arm64/kernel/process.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Based on arch/arm/kernel/process.c
 *
 * Original Copyright (C) 1995  Linus Torvalds
 * Copyright (C) 1996-2000 Russell King - Converted to ARM.
 * Copyright (C) 2012 ARM Ltd.
 */

#include <stdarg.h>

#include <trace/events/power.h>
#include <linux/compat.h>
#include <linux/efi.h>
#include <linux/elf.h>
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/sched/task.h>
#include <linux/sched/task_stack.h>
#include <linux/kernel.h>
#include <linux/lockdep.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/nospec.h>
#include <linux/stddef.h>
#include <linux/sysctl.h>
#include <linux/unistd.h>
#include <linux/user.h>
#include <linux/delay.h>
#include <linux/reboot.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/cpu.h>
#include <linux/elfcore.h>
#include <linux/pm.h>
#include <linux/tick.h>
#include <linux/utsname.h>
#include <linux/uaccess.h>
#include <linux/random.h>
#include <linux/hw_breakpoint.h>
#include <linux/personality.h>
#include <linux/notifier.h>
#include <linux/percpu.h>
#include <linux/thread_info.h>
#include <linux/prctl.h>

#include <asm/alternative.h>
#include <asm/arch_gicv3.h>
#include <asm/compat.h>
#include <asm/cpufeature.h>
#include <asm/cacheflush.h>
#include <asm/exec.h>
#include <asm/fpsimd.h>
#include <asm/mmu_context.h>
#include <asm/mte.h>
#include <asm/processor.h>
#include <asm/pointer_auth.h>
#include <asm/stacktrace.h>

#if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
#include <linux/stackprotector.h>
unsigned long __stack_chk_guard __ro_after_init;
EXPORT_SYMBOL(__stack_chk_guard);
#endif

/*
 * Function pointers to optional machine specific functions
 */
void (*pm_power_off)(void);
EXPORT_SYMBOL_GPL(pm_power_off);

void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);

static void noinstr __cpu_do_idle(void)
{
    dsb(sy);
    wfi();
}

static void noinstr __cpu_do_idle_irqprio(void)
{
    unsigned long pmr;
    unsigned long daif_bits;

    daif_bits = read_sysreg(daif);
    write_sysreg(daif_bits | PSR_I_BIT, daif);

    /*
     * Unmask PMR before going idle to make sure interrupts can
     * be raised.
     */
    pmr = gic_read_pmr();
    gic_write_pmr(GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET);

    __cpu_do_idle();

    gic_write_pmr(pmr);
    write_sysreg(daif_bits, daif);
}

/*
 *    cpu_do_idle()
 *
 *    Idle the processor (wait for interrupt).
 *
 *    If the CPU supports priority masking we must do additional work to
 *    ensure that interrupts are not masked at the PMR (because the core will
 *    not wake up if we block the wake up signal in the interrupt controller).
 */
void noinstr cpu_do_idle(void)
{
    if (system_uses_irq_prio_masking()) {
        __cpu_do_idle_irqprio();
    } else {
        __cpu_do_idle();
    }
}

/*
 * This is our default idle handler.
 */
void noinstr arch_cpu_idle(void)
{
    /*
     * This should do all the clock switching and wait for interrupt
     * tricks
     */
    cpu_do_idle();
    raw_local_irq_enable();
}

#ifdef CONFIG_HOTPLUG_CPU
void arch_cpu_idle_dead(void)
{
    cpu_die();
}
#endif

/*
 * Called by kexec, immediately prior to machine_kexec().
 *
 * This must completely disable all secondary CPUs; simply causing those CPUs
 * to execute e.g. a RAM-based pin loop is not sufficient. This allows the
 * kexec'd kernel to use any and all RAM as it sees fit, without having to
 * avoid any code or data used by any SW CPU pin loop. The CPU hotplug
 * functionality embodied in smpt_shutdown_nonboot_cpus() to achieve this.
 */
void machine_shutdown(void)
{
    smp_shutdown_nonboot_cpus(reboot_cpu);
}

/*
 * Halting simply requires that the secondary CPUs stop performing any
 * activity (executing tasks, handling interrupts). smp_send_stop()
 * achieves this.
 */
void machine_halt(void)
{
    local_irq_disable();
    smp_send_stop();
    while (1) {
        ;
    }
}

/*
 * Power-off simply requires that the secondary CPUs stop performing any
 * activity (executing tasks, handling interrupts). smp_send_stop()
 * achieves this. When the system power is turned off, it will take all CPUs
 * with it.
 */
void machine_power_off(void)
{
    local_irq_disable();
    smp_send_stop();
    if (pm_power_off) {
        pm_power_off();
    }
}

