// SPDX-License-Identifier: GPL-2.0
/*
 * This is for all the tests related to refcount bugs (e.g. overflow,
 * underflow, reaching zero untested, etc).
 */
#include "lkdtm.h"
#include <linux/refcount.h>

static void overflow_check(refcount_t *ref)
{
        switch (refcount_read(ref)) {
        case REFCOUNT_SATURATED:
                pr_info("Overflow detected: saturated\n");
                break;
        case REFCOUNT_MAX:
                pr_warn("Overflow detected: unsafely reset to max\n");
                break;
        default:
                pr_err("Fail: refcount wrapped to %d\n", refcount_read(ref));
        }
}

/*
 * A refcount_inc() above the maximum value of the refcount implementation,
 * should at least saturate, and at most also WARN.
 */
void lkdtm_REFCOUNT_INC_OVERFLOW(void)
{
        refcount_t over = REFCOUNT_INIT(REFCOUNT_MAX - 1);

        pr_info("attempting good refcount_inc() without overflow\n");
        refcount_dec(&over);
        refcount_inc(&over);

        pr_info("attempting bad refcount_inc() overflow\n");
        refcount_inc(&over);
        refcount_inc(&over);

        overflow_check(&over);
}

/* refcount_add() should behave just like refcount_inc() above. */
void lkdtm_REFCOUNT_ADD_OVERFLOW(void)
{
        refcount_t over = REFCOUNT_INIT(REFCOUNT_MAX - 1);

        pr_info("attempting good refcount_add() without overflow\n");
        refcount_dec(&over);
        refcount_dec(&over);
        refcount_dec(&over);
        refcount_dec(&over);
        refcount_add(4, &over);

        pr_info("attempting bad refcount_add() overflow\n");
        refcount_add(4, &over);

        overflow_check(&over);
}

/* refcount_inc_not_zero() should behave just like refcount_inc() above. */
void lkdtm_REFCOUNT_INC_NOT_ZERO_OVERFLOW(void)
{
        refcount_t over = REFCOUNT_INIT(REFCOUNT_MAX);

        pr_info("attempting bad refcount_inc_not_zero() overflow\n");
        if (!refcount_inc_not_zero(&over))
                pr_warn("Weird: refcount_inc_not_zero() reported zero\n");

        overflow_check(&over);
}

/* refcount_add_not_zero() should behave just like refcount_inc() above. */
void lkdtm_REFCOUNT_ADD_NOT_ZERO_OVERFLOW(void)
{
        refcount_t over = REFCOUNT_INIT(REFCOUNT_MAX);

        pr_info("attempting bad refcount_add_not_zero() overflow\n");
        if (!refcount_add_not_zero(6, &over))
                pr_warn("Weird: refcount_add_not_zero() reported zero\n");

        overflow_check(&over);
}

static void check_zero(refcount_t *ref)
{
        switch (refcount_read(ref)) {
        case REFCOUNT_SATURATED:
                pr_info("Zero detected: saturated\n");
                break;
        case REFCOUNT_MAX:
                pr_warn("Zero detected: unsafely reset to max\n");
                break;
        case 0:
                pr_warn("Still at zero: refcount_inc/add() must not inc-from-0\n");
                break;
        default:
                pr_err("Fail: refcount went crazy: %d\n", refcount_read(ref));
        }
}

/*
 * A refcount_dec(), as opposed to a refcount_dec_and_test(), when it hits
 * zero it should either saturate (when inc-from-zero isn't protected)
 * or stay at zero (when inc-from-zero is protected) and should WARN for both.
 */
void lkdtm_REFCOUNT_DEC_ZERO(void)
{
        refcount_t zero = REFCOUNT_INIT(2);

        pr_info("attempting good refcount_dec()\n");
        refcount_dec(&zero);

        pr_info("attempting bad refcount_dec() to zero\n");
        refcount_dec(&zero);

        check_zero(&zero);
}

static void check_negative(refcount_t *ref, int start)
{
        /*
         * refcount_t refuses to move a refcount at all on an
         * over-sub, so we have to track our starting position instead of
         * looking only at zero-pinning.
         */
        if (refcount_read(ref) == start) {
                pr_warn("Still at %d: refcount_inc/add() must not inc-from-0\n",
                        start);
                return;
        }

        switch (refcount_read(ref)) {
        case REFCOUNT_SATURATED:
                pr_info("Negative detected: saturated\n");
                break;
        case REFCOUNT_MAX:
                pr_warn("Negative detected: unsafely reset to max\n");
                break;
        default:
                pr_err("Fail: refcount went crazy: %d\n", refcount_read(ref));
        }
}

