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// SPDX-License-Identifier: GPL-2.0-only
/*
* Handle detection, reporting and mitigation of Spectre v1, v2, v3a and v4, as
* detailed at:
*
* https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability
*
* This code was originally written hastily under an awful lot of stress and so
* aspects of it are somewhat hacky. Unfortunately, changing anything in here
* instantly makes me feel ill. Thanks, Jann. Thann.
*
* Copyright (C) 2018 ARM Ltd, All Rights Reserved.
* Copyright (C) 2020 Google LLC
*
* "If there's something strange in your neighbourhood, who you gonna call?"
*
* Authors: Will Deacon <will@kernel.org> and Marc Zyngier <maz@kernel.org>
*/
#include <linux/arm-smccc.h>
#include <linux/cpu.h>
#include <linux/device.h>
#include <linux/nospec.h>
#include <linux/prctl.h>
#include <linux/sched/task_stack.h>
#include <asm/insn.h>
#include <asm/spectre.h>
#include <asm/traps.h>
#include <asm/virt.h>
/*
* We try to ensure that the mitigation state can never change as the result of
* onlining a late CPU.
*/
static void update_mitigation_state(enum mitigation_state *oldp,
enum mitigation_state new)
{
enum mitigation_state state;
do {
state = READ_ONCE(*oldp);
if (new <= state)
break;
/* Userspace almost certainly can't deal with this. */
if (WARN_ON(system_capabilities_finalized()))
break;
} while (cmpxchg_relaxed(oldp, state, new) != state);
}
/*
* Spectre v1.
*
* The kernel can't protect userspace for this one: it's each person for
* themselves. Advertise what we're doing and be done with it.
*/
ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr,
char *buf)
{
return sprintf(buf, "Mitigation: __user pointer sanitization\n");
}
/*
* Spectre v2.
*
* This one sucks. A CPU is either:
*
* - Mitigated in hardware and advertised by ID_AA64PFR0_EL1.CSV2.
* - Mitigated in hardware and listed in our "safe list".
* - Mitigated in software by firmware.
* - Mitigated in software by a CPU-specific dance in the kernel and a
* firmware call at EL2.
* - Vulnerable.
*
* It's not unlikely for different CPUs in a big.LITTLE system to fall into
* different camps.
*/
static enum mitigation_state spectre_v2_state;
static bool __read_mostly __nospectre_v2;
static int __init parse_spectre_v2_param(char *str)
{
__nospectre_v2 = true;
return 0;
}
early_param("nospectre_v2", parse_spectre_v2_param);
static bool spectre_v2_mitigations_off(void)
{
bool ret = __nospectre_v2 || cpu_mitigations_off();
if (ret)
pr_info_once("spectre-v2 mitigation disabled by command line option\n");
return ret;
}
ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
char *buf)
{
switch (spectre_v2_state) {
case SPECTRE_UNAFFECTED:
return sprintf(buf, "Not affected\n");
case SPECTRE_MITIGATED:
return sprintf(buf, "Mitigation: Branch predictor hardening\n");
case SPECTRE_VULNERABLE:
fallthrough;
default:
return sprintf(buf, "Vulnerable\n");
}
}
static enum mitigation_state spectre_v2_get_cpu_hw_mitigation_state(void)
{
u64 pfr0;
static const struct midr_range spectre_v2_safe_list[] = {
MIDR_ALL_VERSIONS(MIDR_CORTEX_A35),
MIDR_ALL_VERSIONS(MIDR_CORTEX_A53),
MIDR_ALL_VERSIONS(MIDR_CORTEX_A55),
MIDR_ALL_VERSIONS(MIDR_BRAHMA_B53),
MIDR_ALL_VERSIONS(MIDR_HISI_TSV110),
MIDR_ALL_VERSIONS(MIDR_QCOM_KRYO_2XX_SILVER),
MIDR_ALL_VERSIONS(MIDR_QCOM_KRYO_3XX_SILVER),
MIDR_ALL_VERSIONS(MIDR_QCOM_KRYO_4XX_SILVER),
