// SPDX-License-Identifier: GPL-2.0

#include <linux/atomic.h>
#include <linux/bsearch.h>
#include <linux/bug.h>
#include <linux/debugfs.h>
#include <linux/init.h>
#include <linux/kallsyms.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/sort.h>
#include <linux/string.h>
#include <linux/uaccess.h>

#include "kcsan.h"

/*
 * Statistics counters.
 */
static atomic_long_t counters[KCSAN_COUNTER_COUNT];

/*
 * Addresses for filtering functions from reporting. This list can be used as a
 * whitelist or blacklist.
 */
static struct {
        unsigned long   *addrs;         /* array of addresses */
        size_t          size;           /* current size */
        int             used;           /* number of elements used */
        bool            sorted;         /* if elements are sorted */
        bool            whitelist;      /* if list is a blacklist or whitelist */
} report_filterlist = {
        .addrs          = NULL,
        .size           = 8,            /* small initial size */
        .used           = 0,
        .sorted         = false,
        .whitelist      = false,        /* default is blacklist */
};
static DEFINE_SPINLOCK(report_filterlist_lock);

static const char *counter_to_name(enum kcsan_counter_id id)
{
        switch (id) {
        case KCSAN_COUNTER_USED_WATCHPOINTS:            return "used_watchpoints";
        case KCSAN_COUNTER_SETUP_WATCHPOINTS:           return "setup_watchpoints";
        case KCSAN_COUNTER_DATA_RACES:                  return "data_races";
        case KCSAN_COUNTER_ASSERT_FAILURES:             return "assert_failures";
        case KCSAN_COUNTER_NO_CAPACITY:                 return "no_capacity";
        case KCSAN_COUNTER_REPORT_RACES:                return "report_races";
        case KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN:        return "races_unknown_origin";
        case KCSAN_COUNTER_UNENCODABLE_ACCESSES:        return "unencodable_accesses";
        case KCSAN_COUNTER_ENCODING_FALSE_POSITIVES:    return "encoding_false_positives";
        case KCSAN_COUNTER_COUNT:
                BUG();
        }
        return NULL;
}

void kcsan_counter_inc(enum kcsan_counter_id id)
{
        atomic_long_inc(&counters[id]);
}

void kcsan_counter_dec(enum kcsan_counter_id id)
{
        atomic_long_dec(&counters[id]);
}

/*
 * The microbenchmark allows benchmarking KCSAN core runtime only. To run
 * multiple threads, pipe 'microbench=<iters>' from multiple tasks into the
 * debugfs file. This will not generate any conflicts, and tests fast-path only.
 */
static noinline void microbenchmark(unsigned long iters)
{
        const struct kcsan_ctx ctx_save = current->kcsan_ctx;
        const bool was_enabled = READ_ONCE(kcsan_enabled);
        cycles_t cycles;

        /* We may have been called from an atomic region; reset context. */
        memset(&current->kcsan_ctx, 0, sizeof(current->kcsan_ctx));
        /*
         * Disable to benchmark fast-path for all accesses, and (expected
         * negligible) call into slow-path, but never set up watchpoints.
         */
        WRITE_ONCE(kcsan_enabled, false);

        pr_info("KCSAN: %s begin | iters: %lu\n", __func__, iters);

        cycles = get_cycles();
        while (iters--) {
                unsigned long addr = iters & ((PAGE_SIZE << 8) - 1);
                int type = !(iters & 0x7f) ? KCSAN_ACCESS_ATOMIC :
                                (!(iters & 0xf) ? KCSAN_ACCESS_WRITE : 0);
                __kcsan_check_access((void *)addr, sizeof(long), type);
        }
        cycles = get_cycles() - cycles;

        pr_info("KCSAN: %s end   | cycles: %llu\n", __func__, cycles);

        WRITE_ONCE(kcsan_enabled, was_enabled);
        /* restore context */
        current->kcsan_ctx = ctx_save;
}

/*
 * Simple test to create conflicting accesses. Write 'test=<iters>' to KCSAN's
 * debugfs file from multiple tasks to generate real conflicts and show reports.
 */
static long test_dummy;
static long test_flags;
static long test_scoped;
static noinline void test_thread(unsigned long iters)
{
        const long CHANGE_BITS = 0xff00ff00ff00ff00L;
        const struct kcsan_ctx ctx_save = current->kcsan_ctx;
        cycles_t cycles;