/*
 * Restart requires that the secondary CPUs stop performing any activity
 * while the primary CPU resets the system. Systems with multiple CPUs must
 * provide a HW restart implementation, to ensure that all CPUs reset at once.
 * This is required so that any code running after reset on the primary CPU
 * doesn't have to co-ordinate with other CPUs to ensure they aren't still
 * executing pre-reset code, and using RAM that the primary CPU's code wishes
 * to use. Implementing such co-ordination would be essentially impossible.
 */
void machine_restart(char *cmd)
{
    /* Disable interrupts first */
    local_irq_disable();
    smp_send_stop();

    do_kernel_pre_restart(cmd);

    /*
     * UpdateCapsule() depends on the system being reset via
     * ResetSystem().
     */
    if (efi_enabled(EFI_RUNTIME_SERVICES)) {
        efi_reboot(reboot_mode, NULL);
    }

    /* Now call the architecture specific reboot code. */
    if (arm_pm_restart) {
        arm_pm_restart(reboot_mode, cmd);
    } else {
        do_kernel_restart(cmd);
    }

    /*
     * Whoops - the architecture was unable to reboot.
     */
    printk("Reboot failed -- System halted\n");
    while (1) {
        ;
    }
}

#define bstr(suffix, str) [PSR_BTYPE_##suffix >> PSR_BTYPE_SHIFT] = (str)
static const char *const btypes[] = {bstr(NONE, "--"), bstr(JC, "jc"), bstr(C, "-c"), bstr(J, "j-")};
#undef bstr

static void print_pstate(struct pt_regs *regs)
{
    u64 pstate = regs->pstate;

    if (compat_user_mode(regs)) {
        printk("pstate: %08llx (%c%c%c%c %c %s %s %c%c%c)\n", pstate, pstate & PSR_AA32_N_BIT ? 'N' : 'n',
               pstate & PSR_AA32_Z_BIT ? 'Z' : 'z', pstate & PSR_AA32_C_BIT ? 'C' : 'c',
               pstate & PSR_AA32_V_BIT ? 'V' : 'v', pstate & PSR_AA32_Q_BIT ? 'Q' : 'q',
               pstate & PSR_AA32_T_BIT ? "T32" : "A32", pstate & PSR_AA32_E_BIT ? "BE" : "LE",
               pstate & PSR_AA32_A_BIT ? 'A' : 'a', pstate & PSR_AA32_I_BIT ? 'I' : 'i',
               pstate & PSR_AA32_F_BIT ? 'F' : 'f');
    } else {
        const char *btype_str = btypes[(pstate & PSR_BTYPE_MASK) >> PSR_BTYPE_SHIFT];

        printk("pstate: %08llx (%c%c%c%c %c%c%c%c %cPAN %cUAO %cTCO BTYPE=%s)\n", pstate,
               pstate & PSR_N_BIT ? 'N' : 'n', pstate & PSR_Z_BIT ? 'Z' : 'z', pstate & PSR_C_BIT ? 'C' : 'c',
               pstate & PSR_V_BIT ? 'V' : 'v', pstate & PSR_D_BIT ? 'D' : 'd', pstate & PSR_A_BIT ? 'A' : 'a',
               pstate & PSR_I_BIT ? 'I' : 'i', pstate & PSR_F_BIT ? 'F' : 'f', pstate & PSR_PAN_BIT ? '+' : '-',
               pstate & PSR_UAO_BIT ? '+' : '-', pstate & PSR_TCO_BIT ? '+' : '-', btype_str);
    }
}

void __show_regs(struct pt_regs *regs)
{
    int i, top_reg;
    u64 lr, sp;

    if (compat_user_mode(regs)) {
        lr = regs->compat_lr;
        sp = regs->compat_sp;
        top_reg = 0x0c;
    } else {
        lr = regs->regs[0x1e];
        sp = regs->sp;
        top_reg = 0x1d;
    }

    show_regs_print_info(KERN_DEFAULT);
    print_pstate(regs);

    if (!user_mode(regs)) {
        printk("pc : %pS\n", (void *)regs->pc);
        printk("lr : %pS\n", (void *)ptrauth_strip_insn_pac(lr));
    } else {
        printk("pc : %016llx\n", regs->pc);
        printk("lr : %016llx\n", lr);
    }

    printk("sp : %016llx\n", sp);

    if (system_uses_irq_prio_masking()) {
        printk("pmr_save: %08llx\n", regs->pmr_save);
    }

    i = top_reg;

    while (i >= 0) {
        printk("x%-2d: %016llx ", i, regs->regs[i]);
        i--;

        if (i % 0x02 == 0) {
            pr_cont("x%-2d: %016llx ", i, regs->regs[i]);
            i--;
        }

        pr_cont("\n");
    }
}

void show_regs(struct pt_regs *regs)
{
    __show_regs(regs);
    dump_backtrace(regs, NULL, KERN_DEFAULT);
}

static void tls_thread_flush(void)
{
    write_sysreg(0, tpidr_el0);

    if (is_compat_task()) {
        current->thread.uw.tp_value = 0;

