// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2017 Arm Ltd.
#define pr_fmt(fmt) "sdei: " fmt

#include <linux/arm_sdei.h>
#include <linux/hardirq.h>
#include <linux/irqflags.h>
#include <linux/sched/task_stack.h>
#include <linux/uaccess.h>

#include <asm/alternative.h>
#include <asm/kprobes.h>
#include <asm/mmu.h>
#include <asm/ptrace.h>
#include <asm/sections.h>
#include <asm/stacktrace.h>
#include <asm/sysreg.h>
#include <asm/vmap_stack.h>

unsigned long sdei_exit_mode;

/*
 * VMAP'd stacks checking for stack overflow on exception using sp as a scratch
 * register, meaning SDEI has to switch to its own stack. We need two stacks as
 * a critical event may interrupt a normal event that has just taken a
 * synchronous exception, and is using sp as scratch register. For a critical
 * event interrupting a normal event, we can't reliably tell if we were on the
 * sdei stack.
 * For now, we allocate stacks when the driver is probed.
 */
DECLARE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
DECLARE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);

#ifdef CONFIG_VMAP_STACK
DEFINE_PER_CPU(unsigned long *, sdei_stack_normal_ptr);
DEFINE_PER_CPU(unsigned long *, sdei_stack_critical_ptr);
#endif

static void _free_sdei_stack(unsigned long * __percpu *ptr, int cpu)
{
        unsigned long *p;

        p = per_cpu(*ptr, cpu);
        if (p) {
                per_cpu(*ptr, cpu) = NULL;
                vfree(p);
        }
}

static void free_sdei_stacks(void)
{
        int cpu;

        for_each_possible_cpu(cpu) {
                _free_sdei_stack(&sdei_stack_normal_ptr, cpu);
                _free_sdei_stack(&sdei_stack_critical_ptr, cpu);
        }
}

static int _init_sdei_stack(unsigned long * __percpu *ptr, int cpu)
{
        unsigned long *p;

        p = arch_alloc_vmap_stack(SDEI_STACK_SIZE, cpu_to_node(cpu));
        if (!p)
                return -ENOMEM;
        per_cpu(*ptr, cpu) = p;

        return 0;
}

static int init_sdei_stacks(void)
{
        int cpu;
        int err = 0;

        for_each_possible_cpu(cpu) {
                err = _init_sdei_stack(&sdei_stack_normal_ptr, cpu);
                if (err)
                        break;
                err = _init_sdei_stack(&sdei_stack_critical_ptr, cpu);
                if (err)
                        break;
        }

        if (err)
                free_sdei_stacks();

        return err;
}

static bool on_sdei_normal_stack(unsigned long sp, struct stack_info *info)
{
        unsigned long low = (unsigned long)raw_cpu_read(sdei_stack_normal_ptr);
        unsigned long high = low + SDEI_STACK_SIZE;

        if (!low)
                return false;

        if (sp < low || sp >= high)
                return false;

        if (info) {
                info->low = low;
                info->high = high;
                info->type = STACK_TYPE_SDEI_NORMAL;
        }

        return true;
}

static bool on_sdei_critical_stack(unsigned long sp, struct stack_info *info)
{
        unsigned long low = (unsigned long)raw_cpu_read(sdei_stack_critical_ptr);
        unsigned long high = low + SDEI_STACK_SIZE;

        if (!low)
                return false;

        if (sp < low || sp >= high)
                return false;

        if (info) {
                info->low = low;
                info->high = high;
                info->type = STACK_TYPE_SDEI_CRITICAL;
        }

        return true;
}

bool _on_sdei_stack(unsigned long sp, struct stack_info *info)
{
        if (!IS_ENABLED(CONFIG_VMAP_STACK))
                return false;

        if (on_sdei_critical_stack(sp, info))
                return true;

        if (on_sdei_normal_stack(sp, info))
                return true;