        /* We may have been called from an atomic region; reset context. */
        memset(&current->kcsan_ctx, 0, sizeof(current->kcsan_ctx));

        pr_info("KCSAN: %s begin | iters: %lu\n", __func__, iters);
        pr_info("test_dummy@%px, test_flags@%px, test_scoped@%px,\n",
                &test_dummy, &test_flags, &test_scoped);

        cycles = get_cycles();
        while (iters--) {
                /* These all should generate reports. */
                __kcsan_check_read(&test_dummy, sizeof(test_dummy));
                ASSERT_EXCLUSIVE_WRITER(test_dummy);
                ASSERT_EXCLUSIVE_ACCESS(test_dummy);

                ASSERT_EXCLUSIVE_BITS(test_flags, ~CHANGE_BITS); /* no report */
                __kcsan_check_read(&test_flags, sizeof(test_flags)); /* no report */

                ASSERT_EXCLUSIVE_BITS(test_flags, CHANGE_BITS); /* report */
                __kcsan_check_read(&test_flags, sizeof(test_flags)); /* no report */

                /* not actually instrumented */
                WRITE_ONCE(test_dummy, iters);  /* to observe value-change */
                __kcsan_check_write(&test_dummy, sizeof(test_dummy));

                test_flags ^= CHANGE_BITS; /* generate value-change */
                __kcsan_check_write(&test_flags, sizeof(test_flags));

                BUG_ON(current->kcsan_ctx.scoped_accesses.prev);
                {
                        /* Should generate reports anywhere in this block. */
                        ASSERT_EXCLUSIVE_WRITER_SCOPED(test_scoped);
                        ASSERT_EXCLUSIVE_ACCESS_SCOPED(test_scoped);
                        BUG_ON(!current->kcsan_ctx.scoped_accesses.prev);
                        /* Unrelated accesses. */
                        __kcsan_check_access(&cycles, sizeof(cycles), 0);
                        __kcsan_check_access(&cycles, sizeof(cycles), KCSAN_ACCESS_ATOMIC);
                }
                BUG_ON(current->kcsan_ctx.scoped_accesses.prev);
        }
        cycles = get_cycles() - cycles;

        pr_info("KCSAN: %s end   | cycles: %llu\n", __func__, cycles);

        /* restore context */
        current->kcsan_ctx = ctx_save;
}

static int cmp_filterlist_addrs(const void *rhs, const void *lhs)
{
        const unsigned long a = *(const unsigned long *)rhs;
        const unsigned long b = *(const unsigned long *)lhs;

        return a < b ? -1 : a == b ? 0 : 1;
}

bool kcsan_skip_report_debugfs(unsigned long func_addr)
{
        unsigned long symbolsize, offset;
        unsigned long flags;
        bool ret = false;

        if (!kallsyms_lookup_size_offset(func_addr, &symbolsize, &offset))
                return false;
        func_addr -= offset; /* Get function start */

        spin_lock_irqsave(&report_filterlist_lock, flags);
        if (report_filterlist.used == 0)
                goto out;

        /* Sort array if it is unsorted, and then do a binary search. */
        if (!report_filterlist.sorted) {
                sort(report_filterlist.addrs, report_filterlist.used,
                     sizeof(unsigned long), cmp_filterlist_addrs, NULL);
                report_filterlist.sorted = true;
        }
        ret = !!bsearch(&func_addr, report_filterlist.addrs,
                        report_filterlist.used, sizeof(unsigned long),
                        cmp_filterlist_addrs);
        if (report_filterlist.whitelist)
                ret = !ret;

out:
        spin_unlock_irqrestore(&report_filterlist_lock, flags);
        return ret;
}

static void set_report_filterlist_whitelist(bool whitelist)
{
        unsigned long flags;

        spin_lock_irqsave(&report_filterlist_lock, flags);
        report_filterlist.whitelist = whitelist;
        spin_unlock_irqrestore(&report_filterlist_lock, flags);
}