        /*
         * We need to ensure ordering between the shadow state and the
         * hardware state, so that we don't corrupt the hardware state
         * with a stale shadow state during context switch.
         */
        barrier();
        write_sysreg(0, tpidrro_el0);
    }
}

static void flush_tagged_addr_state(void)
{
    if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI)) {
        clear_thread_flag(TIF_TAGGED_ADDR);
    }
}

void flush_thread(void)
{
    fpsimd_flush_thread();
    tls_thread_flush();
    flush_ptrace_hw_breakpoint(current);
    flush_tagged_addr_state();
    flush_mte_state();
}

void release_thread(struct task_struct *dead_task)
{
}

void arch_release_task_struct(struct task_struct *tsk)
{
    fpsimd_release_task(tsk);
}

int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
{
    if (current->mm) {
        fpsimd_preserve_current_state();
    }
    *dst = *src;

    /* We rely on the above assignment to initialize dst's thread_flags: */
    BUILD_BUG_ON(!IS_ENABLED(CONFIG_THREAD_INFO_IN_TASK));

    /*
     * Detach src's sve_state (if any) from dst so that it does not
     * get erroneously used or freed prematurely.  dst's sve_state
     * will be allocated on demand later on if dst uses SVE.
     * For consistency, also clear TIF_SVE here: this could be done
     * later in copy_process(), but to avoid tripping up future
     * maintainers it is best not to leave TIF_SVE and sve_state in
     * an inconsistent state, even temporarily.
     */
    dst->thread.sve_state = NULL;
    clear_tsk_thread_flag(dst, TIF_SVE);

    /* clear any pending asynchronous tag fault raised by the parent */
    clear_tsk_thread_flag(dst, TIF_MTE_ASYNC_FAULT);

    return 0;
}

asmlinkage void ret_from_fork(void) asm("ret_from_fork");

int copy_thread(unsigned long clone_flags, unsigned long stack_start, unsigned long stk_sz, struct task_struct *p,
                unsigned long tls)
{
    struct pt_regs *childregs = task_pt_regs(p);

    memset(&p->thread.cpu_context, 0, sizeof(struct cpu_context));

    /*
     * In case p was allocated the same task_struct pointer as some
     * other recently-exited task, make sure p is disassociated from
     * any cpu that may have run that now-exited task recently.
     * Otherwise we could erroneously skip reloading the FPSIMD
     * registers for p.
     */
    fpsimd_flush_task_state(p);

    ptrauth_thread_init_kernel(p);

    if (likely(!(p->flags & PF_KTHREAD))) {
        *childregs = *current_pt_regs();
        childregs->regs[0] = 0;

        /*
         * Read the current TLS pointer from tpidr_el0 as it may be
         * out-of-sync with the saved value.
         */
        *task_user_tls(p) = read_sysreg(tpidr_el0);

        if (stack_start) {
            if (is_compat_thread(task_thread_info(p))) {
                childregs->compat_sp = stack_start;
            } else {
                childregs->sp = stack_start;
            }
        }

        /*
         * If a TLS pointer was passed to clone, use it for the new
         * thread.
         */
        if (clone_flags & CLONE_SETTLS) {
            p->thread.uw.tp_value = tls;
        }
    } else {
        memset(childregs, 0, sizeof(struct pt_regs));

        childregs->pstate = PSR_MODE_EL1h;
        if (IS_ENABLED(CONFIG_ARM64_UAO) && cpus_have_const_cap(ARM64_HAS_UAO)) {
            childregs->pstate |= PSR_UAO_BIT;
        }

        spectre_v4_enable_task_mitigation(p);

        if (system_uses_irq_prio_masking()) {
            childregs->pmr_save = GIC_PRIO_IRQON;
        }

        p->thread.cpu_context.x19 = stack_start;
        p->thread.cpu_context.x20 = stk_sz;
    }
    p->thread.cpu_context.pc = (unsigned long)ret_from_fork;
    p->thread.cpu_context.sp = (unsigned long)childregs;