        return false;
}

unsigned long sdei_arch_get_entry_point(int conduit)
{
        /*
         * SDEI works between adjacent exception levels. If we booted at EL1 we
         * assume a hypervisor is marshalling events. If we booted at EL2 and
         * dropped to EL1 because we don't support VHE, then we can't support
         * SDEI.
         */
        if (is_hyp_mode_available() && !is_kernel_in_hyp_mode()) {
                pr_err("Not supported on this hardware/boot configuration\n");
                return 0;
        }

        if (IS_ENABLED(CONFIG_VMAP_STACK)) {
                if (init_sdei_stacks())
                        return 0;
        }

        sdei_exit_mode = (conduit == CONDUIT_HVC) ? SDEI_EXIT_HVC : SDEI_EXIT_SMC;

#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
        if (arm64_kernel_unmapped_at_el0()) {
                unsigned long offset;

                offset = (unsigned long)__sdei_asm_entry_trampoline -
                         (unsigned long)__entry_tramp_text_start;
                return TRAMP_VALIAS + offset;
        } else
#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
                return (unsigned long)__sdei_asm_handler;

}

/*
 * __sdei_handler() returns one of:
 *  SDEI_EV_HANDLED -  success, return to the interrupted context.
 *  SDEI_EV_FAILED  -  failure, return this error code to firmare.
 *  virtual-address -  success, return to this address.
 */
static __kprobes unsigned long _sdei_handler(struct pt_regs *regs,
                                             struct sdei_registered_event *arg)
{
        u32 mode;
        int i, err = 0;
        int clobbered_registers = 4;
        u64 elr = read_sysreg(elr_el1);
        u32 kernel_mode = read_sysreg(CurrentEL) | 1;   /* +SPSel */
        unsigned long vbar = read_sysreg(vbar_el1);

        if (arm64_kernel_unmapped_at_el0())
                clobbered_registers++;

        /* Retrieve the missing registers values */
        for (i = 0; i < clobbered_registers; i++) {
                /* from within the handler, this call always succeeds */
                sdei_api_event_context(i, &regs->regs[i]);
        }

        /*
         * We didn't take an exception to get here, set PAN. UAO will be cleared
         * by sdei_event_handler()s set_fs(USER_DS) call.
         */
        __uaccess_enable_hw_pan();

        err = sdei_event_handler(regs, arg);
        if (err)
                return SDEI_EV_FAILED;

        if (elr != read_sysreg(elr_el1)) {
                /*
                 * We took a synchronous exception from the SDEI handler.
                 * This could deadlock, and if you interrupt KVM it will
                 * hyp-panic instead.
                 */
                pr_warn("unsafe: exception during handler\n");
        }

        mode = regs->pstate & (PSR_MODE32_BIT | PSR_MODE_MASK);

        /*
         * If we interrupted the kernel with interrupts masked, we always go
         * back to wherever we came from.
         */
        if (mode == kernel_mode && !interrupts_enabled(regs))
                return SDEI_EV_HANDLED;

        /*
         * Otherwise, we pretend this was an IRQ. This lets user space tasks
         * receive signals before we return to them, and KVM to invoke it's
         * world switch to do the same.
         *
         * See DDI0487B.a Table D1-7 'Vector offsets from vector table base
         * address'.
         */
        if (mode == kernel_mode)
                return vbar + 0x280;
        else if (mode & PSR_MODE32_BIT)
                return vbar + 0x680;

        return vbar + 0x480;
}


asmlinkage __kprobes notrace unsigned long
__sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg)
{
        unsigned long ret;
        bool do_nmi_exit = false;

        /*
         * nmi_enter() deals with printk() re-entrance and use of RCU when
         * RCU believed this CPU was idle. Because critical events can
         * interrupt normal events, we may already be in_nmi().
         */
        if (!in_nmi()) {
                nmi_enter();
                do_nmi_exit = true;
        }

        ret = _sdei_handler(regs, arg);

        if (do_nmi_exit)
                nmi_exit();

        return ret;
}