/cpu_errata.c > > > +++ b/arch/arm64/kernel/cpu_errata.c > > > @@ -278,6 +278,7 @@ static int detect_harden_bp_fw(void) > > > DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required); > > > > > > int ssbd_state __read_mostly = ARM64_SSBD_KERNEL; > > > +static bool __ssb_safe = true; > > > > > > static const struct ssbd_options { > > > const char *str; > > > @@ -386,6 +387,9 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, > > > > > > WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible()); > > > > > > + if (is_midr_in_range_list(read_cpuid_id(), entry->midr_range_list)) > > > + __ssb_safe = false; > > > + > > > > Does this mean that we assume that CPUs not present in our table are not > > affected by speculative store bypass? > > No, not affected are only those where we either have SSBS or the firmware > explicitly returns SMCCC_RET_NOT_REQUIRED. This is governed by ssbd_state. > So this doesn't affect correctness. I don't think that's true. My TX2, for example, says "Not affected" for spec_store_bypass, but we don't actually know whether it's affected or not and so it should report "Vulnerable" instead, like we do for spectre_v2 on the same machine. > __ssb_safe is an additional state just used for the sysfs output. But > indeed it looks like this is wrong if the CPU is both not listed and the > system doesn't provide the firmware interface: AFAICS we would report "Not > affected" in this case. Yes, that's what I was getting at. > > I don't think that's a good > > assumption, because we don't necessary have knowledge about partner or > > future CPU implementations, so I think any CPU lists really have to be > > whitelists like they are for the other vulnerabilities. > > I think the idea was to cover all those "legacy" systems which have > older cores (no SSBS), but didn't get an firmware update. So your old Seattle > would truthfully report "Vulnerable", but any random A53 device would > report "Not affected", even with ancient firmware. The only manageable way to deal with this is to use a whitelist, just like we do for the other vulnerabilities. We shouldn't have to update it for long because newer cores should have SSBS. Will
On Fri, 5 Apr 2019 15:43:10 +0100 Will Deacon <will.deacon@arm.com> wrote: > On Fri, Apr 05, 2019 at 11:10:22AM +0100, Andre Przywara wrote: > > On Wed, 3 Apr 2019 17:50:05 +0100 > > Will Deacon <will.deacon@arm.com> wrote: > > > > > Hi Jeremy, > > > > > > On Thu, Mar 21, 2019 at 06:05:56PM -0500, Jeremy Linton wrote: > > > > Return status based on ssbd_state and the arm64 SSBS feature. If > > > > the mitigation is disabled, or the firmware isn't responding then > > > > return the expected machine state based on a new blacklist of known > > > > vulnerable cores. > > > > > > > > Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> > > > > Reviewed-by: Andre Przywara <andre.przywara@arm.com> > > > > Tested-by: Stefan Wahren <stefan.wahren@i2se.com> > > > > --- > > > > arch/arm64/kernel/cpu_errata.c | 44 ++++++++++++++++++++++++++++++++++ > > > > 1 file changed, 44 insertions(+) > > > > > > > > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c > > > > index 6958dcdabf7d..172ffbabd597 100644 > > > > --- a/arch/arm64/kernel/cpu_errata.c > > > > +++ b/arch/arm64/kernel/cpu_errata.c > > > > @@ -278,6 +278,7 @@ static int detect_harden_bp_fw(void) > > > > DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required); > > > > > > > > int ssbd_state __read_mostly = ARM64_SSBD_KERNEL; > > > > +static bool __ssb_safe = true; > > > > > > > > static const struct ssbd_options { > > > > const char *str; > > > > @@ -386,6 +387,9 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, > > > > > > > > WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible()); > > > > > > > > + if (is_midr_in_range_list(read_cpuid_id(), entry->midr_range_list)) > > > > + __ssb_safe = false; > > > > + > > > > > > Does this mean that we assume that CPUs not present in our table are not > > > affected by speculative store bypass? > > > > No, not affected are only those where we either have SSBS or the firmware > > explicitly returns