/* Returns 0 on success, error-code otherwise. */
static ssize_t insert_report_filterlist(const char *func)
{
        unsigned long flags;
        unsigned long addr = kallsyms_lookup_name(func);
        ssize_t ret = 0;

        if (!addr) {
                pr_err("KCSAN: could not find function: '%s'\n", func);
                return -ENOENT;
        }

        spin_lock_irqsave(&report_filterlist_lock, flags);

        if (report_filterlist.addrs == NULL) {
                /* initial allocation */
                report_filterlist.addrs =
                        kmalloc_array(report_filterlist.size,
                                      sizeof(unsigned long), GFP_ATOMIC);
                if (report_filterlist.addrs == NULL) {
                        ret = -ENOMEM;
                        goto out;
                }
        } else if (report_filterlist.used == report_filterlist.size) {
                /* resize filterlist */
                size_t new_size = report_filterlist.size * 2;
                unsigned long *new_addrs =
                        krealloc(report_filterlist.addrs,
                                 new_size * sizeof(unsigned long), GFP_ATOMIC);

                if (new_addrs == NULL) {
                        /* leave filterlist itself untouched */
                        ret = -ENOMEM;
                        goto out;
                }

                report_filterlist.size = new_size;
                report_filterlist.addrs = new_addrs;
        }

        /* Note: deduplicating should be done in userspace. */
        report_filterlist.addrs[report_filterlist.used++] =
                kallsyms_lookup_name(func);
        report_filterlist.sorted = false;

out:
        spin_unlock_irqrestore(&report_filterlist_lock, flags);

        return ret;
}

static int show_info(struct seq_file *file, void *v)
{
        int i;
        unsigned long flags;

        /* show stats */
        seq_printf(file, "enabled: %i\n", READ_ONCE(kcsan_enabled));
        for (i = 0; i < KCSAN_COUNTER_COUNT; ++i)
                seq_printf(file, "%s: %ld\n", counter_to_name(i),
                           atomic_long_read(&counters[i]));

        /* show filter functions, and filter type */
        spin_lock_irqsave(&report_filterlist_lock, flags);
        seq_printf(file, "\n%s functions: %s\n",
                   report_filterlist.whitelist ? "whitelisted" : "blacklisted",
                   report_filterlist.used == 0 ? "none" : "");
        for (i = 0; i < report_filterlist.used; ++i)
                seq_printf(file, " %ps\n", (void *)report_filterlist.addrs[i]);
        spin_unlock_irqrestore(&report_filterlist_lock, flags);

        return 0;
}

static int debugfs_open(struct inode *inode, struct file *file)
{
        return single_open(file, show_info, NULL);
}

static ssize_t
debugfs_write(struct file *file, const char __user *buf, size_t count, loff_t *off)
{
        char kbuf[KSYM_NAME_LEN];
        char *arg;
        int read_len = count < (sizeof(kbuf) - 1) ? count : (sizeof(kbuf) - 1);

        if (copy_from_user(kbuf, buf, read_len))
                return -EFAULT;
        kbuf[read_len] = '\0';
        arg = strstrip(kbuf);

        if (!strcmp(arg, "on")) {
                WRITE_ONCE(kcsan_enabled, true);
        } else if (!strcmp(arg, "off")) {
                WRITE_ONCE(kcsan_enabled, false);
        } else if (!strncmp(arg, "microbench=", sizeof("microbench=") - 1)) {
                unsigned long iters;

                if (kstrtoul(&arg[sizeof("microbench=") - 1], 0, &iters))
                        return -EINVAL;
                microbenchmark(iters);
        } else if (!strncmp(arg, "test=", sizeof("test=") - 1)) {
                unsigned long iters;

                if (kstrtoul(&arg[sizeof("test=") - 1], 0, &iters))
                        return -EINVAL;
                test_thread(iters);
        } else if (!strcmp(arg, "whitelist")) {
                set_report_filterlist_whitelist(true);
        } else if (!strcmp(arg, "blacklist")) {
                set_report_filterlist_whitelist(false);
        } else if (arg[0] == '!') {
                ssize_t ret = insert_report_filterlist(&arg[1]);

                if (ret < 0)
                        return ret;
        } else {
                return -EINVAL;
        }

        return count;
}

static const struct file_operations debugfs_ops =
{
        .read    = seq_read,
        .open    = debugfs_open,
        .write   = debugfs_write,
        .release = single_release
};

void __init kcsan_debugfs_init(void)
{
        debugfs_create_file("kcsan", 0644, NULL, NULL, &debugfs_ops);
}