{ /* sentinel */ }
};
/* If the CPU has CSV2 set, we're safe */
pfr0 = read_cpuid(ID_AA64PFR0_EL1);
if (cpuid_feature_extract_unsigned_field(pfr0, ID_AA64PFR0_CSV2_SHIFT))
return SPECTRE_UNAFFECTED;
/* Alternatively, we have a list of unaffected CPUs */
if (is_midr_in_range_list(read_cpuid_id(), spectre_v2_safe_list))
return SPECTRE_UNAFFECTED;
return SPECTRE_VULNERABLE;
}
static enum mitigation_state spectre_v2_get_cpu_fw_mitigation_state(void)
{
int ret;
struct arm_smccc_res res;
arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
ARM_SMCCC_ARCH_WORKAROUND_1, &res);
ret = res.a0;
switch (ret) {
case SMCCC_RET_SUCCESS:
return SPECTRE_MITIGATED;
case SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED:
return SPECTRE_UNAFFECTED;
default:
fallthrough;
case SMCCC_RET_NOT_SUPPORTED:
return SPECTRE_VULNERABLE;
}
}
bool has_spectre_v2(const struct arm64_cpu_capabilities *entry, int scope)
{
WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
if (spectre_v2_get_cpu_hw_mitigation_state() == SPECTRE_UNAFFECTED)
return false;
if (spectre_v2_get_cpu_fw_mitigation_state() == SPECTRE_UNAFFECTED)
return false;
return true;
}
enum mitigation_state arm64_get_spectre_v2_state(void)
{
return spectre_v2_state;
}
DEFINE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data);
static void install_bp_hardening_cb(bp_hardening_cb_t fn)
{
__this_cpu_write(bp_hardening_data.fn, fn);
/*
* Vinz Clortho takes the hyp_vecs start/end "keys" at
* the door when we're a guest. Skip the hyp-vectors work.
*/
if (!is_hyp_mode_available())
return;
__this_cpu_write(bp_hardening_data.slot, HYP_VECTOR_SPECTRE_DIRECT);
}
static void call_smc_arch_workaround_1(void)
{
arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_1, NULL);
}
static void call_hvc_arch_workaround_1(void)
{
arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_WORKAROUND_1, NULL);
}
static void qcom_link_stack_sanitisation(void)
{
u64 tmp;
asm volatile("mov %0, x30 \n"
".rept 16 \n"
"bl . + 4 \n"
".endr \n"
"mov x30, %0 \n"
: "=&r" (tmp));
}
static bp_hardening_cb_t spectre_v2_get_sw_mitigation_cb(void)
{
u32 midr = read_cpuid_id();
if (((midr & MIDR_CPU_MODEL_MASK) != MIDR_QCOM_FALKOR) &&
((midr & MIDR_CPU_MODEL_MASK) != MIDR_QCOM_FALKOR_V1))
return NULL;
return qcom_link_stack_sanitisation;
}
static enum mitigation_state spectre_v2_enable_fw_mitigation(void)
{
bp_hardening_cb_t cb;
enum mitigation_state state;
state = spectre_v2_get_cpu_fw_mitigation_state();
if (state != SPECTRE_MITIGATED)
return state;
if (spectre_v2_mitigations_off())
return SPECTRE_VULNERABLE;
switch (arm_smccc_1_1_get_conduit()) {
case SMCCC_CONDUIT_HVC:
cb = call_hvc_arch_workaround_1;
break;
case SMCCC_CONDUIT_SMC:
cb = call_smc_arch_workaround_1;
break;
default:
return SPECTRE_VULNERABLE;
}
/*
* Prefer a CPU-specific workaround if it exists. Note that we
* still rely on firmware for the mitigation at EL2.
*/
cb = spectre_v2_get_sw_mitigation_cb() ?: cb;
install_bp_hardening_cb(cb);
return SPECTRE_MITIGATED;
}
void spectre_v2_enable_mitigation(const struct arm64_cpu_capabilities *__unused)
{
enum mitigation_state state;
WARN_ON(preemptible());
state = spectre_v2_get_cpu_hw_mitigation_state();
if (state == SPECTRE_VULNERABLE)
state = spectre_v2_enable_fw_mitigation();
update_mitigation_state(&spectre_v2_state, state);
}
/*
* Spectre-v3a.
