On Tue, May 22, 2018 at 04:06:39PM +0100, Marc Zyngier wrote: > On a system where the firmware implements ARCH_WORKAROUND_2, > it may be useful to either permanently enable or disable the > workaround for cases where the user decides that they'd rather > not get a trap overhead, and keep the mitigation permanently > on or off instead of switching it on exception entry/exit. > > In any case, default to the mitigation being enabled. > > Signed-off-by: Marc Zyngier <marc.zyng...@arm.com> > --- > Documentation/admin-guide/kernel-parameters.txt | 17 ++++ > arch/arm64/include/asm/cpufeature.h | 6 ++ > arch/arm64/kernel/cpu_errata.c | 102 > ++++++++++++++++++++---- > 3 files changed, 109 insertions(+), 16 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt > b/Documentation/admin-guide/kernel-parameters.txt > index f2040d46f095..646e112c6f63 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -4092,6 +4092,23 @@ > expediting. Set to zero to disable automatic > expediting. > > + ssbd= [ARM64,HW] > + Speculative Store Bypass Disable control > + > + On CPUs that are vulnerable to the Speculative > + Store Bypass vulnerability and offer a > + firmware based mitigation, this parameter > + indicates how the mitigation should be used: > + > + force-on: Unconditionnaly enable mitigation for > + for both kernel and userspace > + force-off: Unconditionnaly disable mitigation for > + for both kernel and userspace > + kernel: Always enable mitigation in the > + kernel, and offer a prctl interface > + to allow userspace to register its > + interest in being mitigated too. > + > stack_guard_gap= [MM] > override the default stack gap protection. The value > is in page units and it defines how many pages prior > diff --git a/arch/arm64/include/asm/cpufeature.h > b/arch/arm64/include/asm/cpufeature.h > index 09b0f2a80c8f..9bc548e22784 100644 > --- a/arch/arm64/include/asm/cpufeature.h > +++ b/arch/arm64/include/asm/cpufeature.h > @@ -537,6 +537,12 @@ static inline u64 read_zcr_features(void) > return zcr; > } > > +#define ARM64_SSBD_UNKNOWN -1 > +#define ARM64_SSBD_FORCE_DISABLE 0 > +#define ARM64_SSBD_EL1_ENTRY 1
The EL1_ENTRY part of the name is a bit misleading, since this doesn't apply to EL1->EL1 exceptions (and as with many other bits of the arm64 code, it's arguably misleading in the VHE case). Perhaps ARM64_SSBD_KERNEL, which would align with the parameter name? Not a big deal either way, and otherwise this looks good to me. Regardless: Reviewed-by: Mark Rutland <mark.rutl...@arm.com> Mark. > +#define ARM64_SSBD_FORCE_ENABLE 2 > +#define ARM64_SSBD_MITIGATED 3 > + > #endif /* __ASSEMBLY__ */ > > #endif > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c > index 7fd6d5b001f5..f1d4e75b0ddd 100644 > --- a/arch/arm64/kernel/cpu_errata.c > +++ b/arch/arm64/kernel/cpu_errata.c > @@ -235,6 +235,38 @@ enable_smccc_arch_workaround_1(const struct > arm64_cpu_capabilities *entry) > #ifdef CONFIG_ARM64_SSBD > DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required); > > +int ssbd_state __read_mostly = ARM64_SSBD_EL1_ENTRY; > + > +static const struct ssbd_options { > + const char *str; > + int state; > +} ssbd_options[] = { > + { "force-on", ARM64_SSBD_FORCE_ENABLE, }, > + { "force-off", ARM64_SSBD_FORCE_DISABLE, }, > + { "kernel", ARM64_SSBD_EL1_ENTRY, }, > +}; > + > +static int __init ssbd_cfg(char *buf) > +{ > + int i; > + > + if (!buf || !buf[0]) > + return -EINVAL; > + > + for (i = 0; i < ARRAY_SIZE(ssbd_options); i++) { > + int len = strlen(ssbd_options[i].str); > + > + if (strncmp(buf, ssbd_options[i].str, len)) > + continue; > + > + ssbd_state = ssbd_options[i].state; > + return 0; > + } > + > + return -EINVAL; > +} > +early_param("ssbd", ssbd_cfg); > + > void __init arm64_update_smccc_conduit(struct alt_instr *alt, > __le32 *origptr, __le32 *updptr, > int nr_inst) > @@ -272,44 +304,82 @@ static bool has_ssbd_mitigation(const struct > arm64_cpu_capabilities *entry, > int scope) > { > struct arm_smccc_res res; > - bool supported = true; > + bool required = true; > + s32 val; > > WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible()); > > - if (psci_ops.smccc_version == SMCCC_VERSION_1_0) > + if (psci_ops.smccc_version == SMCCC_VERSION_1_0) { > + ssbd_state = ARM64_SSBD_UNKNOWN; > return false; > + } > > - /* > - * The probe function return value is either negative > - * (unsupported or mitigated), positive (unaffected), or zero > - * (requires mitigation). We only need to do anything in the > - * last case. > - */ > switch (psci_ops.conduit) { > case PSCI_CONDUIT_HVC: > arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID, > ARM_SMCCC_ARCH_WORKAROUND_2, &res); > - if ((int)res.a0 != 0) > - supported = false; > break; > > case PSCI_CONDUIT_SMC: > arm_smccc_1_1_smc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID, > ARM_SMCCC_ARCH_WORKAROUND_2, &res); > - if ((int)res.a0 != 0) > - supported = false; > break; > > default: > - supported = false; > + ssbd_state = ARM64_SSBD_UNKNOWN; > + return false; > } > > - if (supported) { > - __this_cpu_write(arm64_ssbd_callback_required, 1); > + val = (s32)res.a0; > + > + switch (val) { > + case SMCCC_RET_NOT_SUPPORTED: > + ssbd_state = ARM64_SSBD_UNKNOWN; > + return false; > + > + case SMCCC_RET_NOT_REQUIRED: > + ssbd_state = ARM64_SSBD_MITIGATED; > + return false; > + > + case SMCCC_RET_SUCCESS: > + required = true; > + break; > + > + case 1: /* Mitigation not required on this CPU */ > + required = false; > + break; > + > + default: > + WARN_ON(1); > + return false; > + } > + > + switch (ssbd_state) { > + case ARM64_SSBD_FORCE_DISABLE: > + pr_info_once("%s disabled from command-line\n", entry->desc); > + do_ssbd(false); > + required = false; > + break; > + > + case ARM64_SSBD_EL1_ENTRY: > + if (required) { > + __this_cpu_write(arm64_ssbd_callback_required, 1); > + do_ssbd(true); > + } > + break; > + > + case ARM64_SSBD_FORCE_ENABLE: > + pr_info_once("%s forced from command-line\n", entry->desc); > do_ssbd(true); > + required = true; > + break; > + > + default: > + WARN_ON(1); > + break; > } > > - return supported; > + return required; > } > #endif /* CONFIG_ARM64_SSBD */ > > -- > 2.14.2 > _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm