/*
 * ARMv8 single-step debug support and mdscr context switching.
 *
 * Copyright (C) 2012 ARM Limited
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Author: Will Deacon <will.deacon@arm.com>
 */

#include <linux/cpu.h>
#include <linux/debugfs.h>
#include <linux/hardirq.h>
#include <linux/init.h>
#include <linux/ptrace.h>
#include <linux/kprobes.h>
#include <linux/stat.h>
#include <linux/uaccess.h>
#include <linux/sched/task_stack.h>

#include <asm/cpufeature.h>
#include <asm/cputype.h>
#include <asm/daifflags.h>
#include <asm/debug-monitors.h>
#include <asm/system_misc.h>
#include <asm/traps.h>

/* Determine debug architecture. */
u8 debug_monitors_arch(void)
{
        return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1),
                                                ID_AA64DFR0_DEBUGVER_SHIFT);
}

/*
 * MDSCR access routines.
 */
static void mdscr_write(u32 mdscr)
{
        unsigned long flags;
        flags = local_daif_save();
        write_sysreg(mdscr, mdscr_el1);
        local_daif_restore(flags);
}
NOKPROBE_SYMBOL(mdscr_write);

static u32 mdscr_read(void)
{
        return read_sysreg(mdscr_el1);
}
NOKPROBE_SYMBOL(mdscr_read);

/*
 * Allow root to disable self-hosted debug from userspace.
 * This is useful if you want to connect an external JTAG debugger.
 */
static bool debug_enabled = true;

static int create_debug_debugfs_entry(void)
{
        debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
        return 0;
}
fs_initcall(create_debug_debugfs_entry);

static int __init early_debug_disable(char *buf)
{
        debug_enabled = false;
        return 0;
}

early_param("nodebugmon", early_debug_disable);

/*
 * Keep track of debug users on each core.
 * The ref counts are per-cpu so we use a local_t type.
 */
static DEFINE_PER_CPU(int, mde_ref_count);
static DEFINE_PER_CPU(int, kde_ref_count);

void enable_debug_monitors(enum dbg_active_el el)
{
        u32 mdscr, enable = 0;

        WARN_ON(preemptible());

        if (this_cpu_inc_return(mde_ref_count) == 1)
                enable = DBG_MDSCR_MDE;

        if (el == DBG_ACTIVE_EL1 &&
            this_cpu_inc_return(kde_ref_count) == 1)
                enable |= DBG_MDSCR_KDE;

        if (enable && debug_enabled) {
                mdscr = mdscr_read();
                mdscr |= enable;
                mdscr_write(mdscr);
        }
}
NOKPROBE_SYMBOL(enable_debug_monitors);

void disable_debug_monitors(enum dbg_active_el el)
{
        u32 mdscr, disable = 0;

        WARN_ON(preemptible());

        if (this_cpu_dec_return(mde_ref_count) == 0)
                disable = ~DBG_MDSCR_MDE;

        if (el == DBG_ACTIVE_EL1 &&
            this_cpu_dec_return(kde_ref_count) == 0)
                disable &= ~DBG_MDSCR_KDE;

        if (disable) {
                mdscr = mdscr_read();
                mdscr &= disable;
                mdscr_write(mdscr);
        }
}
NOKPROBE_SYMBOL(disable_debug_monitors);

/*
 * OS lock clearing.
 */
static int clear_os_lock(unsigned int cpu)
{
        write_sysreg(0, oslar_el1);
        isb();
        return 0;
}

static int debug_monitors_init(void)
{
        return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
                                 "arm64/debug_monitors:starting",
                                 clear_os_lock, NULL);
}
postcore_initcall(debug_monitors_init);

/*
 * Single step API and exception handling.
 */
static void set_regs_spsr_ss(struct pt_regs *regs)
{
        regs->pstate |= DBG_SPSR_SS;
}
NOKPROBE_SYMBOL(set_regs_spsr_ss);

static void clear_regs_spsr_ss(struct pt_regs *regs)
{
        regs->pstate &= ~DBG_SPSR_SS;
}
NOKPROBE_SYMBOL(clear_regs_spsr_ss);