*
* Phew, there's not an awful lot to do here! We just instruct EL2 to use
* an indirect trampoline for the hyp vectors so that guests can't read
* VBAR_EL2 to defeat randomisation of the hypervisor VA layout.
*/
bool has_spectre_v3a(const struct arm64_cpu_capabilities *entry, int scope)
{
static const struct midr_range spectre_v3a_unsafe_list[] = {
MIDR_ALL_VERSIONS(MIDR_CORTEX_A57),
MIDR_ALL_VERSIONS(MIDR_CORTEX_A72),
{},
};
WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
return is_midr_in_range_list(read_cpuid_id(), spectre_v3a_unsafe_list);
}
void spectre_v3a_enable_mitigation(const struct arm64_cpu_capabilities *__unused)
{
struct bp_hardening_data *data = this_cpu_ptr(&bp_hardening_data);
if (this_cpu_has_cap(ARM64_SPECTRE_V3A))
data->slot += HYP_VECTOR_INDIRECT;
}
/*
* Spectre v4.
*
* If you thought Spectre v2 was nasty, wait until you see this mess. A CPU is
* either:
*
* - Mitigated in hardware and listed in our "safe list".
* - Mitigated in hardware via PSTATE.SSBS.
* - Mitigated in software by firmware (sometimes referred to as SSBD).
*
* Wait, that doesn't sound so bad, does it? Keep reading...
*
* A major source of headaches is that the software mitigation is enabled both
* on a per-task basis, but can also be forced on for the kernel, necessitating
* both context-switch *and* entry/exit hooks. To make it even worse, some CPUs
* allow EL0 to toggle SSBS directly, which can end up with the prctl() state
* being stale when re-entering the kernel. The usual big.LITTLE caveats apply,
* so you can have systems that have both firmware and SSBS mitigations. This
* means we actually have to reject late onlining of CPUs with mitigations if
* all of the currently onlined CPUs are safelisted, as the mitigation tends to
* be opt-in for userspace. Yes, really, the cure is worse than the disease.
*
* The only good part is that if the firmware mitigation is present, then it is
* present for all CPUs, meaning we don't have to worry about late onlining of a
* vulnerable CPU if one of the boot CPUs is using the firmware mitigation.
*
* Give me a VAX-11/780 any day of the week...
*/
static enum mitigation_state spectre_v4_state;
/* This is the per-cpu state tracking whether we need to talk to firmware */
DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required);
enum spectre_v4_policy {
SPECTRE_V4_POLICY_MITIGATION_DYNAMIC,
SPECTRE_V4_POLICY_MITIGATION_ENABLED,
SPECTRE_V4_POLICY_MITIGATION_DISABLED,
};
static enum spectre_v4_policy __read_mostly __spectre_v4_policy;
static const struct spectre_v4_param {
const char *str;
enum spectre_v4_policy policy;
} spectre_v4_params[] = {
{ "force-on", SPECTRE_V4_POLICY_MITIGATION_ENABLED, },
{ "force-off", SPECTRE_V4_POLICY_MITIGATION_DISABLED, },
{ "kernel", SPECTRE_V4_POLICY_MITIGATION_DYNAMIC, },
};
static int __init parse_spectre_v4_param(char *str)
{
int i;
if (!str || !str[0])
return -EINVAL;
for (i = 0; i < ARRAY_SIZE(spectre_v4_params); i++) {
const struct spectre_v4_param *param = &spectre_v4_params[i];
if (strncmp(str, param->str, strlen(param->str)))
continue;
__spectre_v4_policy = param->policy;
return 0;
}
return -EINVAL;
}
early_param("ssbd", parse_spectre_v4_param);
/*
* Because this was all written in a rush by people working in different silos,
* we've ended up with multiple command line options to control the same thing.