SMCCC_RET_NOT_REQUIRED. This is governed by ssbd_state. > > So this doesn't affect correctness. > > I don't think that's true. My TX2, for example, says "Not affected" for > spec_store_bypass, but we don't actually know whether it's affected or > not and so it should report "Vulnerable" instead, like we do for spectre_v2 > on the same machine. Yeah, what I actually meant was that this list doesn't affect whether the workaround gets applied or not. But indeed the reporting is wrong. > > __ssb_safe is an additional state just used for the sysfs output. But > > indeed it looks like this is wrong if the CPU is both not listed and the > > system doesn't provide the firmware interface: AFAICS we would report "Not > > affected" in this case. > > Yes, that's what I was getting at. > > > > I don't think that's a good > > > assumption, because we don't necessary have knowledge about partner or > > > future CPU implementations, so I think any CPU lists really have to be > > > whitelists like they are for the other vulnerabilities. > > > > I think the idea was to cover all those "legacy" systems which have > > older cores (no SSBS), but didn't get an firmware update. So your old Seattle > > would truthfully report "Vulnerable", but any random A53 device would > > report "Not affected", even with ancient firmware. > > The only manageable way to deal with this is to use a whitelist, just like > we do for the other vulnerabilities. We shouldn't have to update it for > long because newer cores should have SSBS. Agreed. We should start with __ssb_safe = false, and work from there. Seems much safer. Cheers, Andre.
Hi, On 4/5/19 10:18 AM, Andre Przywara wrote: > On Fri, 5 Apr 2019 15:43:10 +0100 > Will Deacon <will.deacon@arm.com> wrote: > >> On Fri, Apr 05, 2019 at 11:10:22AM +0100, Andre Przywara wrote: >>> On Wed, 3 Apr 2019 17:50:05 +0100 >>> Will Deacon <will.deacon@arm.com> wrote: >>> >>>> Hi Jeremy, >>>> >>>> On Thu, Mar 21, 2019 at 06:05:56PM -0500, Jeremy Linton wrote: >>>>> Return status based on ssbd_state and the arm64 SSBS feature. If >>>>> the mitigation is disabled, or the firmware isn't responding then >>>>> return the expected machine state based on a new blacklist of known >>>>> vulnerable cores. >>>>> >>>>> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com> >>>>> Reviewed-by: Andre Przywara <andre.przywara@arm.com> >>>>> Tested-by: Stefan Wahren <stefan.wahren@i2se.com> >>>>> --- >>>>> arch/arm64/kernel/cpu_errata.c | 44 ++++++++++++++++++++++++++++++++++ >>>>> 1 file changed, 44 insertions(+) >>>>> >>>>> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c >>>>> index 6958dcdabf7d..172ffbabd597 100644 >>>>> --- a/arch/arm64/kernel/cpu_errata.c >>>>> +++ b/arch/arm64/kernel/cpu_errata.c >>>>> @@ -278,6 +278,7 @@ static int detect_harden_bp_fw(void) >>>>> DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required); >>>>> >>>>> int ssbd_state __read_mostly = ARM64_SSBD_KERNEL; >>>>> +static bool __ssb_safe = true; >>>>> >>>>> static const struct ssbd_options { >>>>> const char *str; >>>>> @@ -386,6 +387,9 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, >>>>> >>>>> WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible()); >>>>> >>>>> + if (is_midr_in_range_list(read_cpuid_id(), entry->midr_range_list)) >>>>> + __ssb_safe = false; >>>>> + >>>> >>>> Does this mean that we assume that CPUs not present in our table are not >>>> affected by speculative store bypass? >>> >>> No, not affected are only those where we either have SSBS or the firmware >>> explicitly returns SMCCC_RET_NOT_REQUIRED. This is governed by ssbd_state. >>> So this doesn't affect correctness. >> >> I don't think that's true. My TX2, for example, says "Not affected" for >> spec_store_bypass, but we don't actually know whether it's affected or >> not and so it should report "Vulnerable" instead, like we do for spectre_v2 >> on the same machine. > > Yeah, what I actually meant was that this list doesn't affect whether the workaround gets applied or not. But indeed the reporting is wrong. > >>> __ssb_safe is an additional state just used for the sysfs output. But >>> indeed