/* EL1 Single Step Handler hooks */
static LIST_HEAD(step_hook);
static DEFINE_SPINLOCK(step_hook_lock);

void register_step_hook(struct step_hook *hook)
{
        spin_lock(&step_hook_lock);
        list_add_rcu(&hook->node, &step_hook);
        spin_unlock(&step_hook_lock);
}

void unregister_step_hook(struct step_hook *hook)
{
        spin_lock(&step_hook_lock);
        list_del_rcu(&hook->node);
        spin_unlock(&step_hook_lock);
        synchronize_rcu();
}

/*
 * Call registered single step handlers
 * There is no Syndrome info to check for determining the handler.
 * So we call all the registered handlers, until the right handler is
 * found which returns zero.
 */
static int call_step_hook(struct pt_regs *regs, unsigned int esr)
{
        struct step_hook *hook;
        int retval = DBG_HOOK_ERROR;

        rcu_read_lock();

        list_for_each_entry_rcu(hook, &step_hook, node) {
                retval = hook->fn(regs, esr);
                if (retval == DBG_HOOK_HANDLED)
                        break;
        }

        rcu_read_unlock();

        return retval;
}
NOKPROBE_SYMBOL(call_step_hook);

static void send_user_sigtrap(int si_code)
{
        struct pt_regs *regs = current_pt_regs();

        if (WARN_ON(!user_mode(regs)))
                return;

        if (interrupts_enabled(regs))
                local_irq_enable();

        arm64_force_sig_fault(SIGTRAP, si_code,
                             (void __user *)instruction_pointer(regs),
                             "User debug trap");
}

static int single_step_handler(unsigned long addr, unsigned int esr,
                               struct pt_regs *regs)
{
        bool handler_found = false;

        /*
         * If we are stepping a pending breakpoint, call the hw_breakpoint
         * handler first.
         */
        if (!reinstall_suspended_bps(regs))
                return 0;

#ifdef  CONFIG_KPROBES
        if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
                handler_found = true;
#endif
        if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
                handler_found = true;

        if (!handler_found && user_mode(regs)) {
                send_user_sigtrap(TRAP_TRACE);

                /*
                 * ptrace will disable single step unless explicitly
                 * asked to re-enable it. For other clients, it makes
                 * sense to leave it enabled (i.e. rewind the controls
                 * to the active-not-pending state).
                 */
                user_rewind_single_step(current);
        } else if (!handler_found) {
                pr_warn("Unexpected kernel single-step exception at EL1\n");
                /*
                 * Re-enable stepping since we know that we will be
                 * returning to regs.
                 */
                set_regs_spsr_ss(regs);
        }

        return 0;
}
NOKPROBE_SYMBOL(single_step_handler);

/*
 * Breakpoint handler is re-entrant as another breakpoint can
 * hit within breakpoint handler, especically in kprobes.
 * Use reader/writer locks instead of plain spinlock.
 */
static LIST_HEAD(break_hook);
static DEFINE_SPINLOCK(break_hook_lock);

void register_break_hook(struct break_hook *hook)
{
        spin_lock(&break_hook_lock);
        list_add_rcu(&hook->node, &break_hook);
        spin_unlock(&break_hook_lock);
}

void unregister_break_hook(struct break_hook *hook)
{
        spin_lock(&break_hook_lock);
        list_del_rcu(&hook->node);
        spin_unlock(&break_hook_lock);
        synchronize_rcu();
}

static int call_break_hook(struct pt_regs *regs, unsigned int esr)
{
        struct break_hook *hook;
        int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;

        rcu_read_lock();
        list_for_each_entry_rcu(hook, &break_hook, node)
                if ((esr & hook->esr_mask) == hook->esr_val)
                        fn = hook->fn;
        rcu_read_unlock();

        return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
}
NOKPROBE_SYMBOL(call_break_hook);

static int brk_handler(unsigned long addr, unsigned int esr,
                       struct pt_regs *regs)
{
        bool handler_found = false;