    ptrace_hw_copy_thread(p);

    return 0;
}

void tls_preserve_current_state(void)
{
    *task_user_tls(current) = read_sysreg(tpidr_el0);
}

static void tls_thread_switch(struct task_struct *next)
{
    tls_preserve_current_state();

    if (is_compat_thread(task_thread_info(next))) {
        write_sysreg(next->thread.uw.tp_value, tpidrro_el0);
    } else if (!arm64_kernel_unmapped_at_el0()) {
        write_sysreg(0, tpidrro_el0);
    }

    write_sysreg(*task_user_tls(next), tpidr_el0);
}

/* Restore the UAO state depending on next's addr_limit */
void uao_thread_switch(struct task_struct *next)
{
    if (IS_ENABLED(CONFIG_ARM64_UAO)) {
        if (task_thread_info(next)->addr_limit == KERNEL_DS) {
            asm(ALTERNATIVE("nop", SET_PSTATE_UAO(1), ARM64_HAS_UAO));
        } else {
            asm(ALTERNATIVE("nop", SET_PSTATE_UAO(0), ARM64_HAS_UAO));
        }
    }
}

/*
 * Force SSBS state on context-switch, since it may be lost after migrating
 * from a CPU which treats the bit as RES0 in a heterogeneous system.
 */
static void ssbs_thread_switch(struct task_struct *next)
{
    /*
     * Nothing to do for kernel threads, but 'regs' may be junk
     * (e.g. idle task) so check the flags and bail early.
     */
    if (unlikely(next->flags & PF_KTHREAD)) {
        return;
    }

    /*
     * If all CPUs implement the SSBS extension, then we just need to
     * context-switch the PSTATE field.
     */
    if (cpus_have_const_cap(ARM64_SSBS)) {
        return;
    }

    spectre_v4_enable_task_mitigation(next);
}

/*
 * We store our current task in sp_el0, which is clobbered by userspace. Keep a
 * shadow copy so that we can restore this upon entry from userspace.
 *
 * This is *only* for exception entry from EL0, and is not valid until we
 * __switch_to() a user task.
 */
DEFINE_PER_CPU(struct task_struct *, __entry_task);

static void entry_task_switch(struct task_struct *next)
{
    __this_cpu_write(__entry_task, next);
}

/*
 * ARM erratum 1418040 handling, affecting the 32bit view of CNTVCT.
 * Assuming the virtual counter is enabled at the beginning of times:
 *
 * - disable access when switching from a 64bit task to a 32bit task
 * - enable access when switching from a 32bit task to a 64bit task
 */
static void erratum_1418040_thread_switch(struct task_struct *next)
{
    if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040) ||
        !this_cpu_has_cap(ARM64_WORKAROUND_1418040))
        return;

    if (is_compat_thread(task_thread_info(next)))
        sysreg_clear_set(cntkctl_el1, ARCH_TIMER_USR_VCT_ACCESS_EN, 0);
    else
        sysreg_clear_set(cntkctl_el1, 0, ARCH_TIMER_USR_VCT_ACCESS_EN);
    }

static void erratum_1418040_new_exec(void)
{
    preempt_disable();
    erratum_1418040_thread_switch(current);
    preempt_enable();
}

/*
 * Thread switching.
 */
__notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev, struct task_struct *next)
{
    struct task_struct *last;

    fpsimd_thread_switch(next);
    tls_thread_switch(next);
    hw_breakpoint_thread_switch(next);
    contextidr_thread_switch(next);
    entry_task_switch(next);
    uao_thread_switch(next);
    ssbs_thread_switch(next);
    erratum_1418040_thread_switch(next);

    /*
     * Complete any pending TLB or cache maintenance on this CPU in case
     * the thread migrates to a different CPU.
     * This full barrier is also required by the membarrier system
     * call.
     */
    dsb(ish);

    /*
     * MTE thread switching must happen after the DSB above to ensure that
     * any asynchronous tag check faults have been logged in the TFSR*_EL1
     * registers.
     */
    mte_thread_switch(next);