it looks like this is wrong if the CPU is both not listed and the >>> system doesn't provide the firmware interface: AFAICS we would report "Not >>> affected" in this case. >> >> Yes, that's what I was getting at. >> >>>> I don't think that's a good >>>> assumption, because we don't necessary have knowledge about partner or >>>> future CPU implementations, so I think any CPU lists really have to be >>>> whitelists like they are for the other vulnerabilities. >>> >>> I think the idea was to cover all those "legacy" systems which have >>> older cores (no SSBS), but didn't get an firmware update. So your old Seattle >>> would truthfully report "Vulnerable", but any random A53 device would >>> report "Not affected", even with ancient firmware. >> >> The only manageable way to deal with this is to use a whitelist, just like >> we do for the other vulnerabilities. We shouldn't have to update it for >> long because newer cores should have SSBS. > > Agreed. We should start with __ssb_safe = false, and work from there. Seems much safer. I tended to view this with a more charitable view (aka vendors with vulnerable machines would have put the effort in to get their firmware working). But that does violate the "if you don't know, its vulnerable" statements made earlier. I guess the advantage of claiming machines are vulnerable which aren't is that it strongly encourages vendors which are not vulnerable to come out and say so. I will invert this logic and repost in the next day or so. Thanks,
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c index 6958dcdabf7d..172ffbabd597 100644 --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -278,6 +278,7 @@ static int detect_harden_bp_fw(void) DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required); int ssbd_state __read_mostly = ARM64_SSBD_KERNEL; +static bool __ssb_safe = true; static const struct ssbd_options { const char *str; @@ -386,6 +387,9 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible()); + if (is_midr_in_range_list(read_cpuid_id(), entry->midr_range_list)) + __ssb_safe = false; + if (this_cpu_has_cap(ARM64_SSBS)) { required = false; goto out_printmsg; @@ -419,12 +423,14 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, ssbd_state = ARM64_SSBD_UNKNOWN; return false; + /* machines with mixed mitigation requirements must not return this */ case SMCCC_RET_NOT_REQUIRED: pr_info_once("%s mitigation not required\n", entry->desc); ssbd_state = ARM64_SSBD_MITIGATED; return false; case SMCCC_RET_SUCCESS: + __ssb_safe = false; required = true; break; @@ -474,6 +480,16 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry, return required; } +/* known vulnerable cores */ +static const struct midr_range arm64_ssb_cpus[] = { + MIDR_ALL_VERSIONS(MIDR_CORTEX_A57), + MIDR_ALL_VERSIONS(MIDR_CORTEX_A72), + MIDR_ALL_VERSIONS(MIDR_CORTEX_A73), + MIDR_ALL_VERSIONS(MIDR_CORTEX_A75), + MIDR_ALL_VERSIONS(MIDR_CORTEX_A76), + {}, +}; + static void __maybe_unused cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused) { @@ -769,6 +785,7 @@ const struct arm64_cpu_capabilities arm64_errata[] = { .capability = ARM64_SSBD, .type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM, .matches = has_ssbd_mitigation, + .midr_range_list = arm64_ssb_cpus, }, #ifdef CONFIG_ARM64_ERRATUM_1188873 { @@ -807,3 +824,30 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, return sprintf(buf, "Vulnerable\n"); } + +ssize_t cpu_show_spec_store_bypass(struct device *dev, + struct device_attribute *attr, char *buf) +{ + /* + * Two assumptions: First, ssbd_state reflects the worse case + * for heterogeneous machines, and that if SSBS is supported its + * supported by all cores. + */ + switch (ssbd_state) { + case ARM64_SSBD_MITIGATED: + return sprintf(buf, "Not affected\n"); + + case ARM64_SSBD_KERNEL: + case ARM64_SSBD_FORCE_ENABLE: + if (cpus_have_cap(ARM64_SSBS)) + return sprintf(buf, "Not affected\n"); + if (IS_ENABLED(CONFIG_ARM64_SSBD)) + return sprintf(buf, + "Mitigation: Speculative Store Bypass disabled\n"); + } + + if (__ssb_safe) + return sprintf(buf, "Not affected\n"); + + return sprintf(buf, "Vulnerable\n"); +}