#ifdef  CONFIG_KPROBES
        if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
                if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED)
                        handler_found = true;
        }
#endif
        if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
                handler_found = true;

        if (!handler_found && user_mode(regs)) {
                send_user_sigtrap(TRAP_BRKPT);
        } else if (!handler_found) {
                pr_warn("Unexpected kernel BRK exception at EL1\n");
                return -EFAULT;
        }

        return 0;
}
NOKPROBE_SYMBOL(brk_handler);

int aarch32_break_handler(struct pt_regs *regs)
{
        u32 arm_instr;
        u16 thumb_instr;
        bool bp = false;
        void __user *pc = (void __user *)instruction_pointer(regs);

        if (!compat_user_mode(regs))
                return -EFAULT;

        if (compat_thumb_mode(regs)) {
                /* get 16-bit Thumb instruction */
                __le16 instr;
                get_user(instr, (__le16 __user *)pc);
                thumb_instr = le16_to_cpu(instr);
                if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
                        /* get second half of 32-bit Thumb-2 instruction */
                        get_user(instr, (__le16 __user *)(pc + 2));
                        thumb_instr = le16_to_cpu(instr);
                        bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
                } else {
                        bp = thumb_instr == AARCH32_BREAK_THUMB;
                }
        } else {
                /* 32-bit ARM instruction */
                __le32 instr;
                get_user(instr, (__le32 __user *)pc);
                arm_instr = le32_to_cpu(instr);
                bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
        }

        if (!bp)
                return -EFAULT;

        send_user_sigtrap(TRAP_BRKPT);
        return 0;
}
NOKPROBE_SYMBOL(aarch32_break_handler);

static int __init debug_traps_init(void)
{
        hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
                              TRAP_TRACE, "single-step handler");
        hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
                              TRAP_BRKPT, "ptrace BRK handler");
        return 0;
}
arch_initcall(debug_traps_init);

/* Re-enable single step for syscall restarting. */
void user_rewind_single_step(struct task_struct *task)
{
        /*
         * If single step is active for this thread, then set SPSR.SS
         * to 1 to avoid returning to the active-pending state.
         */
        if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
                set_regs_spsr_ss(task_pt_regs(task));
}
NOKPROBE_SYMBOL(user_rewind_single_step);

void user_fastforward_single_step(struct task_struct *task)
{
        if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
                clear_regs_spsr_ss(task_pt_regs(task));
}

/* Kernel API */
void kernel_enable_single_step(struct pt_regs *regs)
{
        WARN_ON(!irqs_disabled());
        set_regs_spsr_ss(regs);
        mdscr_write(mdscr_read() | DBG_MDSCR_SS);
        enable_debug_monitors(DBG_ACTIVE_EL1);
}
NOKPROBE_SYMBOL(kernel_enable_single_step);

void kernel_disable_single_step(void)
{
        WARN_ON(!irqs_disabled());
        mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
        disable_debug_monitors(DBG_ACTIVE_EL1);
}
NOKPROBE_SYMBOL(kernel_disable_single_step);

int kernel_active_single_step(void)
{
        WARN_ON(!irqs_disabled());
        return mdscr_read() & DBG_MDSCR_SS;
}
NOKPROBE_SYMBOL(kernel_active_single_step);

/* ptrace API */
void user_enable_single_step(struct task_struct *task)
{
        struct thread_info *ti = task_thread_info(task);

        if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
                set_regs_spsr_ss(task_pt_regs(task));
}
NOKPROBE_SYMBOL(user_enable_single_step);

void user_disable_single_step(struct task_struct *task)
{
        clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
}
NOKPROBE_SYMBOL(user_disable_single_step);