    /* the actual thread switch */
    last = cpu_switch_to(prev, next);

    return last;
}

unsigned long get_wchan(struct task_struct *p)
{
    struct stackframe frame;
    unsigned long stack_page, ret = 0;
    int count = 0;
    if (!p || p == current || p->state == TASK_RUNNING) {
        return 0;
    }

    stack_page = (unsigned long)try_get_task_stack(p);
    if (!stack_page) {
        return 0;
    }

    start_backtrace(&frame, thread_saved_fp(p), thread_saved_pc(p));

    do {
        if (unwind_frame(p, &frame)) {
            goto out;
        }
        if (!in_sched_functions(frame.pc)) {
            ret = frame.pc;
            goto out;
        }
    } while (count++ < 0x10);

out:
    put_task_stack(p);
    return ret;
}

unsigned long arch_align_stack(unsigned long sp)
{
    if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space) {
        sp -= get_random_int() & ~PAGE_MASK;
    }
    return sp & ~0xf;
}

/*
 * Called from setup_new_exec() after (COMPAT_)SET_PERSONALITY.
 */
void arch_setup_new_exec(void)
{
    current->mm->context.flags = is_compat_task() ? MMCF_AARCH32 : 0;

    ptrauth_thread_init_user(current);
    erratum_1418040_new_exec();

    if (task_spec_ssb_noexec(current)) {
        arch_prctl_spec_ctrl_set(current, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE);
    }
}

#ifdef CONFIG_ARM64_TAGGED_ADDR_ABI
/*
 * Control the relaxed ABI allowing tagged user addresses into the kernel.
 */
static unsigned int tagged_addr_disabled;

long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
{
    unsigned long valid_mask = PR_TAGGED_ADDR_ENABLE;
    struct thread_info *ti = task_thread_info(task);

    if (is_compat_thread(ti)) {
        return -EINVAL;
    }

    if (system_supports_mte()) {
        valid_mask |= PR_MTE_TCF_MASK | PR_MTE_TAG_MASK;
    }

    if (arg & ~valid_mask) {
        return -EINVAL;
    }

    /*
     * Do not allow the enabling of the tagged address ABI if globally
     * disabled via sysctl abi.tagged_addr_disabled.
     */
    if ((arg & PR_TAGGED_ADDR_ENABLE) && tagged_addr_disabled) {
        return -EINVAL;
    }

    if (set_mte_ctrl(task, arg) != 0) {
        return -EINVAL;
    }

    update_ti_thread_flag(ti, TIF_TAGGED_ADDR, arg & PR_TAGGED_ADDR_ENABLE);

    return 0;
}

long get_tagged_addr_ctrl(struct task_struct *task)
{
    long ret = 0;
    struct thread_info *ti = task_thread_info(task);

    if (is_compat_thread(ti)) {
        return -EINVAL;
    }

    if (test_ti_thread_flag(ti, TIF_TAGGED_ADDR)) {
        ret = PR_TAGGED_ADDR_ENABLE;
    }

    ret |= get_mte_ctrl(task);

    return ret;
}

/*
 * Global sysctl to disable the tagged user addresses support. This control
 * only prevents the tagged address ABI enabling via prctl() and does not
 * disable it for tasks that already opted in to the relaxed ABI.
 */

static struct ctl_table tagged_addr_sysctl_table[] = {
    {
        .procname = "tagged_addr_disabled",
        .mode = 0644,
        .data = &tagged_addr_disabled,
        .maxlen = sizeof(int),
        .proc_handler = proc_dointvec_minmax,
        .extra1 = SYSCTL_ZERO,
        .extra2 = SYSCTL_ONE,
    },
    {}
};

static int __init tagged_addr_init(void)
{
    if (!register_sysctl("abi", tagged_addr_sysctl_table)) {
        return -EINVAL;
    }
    return 0;
}

core_initcall(tagged_addr_init);
#endif /* CONFIG_ARM64_TAGGED_ADDR_ABI */

asmlinkage void __sched arm64_preempt_schedule_irq(void)
{
    lockdep_assert_irqs_disabled();

    /*
     * Preempting a task from an IRQ means we leave copies of PSTATE
     * on the stack. cpufeature's enable calls may modify PSTATE, but
     * resuming one of these preempted tasks would undo those changes.
     *
     * Only allow a task to be preempted once cpufeatures have been
     * enabled.
     */
    if (system_capabilities_finalized()) {
        preempt_schedule_irq();
    }
}

#ifdef CONFIG_BINFMT_ELF
int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state, bool has_interp, bool is_interp)
{
    /*
     * For dynamically linked executables the interpreter is
     * responsible for setting PROT_BTI on everything except
     * itself.
     */
    if (is_interp != has_interp) {
        return prot;
    }

    if (!(state->flags & ARM64_ELF_BTI)) {
        return prot;
    }

    if (prot & PROT_EXEC) {
        prot |= PROT_BTI;
    }

    return prot;
}
#endif