4.17-stable review patch. If anyone has any objections, please let me know.
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From: Marc Zyngier marc.zyngier@arm.com
commit a43ae4dfe56a01f5b98ba0cb2f784b6a43bafcc6 upstream.
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.
Reviewed-by: Julien Grall julien.grall@arm.com Reviewed-by: Mark Rutland mark.rutland@arm.com Acked-by: Will Deacon will.deacon@arm.com Signed-off-by: Marc Zyngier marc.zyngier@arm.com Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Documentation/admin-guide/kernel-parameters.txt | 17 +++ arch/arm64/include/asm/cpufeature.h | 6 + arch/arm64/kernel/cpu_errata.c | 103 ++++++++++++++++++++---- 3 files changed, 110 insertions(+), 16 deletions(-)
--- 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: Unconditionally enable mitigation for + for both kernel and userspace + force-off: Unconditionally 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 --- 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_KERNEL 1 +#define ARM64_SSBD_FORCE_ENABLE 2 +#define ARM64_SSBD_MITIGATED 3 + #endif /* __ASSEMBLY__ */
#endif --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -235,6 +235,38 @@ enable_smccc_arch_workaround_1(const str #ifdef CONFIG_ARM64_SSBD DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required);
+int ssbd_state __read_mostly = ARM64_SSBD_KERNEL; + +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_KERNEL, }, +}; + +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) @@ -278,44 +310,83 @@ static bool has_ssbd_mitigation(const st 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; + } + + val = (s32)res.a0; + + switch (val) { + case SMCCC_RET_NOT_SUPPORTED: + ssbd_state = ARM64_SSBD_UNKNOWN; + return false; + + 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: + required = true; + break; + + case 1: /* Mitigation not required on this CPU */ + required = false; + break; + + default: + WARN_ON(1); + return false; }
- if (supported) { - __this_cpu_write(arm64_ssbd_callback_required, 1); + switch (ssbd_state) { + case ARM64_SSBD_FORCE_DISABLE: + pr_info_once("%s disabled from command-line\n", entry->desc); + arm64_set_ssbd_mitigation(false); + required = false; + break; + + case ARM64_SSBD_KERNEL: + if (required) { + __this_cpu_write(arm64_ssbd_callback_required, 1); + arm64_set_ssbd_mitigation(true); + } + break; + + case ARM64_SSBD_FORCE_ENABLE: + pr_info_once("%s forced from command-line\n", entry->desc); arm64_set_ssbd_mitigation(true); + required = true; + break; + + default: + WARN_ON(1); + break; }
- return supported; + return required; } #endif /* CONFIG_ARM64_SSBD */