// SPDX-License-Identifier: GPL-2.0
#define pr_fmt(fmt) "kcov: " fmt

#define DISABLE_BRANCH_PROFILING
#include <linux/atomic.h>
#include <linux/compiler.h>
#include <linux/errno.h>
#include <linux/export.h>
#include <linux/types.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/preempt.h>
#include <linux/printk.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/kcov.h>
#include <asm/setup.h>

/* Number of 64-bit words written per one comparison: */
#define KCOV_WORDS_PER_CMP 4

/*
 * kcov descriptor (one per opened debugfs file).
 * State transitions of the descriptor:
 *  - initial state after open()
 *  - then there must be a single ioctl(KCOV_INIT_TRACE) call
 *  - then, mmap() call (several calls are allowed but not useful)
 *  - then, ioctl(KCOV_ENABLE, arg), where arg is
 *      KCOV_TRACE_PC - to trace only the PCs
 *      or
 *      KCOV_TRACE_CMP - to trace only the comparison operands
 *  - then, ioctl(KCOV_DISABLE) to disable the task.
 * Enabling/disabling ioctls can be repeated (only one task a time allowed).
 */
struct kcov {
        /*
         * Reference counter. We keep one for:
         *  - opened file descriptor
         *  - task with enabled coverage (we can't unwire it from another task)
         */
        atomic_t                refcount;
        /* The lock protects mode, size, area and t. */
        spinlock_t              lock;
        enum kcov_mode          mode;
        /* Size of arena (in long's for KCOV_MODE_TRACE). */
        unsigned                size;
        /* Coverage buffer shared with user space. */
        void                    *area;
        /* Task for which we collect coverage, or NULL. */
        struct task_struct      *t;
};

static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
{
        unsigned int mode;

        /*
         * We are interested in code coverage as a function of a syscall inputs,
         * so we ignore code executed in interrupts.
         */
        if (!in_task())
                return false;
        mode = READ_ONCE(t->kcov_mode);
        /*
         * There is some code that runs in interrupts but for which
         * in_interrupt() returns false (e.g. preempt_schedule_irq()).
         * READ_ONCE()/barrier() effectively provides load-acquire wrt
         * interrupts, there are paired barrier()/WRITE_ONCE() in
         * kcov_ioctl_locked().
         */
        barrier();
        return mode == needed_mode;
}

static notrace unsigned long canonicalize_ip(unsigned long ip)
{
#ifdef CONFIG_RANDOMIZE_BASE
        ip -= kaslr_offset();
#endif
        return ip;
}

/*
 * Entry point from instrumented code.
 * This is called once per basic-block/edge.
 */
void notrace __sanitizer_cov_trace_pc(void)
{
        struct task_struct *t;
        unsigned long *area;
        unsigned long ip = canonicalize_ip(_RET_IP_);
        unsigned long pos;

        t = current;
        if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
                return;

        area = t->kcov_area;
        /* The first 64-bit word is the number of subsequent PCs. */
        pos = READ_ONCE(area[0]) + 1;
        if (likely(pos < t->kcov_size)) {
                area[pos] = ip;
                WRITE_ONCE(area[0], pos);
        }
}
EXPORT_SYMBOL(__sanitizer_cov_trace_pc);

#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
static void write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
{
        struct task_struct *t;
        u64 *area;
        u64 count, start_index, end_pos, max_pos;

        t = current;
        if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
                return;

        ip = canonicalize_ip(ip);

        /*
         * We write all comparison arguments and types as u64.
         * The buffer was allocated for t->kcov_size unsigned longs.
         */
        area = (u64 *)t->kcov_area;
        max_pos = t->kcov_size * sizeof(unsigned long);

        count = READ_ONCE(area[0]);

        /* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
        start_index = 1 + count * KCOV_WORDS_PER_CMP;
        end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
        if (likely(end_pos <= max_pos)) {
                area[start_index] = type;
                area[start_index + 1] = arg1;
                area[start_index + 2] = arg2;
                area[start_index + 3] = ip;
                WRITE_ONCE(area[0], count + 1);
        }
}

void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
{
        write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);

void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
{
        write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);

void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
{
        write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);

void notrace __sanitizer_cov_trace_cmp8(u64 arg1, u64 arg2)
{
        write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);

void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
{
        write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
                        _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);

void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
{
        write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
                        _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);

void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)
{
        write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
                        _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);

void notrace __sanitizer_cov_trace_const_cmp8(u64 arg1, u64 arg2)
{
        write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
                        _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);

void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
{
        u64 i;
        u64 count = cases[0];
        u64 size = cases[1];
        u64 type = KCOV_CMP_CONST;

        switch (size) {
        case 8:
                type |= KCOV_CMP_SIZE(0);
                break;
        case 16:
                type |= KCOV_CMP_SIZE(1);
                break;
        case 32:
                type |= KCOV_CMP_SIZE(2);
                break;
        case 64:
                type |= KCOV_CMP_SIZE(3);
                break;
        default:
                return;
        }
        for (i = 0; i < count; i++)
                write_comp_data(type, cases[i + 2], val, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
#endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */

static void kcov_get(struct kcov *kcov)
{
        atomic_inc(&kcov->refcount);
}

static void kcov_put(struct kcov *kcov)
{
        if (atomic_dec_and_test(&kcov->refcount)) {
                vfree(kcov->area);
                kfree(kcov);
        }
}

void kcov_task_init(struct task_struct *t)
{
        WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
        barrier();
        t->kcov_size = 0;
        t->kcov_area = NULL;
        t->kcov = NULL;
}

void kcov_task_exit(struct task_struct *t)
{
        struct kcov *kcov;