* Wrap these up in some helpers, which prefer disabling the mitigation if faced
* with contradictory parameters. The mitigation is always either "off",
* "dynamic" or "on".
*/
static bool spectre_v4_mitigations_off(void)
{
bool ret = cpu_mitigations_off() ||
__spectre_v4_policy == SPECTRE_V4_POLICY_MITIGATION_DISABLED;
if (ret)
pr_info_once("spectre-v4 mitigation disabled by command-line option\n");
return ret;
}
/* Do we need to toggle the mitigation state on entry to/exit from the kernel? */
static bool spectre_v4_mitigations_dynamic(void)
{
return !spectre_v4_mitigations_off() &&
__spectre_v4_policy == SPECTRE_V4_POLICY_MITIGATION_DYNAMIC;
}
static bool spectre_v4_mitigations_on(void)
{
return !spectre_v4_mitigations_off() &&
__spectre_v4_policy == SPECTRE_V4_POLICY_MITIGATION_ENABLED;
}
ssize_t cpu_show_spec_store_bypass(struct device *dev,
struct device_attribute *attr, char *buf)
{
switch (spectre_v4_state) {
case SPECTRE_UNAFFECTED:
return sprintf(buf, "Not affected\n");
case SPECTRE_MITIGATED:
return sprintf(buf, "Mitigation: Speculative Store Bypass disabled via prctl\n");
case SPECTRE_VULNERABLE:
fallthrough;
default:
return sprintf(buf, "Vulnerable\n");
}
}
enum mitigation_state arm64_get_spectre_v4_state(void)
{
return spectre_v4_state;
}
static enum mitigation_state spectre_v4_get_cpu_hw_mitigation_state(void)
{
static const struct midr_range spectre_v4_safe_list[] = {
MIDR_ALL_VERSIONS(MIDR_CORTEX_A35),
MIDR_ALL_VERSIONS(MIDR_CORTEX_A53),
MIDR_ALL_VERSIONS(MIDR_CORTEX_A55),
MIDR_ALL_VERSIONS(MIDR_BRAHMA_B53),
MIDR_ALL_VERSIONS(MIDR_QCOM_KRYO_3XX_SILVER),
MIDR_ALL_VERSIONS(MIDR_QCOM_KRYO_4XX_SILVER),
{ /* sentinel */ },
};
if (is_midr_in_range_list(read_cpuid_id(), spectre_v4_safe_list))
return SPECTRE_UNAFFECTED;
/* CPU features are detected first */
if (this_cpu_has_cap(ARM64_SSBS))
return SPECTRE_MITIGATED;
return SPECTRE_VULNERABLE;
}
static enum mitigation_state spectre_v4_get_cpu_fw_mitigation_state(void)
{
int ret;
struct arm_smccc_res res;
arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
ARM_SMCCC_ARCH_WORKAROUND_2, &res);
ret = res.a0;
switch (ret) {
case SMCCC_RET_SUCCESS:
return SPECTRE_MITIGATED;
case SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED:
fallthrough;
case SMCCC_RET_NOT_REQUIRED:
return SPECTRE_UNAFFECTED;
default:
fallthrough;
case SMCCC_RET_NOT_SUPPORTED:
return SPECTRE_VULNERABLE;
}
}
bool has_spectre_v4(const struct arm64_cpu_capabilities *cap, int scope)
{
enum mitigation_state state;
WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
state = spectre_v4_get_cpu_hw_mitigation_state();
if (state == SPECTRE_VULNERABLE)
state = spectre_v4_get_cpu_fw_mitigation_state();
return state != SPECTRE_UNAFFECTED;
}
static int ssbs_emulation_handler(struct pt_regs *regs, u32 instr)
{
if (user_mode(regs))
return 1;
if (instr & BIT(PSTATE_Imm_shift))
regs->pstate |= PSR_SSBS_BIT;
else
regs->pstate &= ~PSR_SSBS_BIT;
arm64_skip_faulting_instruction(regs, 4);
return 0;
}
static struct undef_hook ssbs_emulation_hook = {
.instr_mask = ~(1U << PSTATE_Imm_shift),
.instr_val = 0xd500401f | PSTATE_SSBS,
.fn = ssbs_emulation_handler,
};
static enum mitigation_state spectre_v4_enable_hw_mitigation(void)
{
static bool undef_hook_registered = false;
static DEFINE_RAW_SPINLOCK(hook_lock);
enum mitigation_state state;
/*
* If the system is mitigated but this CPU doesn't have SSBS, then
* we must be on the safelist and there's nothing more to do.