/* A refcount_dec() going negative should saturate and may WARN. */
void lkdtm_REFCOUNT_DEC_NEGATIVE(void)
{
        refcount_t neg = REFCOUNT_INIT(0);

        pr_info("attempting bad refcount_dec() below zero\n");
        refcount_dec(&neg);

        check_negative(&neg, 0);
}

/*
 * A refcount_dec_and_test() should act like refcount_dec() above when
 * going negative.
 */
void lkdtm_REFCOUNT_DEC_AND_TEST_NEGATIVE(void)
{
        refcount_t neg = REFCOUNT_INIT(0);

        pr_info("attempting bad refcount_dec_and_test() below zero\n");
        if (refcount_dec_and_test(&neg))
                pr_warn("Weird: refcount_dec_and_test() reported zero\n");

        check_negative(&neg, 0);
}

/*
 * A refcount_sub_and_test() should act like refcount_dec_and_test()
 * above when going negative.
 */
void lkdtm_REFCOUNT_SUB_AND_TEST_NEGATIVE(void)
{
        refcount_t neg = REFCOUNT_INIT(3);

        pr_info("attempting bad refcount_sub_and_test() below zero\n");
        if (refcount_sub_and_test(5, &neg))
                pr_warn("Weird: refcount_sub_and_test() reported zero\n");

        check_negative(&neg, 3);
}

static void check_from_zero(refcount_t *ref)
{
        switch (refcount_read(ref)) {
        case 0:
                pr_info("Zero detected: stayed at zero\n");
                break;
        case REFCOUNT_SATURATED:
                pr_info("Zero detected: saturated\n");
                break;
        case REFCOUNT_MAX:
                pr_warn("Zero detected: unsafely reset to max\n");
                break;
        default:
                pr_info("Fail: zero not detected, incremented to %d\n",
                        refcount_read(ref));
        }
}

/*
 * A refcount_inc() from zero should pin to zero or saturate and may WARN.
 */
void lkdtm_REFCOUNT_INC_ZERO(void)
{
        refcount_t zero = REFCOUNT_INIT(0);

        pr_info("attempting safe refcount_inc_not_zero() from zero\n");
        if (!refcount_inc_not_zero(&zero)) {
                pr_info("Good: zero detected\n");
                if (refcount_read(&zero) == 0)
                        pr_info("Correctly stayed at zero\n");
                else
                        pr_err("Fail: refcount went past zero!\n");
        } else {
                pr_err("Fail: Zero not detected!?\n");
        }

        pr_info("attempting bad refcount_inc() from zero\n");
        refcount_inc(&zero);

        check_from_zero(&zero);
}

/*
 * A refcount_add() should act like refcount_inc() above when starting
 * at zero.
 */
void lkdtm_REFCOUNT_ADD_ZERO(void)
{
        refcount_t zero = REFCOUNT_INIT(0);

        pr_info("attempting safe refcount_add_not_zero() from zero\n");
        if (!refcount_add_not_zero(3, &zero)) {
                pr_info("Good: zero detected\n");
                if (refcount_read(&zero) == 0)
                        pr_info("Correctly stayed at zero\n");
                else
                        pr_err("Fail: refcount went past zero\n");
        } else {
                pr_err("Fail: Zero not detected!?\n");
        }

        pr_info("attempting bad refcount_add() from zero\n");
        refcount_add(3, &zero);

        check_from_zero(&zero);
}

static void check_saturated(refcount_t *ref)
{
        switch (refcount_read(ref)) {
        case REFCOUNT_SATURATED:
                pr_info("Saturation detected: still saturated\n");
                break;
        case REFCOUNT_MAX:
                pr_warn("Saturation detected: unsafely reset to max\n");
                break;
        default:
                pr_err("Fail: refcount went crazy: %d\n", refcount_read(ref));
        }
}