        kcov = t->kcov;
        if (kcov == NULL)
                return;
        spin_lock(&kcov->lock);
        if (WARN_ON(kcov->t != t)) {
                spin_unlock(&kcov->lock);
                return;
        }
        /* Just to not leave dangling references behind. */
        kcov_task_init(t);
        kcov->t = NULL;
        kcov->mode = KCOV_MODE_INIT;
        spin_unlock(&kcov->lock);
        kcov_put(kcov);
}

static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
{
        int res = 0;
        void *area;
        struct kcov *kcov = vma->vm_file->private_data;
        unsigned long size, off;
        struct page *page;

        area = vmalloc_user(vma->vm_end - vma->vm_start);
        if (!area)
                return -ENOMEM;

        spin_lock(&kcov->lock);
        size = kcov->size * sizeof(unsigned long);
        if (kcov->mode != KCOV_MODE_INIT || vma->vm_pgoff != 0 ||
            vma->vm_end - vma->vm_start != size) {
                res = -EINVAL;
                goto exit;
        }
        if (!kcov->area) {
                kcov->area = area;
                vma->vm_flags |= VM_DONTEXPAND;
                spin_unlock(&kcov->lock);
                for (off = 0; off < size; off += PAGE_SIZE) {
                        page = vmalloc_to_page(kcov->area + off);
                        if (vm_insert_page(vma, vma->vm_start + off, page))
                                WARN_ONCE(1, "vm_insert_page() failed");
                }
                return 0;
        }
exit:
        spin_unlock(&kcov->lock);
        vfree(area);
        return res;
}

static int kcov_open(struct inode *inode, struct file *filep)
{
        struct kcov *kcov;

        kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
        if (!kcov)
                return -ENOMEM;
        kcov->mode = KCOV_MODE_DISABLED;
        atomic_set(&kcov->refcount, 1);
        spin_lock_init(&kcov->lock);
        filep->private_data = kcov;
        return nonseekable_open(inode, filep);
}

static int kcov_close(struct inode *inode, struct file *filep)
{
        kcov_put(filep->private_data);
        return 0;
}

/*
 * Fault in a lazily-faulted vmalloc area before it can be used by
 * __santizer_cov_trace_pc(), to avoid recursion issues if any code on the
 * vmalloc fault handling path is instrumented.
 */
static void kcov_fault_in_area(struct kcov *kcov)
{
        unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
        unsigned long *area = kcov->area;
        unsigned long offset;

        for (offset = 0; offset < kcov->size; offset += stride)
                READ_ONCE(area[offset]);
}

static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
                             unsigned long arg)
{
        struct task_struct *t;
        unsigned long size, unused;

        switch (cmd) {
        case KCOV_INIT_TRACE:
                /*
                 * Enable kcov in trace mode and setup buffer size.
                 * Must happen before anything else.
                 */
                if (kcov->mode != KCOV_MODE_DISABLED)
                        return -EBUSY;
                /*
                 * Size must be at least 2 to hold current position and one PC.
                 * Later we allocate size * sizeof(unsigned long) memory,
                 * that must not overflow.
                 */
                size = arg;
                if (size < 2 || size > INT_MAX / sizeof(unsigned long))
                        return -EINVAL;
                kcov->size = size;
                kcov->mode = KCOV_MODE_INIT;
                return 0;
        case KCOV_ENABLE:
                /*
                 * Enable coverage for the current task.
                 * At this point user must have been enabled trace mode,
                 * and mmapped the file. Coverage collection is disabled only
                 * at task exit or voluntary by KCOV_DISABLE. After that it can
                 * be enabled for another task.
                 */
                if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
                        return -EINVAL;
                t = current;
                if (kcov->t != NULL || t->kcov != NULL)
                        return -EBUSY;
                if (arg == KCOV_TRACE_PC)
                        kcov->mode = KCOV_MODE_TRACE_PC;
                else if (arg == KCOV_TRACE_CMP)
#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
                        kcov->mode = KCOV_MODE_TRACE_CMP;
#else
                return -ENOTSUPP;
#endif
                else
                        return -EINVAL;
                kcov_fault_in_area(kcov);
                /* Cache in task struct for performance. */
                t->kcov_size = kcov->size;
                t->kcov_area = kcov->area;
                /* See comment in check_kcov_mode(). */
                barrier();
                WRITE_ONCE(t->kcov_mode, kcov->mode);
                t->kcov = kcov;
                kcov->t = t;
                /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
                kcov_get(kcov);
                return 0;
        case KCOV_DISABLE:
                /* Disable coverage for the current task. */
                unused = arg;
                if (unused != 0 || current->kcov != kcov)
                        return -EINVAL;
                t = current;
                if (WARN_ON(kcov->t != t))
                        return -EINVAL;
                kcov_task_init(t);
                kcov->t = NULL;
                kcov->mode = KCOV_MODE_INIT;
                kcov_put(kcov);
                return 0;
        default:
                return -ENOTTY;
        }
}

static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
{
        struct kcov *kcov;
        int res;

        kcov = filep->private_data;
        spin_lock(&kcov->lock);
        res = kcov_ioctl_locked(kcov, cmd, arg);
        spin_unlock(&kcov->lock);
        return res;
}

static const struct file_operations kcov_fops = {
        .open           = kcov_open,
        .unlocked_ioctl = kcov_ioctl,
        .compat_ioctl   = kcov_ioctl,
        .mmap           = kcov_mmap,
        .release        = kcov_close,
};

static int __init kcov_init(void)
{
        /*
         * The kcov debugfs file won't ever get removed and thus,
         * there is no need to protect it against removal races. The
         * use of debugfs_create_file_unsafe() is actually safe here.
         */
        if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
                pr_err("failed to create kcov in debugfs\n");
                return -ENOMEM;
        }
        return 0;
}

device_initcall(kcov_init);