*/
state = spectre_v4_get_cpu_hw_mitigation_state();
if (state != SPECTRE_MITIGATED || !this_cpu_has_cap(ARM64_SSBS))
return state;
raw_spin_lock(&hook_lock);
if (!undef_hook_registered) {
register_undef_hook(&ssbs_emulation_hook);
undef_hook_registered = true;
}
raw_spin_unlock(&hook_lock);
if (spectre_v4_mitigations_off()) {
sysreg_clear_set(sctlr_el1, 0, SCTLR_ELx_DSSBS);
set_pstate_ssbs(1);
return SPECTRE_VULNERABLE;
}
/* SCTLR_EL1.DSSBS was initialised to 0 during boot */
set_pstate_ssbs(0);
return SPECTRE_MITIGATED;
}
/*
* Patch a branch over the Spectre-v4 mitigation code with a NOP so that
* we fallthrough and check whether firmware needs to be called on this CPU.
*/
void __init spectre_v4_patch_fw_mitigation_enable(struct alt_instr *alt,
__le32 *origptr,
__le32 *updptr, int nr_inst)
{
BUG_ON(nr_inst != 1); /* Branch -> NOP */
if (spectre_v4_mitigations_off())
return;
if (cpus_have_final_cap(ARM64_SSBS))
return;
if (spectre_v4_mitigations_dynamic())
*updptr = cpu_to_le32(aarch64_insn_gen_nop());
}
/*
* Patch a NOP in the Spectre-v4 mitigation code with an SMC/HVC instruction
* to call into firmware to adjust the mitigation state.
*/
void __init spectre_v4_patch_fw_mitigation_conduit(struct alt_instr *alt,
__le32 *origptr,
__le32 *updptr, int nr_inst)
{
u32 insn;
BUG_ON(nr_inst != 1); /* NOP -> HVC/SMC */
switch (arm_smccc_1_1_get_conduit()) {
case SMCCC_CONDUIT_HVC:
insn = aarch64_insn_get_hvc_value();
break;
case SMCCC_CONDUIT_SMC:
insn = aarch64_insn_get_smc_value();
break;
default:
return;
}
*updptr = cpu_to_le32(insn);
}
static enum mitigation_state spectre_v4_enable_fw_mitigation(void)
{
enum mitigation_state state;
state = spectre_v4_get_cpu_fw_mitigation_state();
if (state != SPECTRE_MITIGATED)
return state;
if (spectre_v4_mitigations_off()) {
arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_WORKAROUND_2, false, NULL);
return SPECTRE_VULNERABLE;
}
arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_WORKAROUND_2, true, NULL);
if (spectre_v4_mitigations_dynamic())
__this_cpu_write(arm64_ssbd_callback_required, 1);
return SPECTRE_MITIGATED;
}
void spectre_v4_enable_mitigation(const struct arm64_cpu_capabilities *__unused)
{
enum mitigation_state state;
WARN_ON(preemptible());
state = spectre_v4_enable_hw_mitigation();
if (state == SPECTRE_VULNERABLE)
state = spectre_v4_enable_fw_mitigation();
update_mitigation_state(&spectre_v4_state, state);
}
static void __update_pstate_ssbs(struct pt_regs *regs, bool state)
{
u64 bit = compat_user_mode(regs) ? PSR_AA32_SSBS_BIT : PSR_SSBS_BIT;
if (state)
regs->pstate |= bit;
else
regs->pstate &= ~bit;
}
void spectre_v4_enable_task_mitigation(struct task_struct *tsk)
{
struct pt_regs *regs = task_pt_regs(tsk);
bool ssbs = false, kthread = tsk->flags & PF_KTHREAD;
if (spectre_v4_mitigations_off())
ssbs = true;
else if (spectre_v4_mitigations_dynamic() && !kthread)
ssbs = !test_tsk_thread_flag(tsk, TIF_SSBD);
__update_pstate_ssbs(regs, ssbs);
}
/*
* The Spectre-v4 mitigation can be controlled via a prctl() from userspace.