/*
 * A refcount_inc() from a saturated value should at most warn about
 * being saturated already.
 */
void lkdtm_REFCOUNT_INC_SATURATED(void)
{
        refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);

        pr_info("attempting bad refcount_inc() from saturated\n");
        refcount_inc(&sat);

        check_saturated(&sat);
}

/* Should act like refcount_inc() above from saturated. */
void lkdtm_REFCOUNT_DEC_SATURATED(void)
{
        refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);

        pr_info("attempting bad refcount_dec() from saturated\n");
        refcount_dec(&sat);

        check_saturated(&sat);
}

/* Should act like refcount_inc() above from saturated. */
void lkdtm_REFCOUNT_ADD_SATURATED(void)
{
        refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);

        pr_info("attempting bad refcount_dec() from saturated\n");
        refcount_add(8, &sat);

        check_saturated(&sat);
}

/* Should act like refcount_inc() above from saturated. */
void lkdtm_REFCOUNT_INC_NOT_ZERO_SATURATED(void)
{
        refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);

        pr_info("attempting bad refcount_inc_not_zero() from saturated\n");
        if (!refcount_inc_not_zero(&sat))
                pr_warn("Weird: refcount_inc_not_zero() reported zero\n");

        check_saturated(&sat);
}

/* Should act like refcount_inc() above from saturated. */
void lkdtm_REFCOUNT_ADD_NOT_ZERO_SATURATED(void)
{
        refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);

        pr_info("attempting bad refcount_add_not_zero() from saturated\n");
        if (!refcount_add_not_zero(7, &sat))
                pr_warn("Weird: refcount_add_not_zero() reported zero\n");

        check_saturated(&sat);
}

/* Should act like refcount_inc() above from saturated. */
void lkdtm_REFCOUNT_DEC_AND_TEST_SATURATED(void)
{
        refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);

        pr_info("attempting bad refcount_dec_and_test() from saturated\n");
        if (refcount_dec_and_test(&sat))
                pr_warn("Weird: refcount_dec_and_test() reported zero\n");

        check_saturated(&sat);
}

/* Should act like refcount_inc() above from saturated. */
void lkdtm_REFCOUNT_SUB_AND_TEST_SATURATED(void)
{
        refcount_t sat = REFCOUNT_INIT(REFCOUNT_SATURATED);

        pr_info("attempting bad refcount_sub_and_test() from saturated\n");
        if (refcount_sub_and_test(8, &sat))
                pr_warn("Weird: refcount_sub_and_test() reported zero\n");

        check_saturated(&sat);
}

/* Used to time the existing atomic_t when used for reference counting */
void lkdtm_ATOMIC_TIMING(void)
{
        unsigned int i;
        atomic_t count = ATOMIC_INIT(1);

        for (i = 0; i < INT_MAX - 1; i++)
                atomic_inc(&count);

        for (i = INT_MAX; i > 0; i--)
                if (atomic_dec_and_test(&count))
                        break;

        if (i != 1)
                pr_err("atomic timing: out of sync up/down cycle: %u\n", i - 1);
        else
                pr_info("atomic timing: done\n");
}

/*
 * This can be compared to ATOMIC_TIMING when implementing fast refcount
 * protections. Looking at the number of CPU cycles tells the real story
 * about performance. For example:
 *    cd /sys/kernel/debug/provoke-crash
 *    perf stat -B -- cat <(echo REFCOUNT_TIMING) > DIRECT
 */
void lkdtm_REFCOUNT_TIMING(void)
{
        unsigned int i;
        refcount_t count = REFCOUNT_INIT(1);

        for (i = 0; i < INT_MAX - 1; i++)
                refcount_inc(&count);

        for (i = INT_MAX; i > 0; i--)
                if (refcount_dec_and_test(&count))
                        break;

        if (i != 1)
                pr_err("refcount: out of sync up/down cycle: %u\n", i - 1);
        else
                pr_info("refcount timing: done\n");
}