* This is interesting because the "speculation disabled" behaviour can be
* configured so that it is preserved across exec(), which means that the
* prctl() may be necessary even when PSTATE.SSBS can be toggled directly
* from userspace.
*/
static void ssbd_prctl_enable_mitigation(struct task_struct *task)
{
task_clear_spec_ssb_noexec(task);
task_set_spec_ssb_disable(task);
set_tsk_thread_flag(task, TIF_SSBD);
}
static void ssbd_prctl_disable_mitigation(struct task_struct *task)
{
task_clear_spec_ssb_noexec(task);
task_clear_spec_ssb_disable(task);
clear_tsk_thread_flag(task, TIF_SSBD);
}
static int ssbd_prctl_set(struct task_struct *task, unsigned long ctrl)
{
switch (ctrl) {
case PR_SPEC_ENABLE:
/* Enable speculation: disable mitigation */
/*
* Force disabled speculation prevents it from being
* re-enabled.
*/
if (task_spec_ssb_force_disable(task))
return -EPERM;
/*
* If the mitigation is forced on, then speculation is forced
* off and we again prevent it from being re-enabled.
*/
if (spectre_v4_mitigations_on())
return -EPERM;
ssbd_prctl_disable_mitigation(task);
break;
case PR_SPEC_FORCE_DISABLE:
/* Force disable speculation: force enable mitigation */
/*
* If the mitigation is forced off, then speculation is forced
* on and we prevent it from being disabled.
*/
if (spectre_v4_mitigations_off())
return -EPERM;
task_set_spec_ssb_force_disable(task);
fallthrough;
case PR_SPEC_DISABLE:
/* Disable speculation: enable mitigation */
/* Same as PR_SPEC_FORCE_DISABLE */
if (spectre_v4_mitigations_off())
return -EPERM;
ssbd_prctl_enable_mitigation(task);
break;
case PR_SPEC_DISABLE_NOEXEC:
/* Disable speculation until execve(): enable mitigation */
/*
* If the mitigation state is forced one way or the other, then
* we must fail now before we try to toggle it on execve().
*/
if (task_spec_ssb_force_disable(task) ||
spectre_v4_mitigations_off() ||
spectre_v4_mitigations_on()) {
return -EPERM;
}
ssbd_prctl_enable_mitigation(task);
task_set_spec_ssb_noexec(task);
break;
default:
return -ERANGE;
}
spectre_v4_enable_task_mitigation(task);
return 0;
}
int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
unsigned long ctrl)
{
switch (which) {
case PR_SPEC_STORE_BYPASS:
return ssbd_prctl_set(task, ctrl);
default:
return -ENODEV;
}
}
static int ssbd_prctl_get(struct task_struct *task)
{
switch (spectre_v4_state) {
case SPECTRE_UNAFFECTED:
return PR_SPEC_NOT_AFFECTED;
case SPECTRE_MITIGATED:
if (spectre_v4_mitigations_on())
return PR_SPEC_NOT_AFFECTED;
if (spectre_v4_mitigations_dynamic())
break;
/* Mitigations are disabled, so we're vulnerable. */
fallthrough;
case SPECTRE_VULNERABLE:
fallthrough;
default:
return PR_SPEC_ENABLE;
}
/* Check the mitigation state for this task */
if (task_spec_ssb_force_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;
if (task_spec_ssb_noexec(task))
return PR_SPEC_PRCTL | PR_SPEC_DISABLE_NOEXEC;
if (task_spec_ssb_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
}
int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
{
switch (which) {
case PR_SPEC_STORE_BYPASS:
return ssbd_prctl_get(task);
default:
return -ENODEV;
}
}