// SPDX-License-Identifier: GPL-2.0
/*
 * queue_stack_maps.c: BPF queue and stack maps
 *
 * Copyright (c) 2018 Politecnico di Torino
 */
#include <linux/bpf.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/capability.h>
#include "percpu_freelist.h"

#define QUEUE_STACK_CREATE_FLAG_MASK \
        (BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)


struct bpf_queue_stack {
        struct bpf_map map;
        raw_spinlock_t lock;
        u32 head, tail;
        u32 size; /* max_entries + 1 */

        char elements[0] __aligned(8);
};

static struct bpf_queue_stack *bpf_queue_stack(struct bpf_map *map)
{
        return container_of(map, struct bpf_queue_stack, map);
}

static bool queue_stack_map_is_empty(struct bpf_queue_stack *qs)
{
        return qs->head == qs->tail;
}

static bool queue_stack_map_is_full(struct bpf_queue_stack *qs)
{
        u32 head = qs->head + 1;

        if (unlikely(head >= qs->size))
                head = 0;

        return head == qs->tail;
}

/* Called from syscall */
static int queue_stack_map_alloc_check(union bpf_attr *attr)
{
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        /* check sanity of attributes */
        if (attr->max_entries == 0 || attr->key_size != 0 ||
            attr->value_size == 0 ||
            attr->map_flags & ~QUEUE_STACK_CREATE_FLAG_MASK)
                return -EINVAL;

        if (attr->value_size > KMALLOC_MAX_SIZE)
                /* if value_size is bigger, the user space won't be able to
                 * access the elements.
                 */
                return -E2BIG;

        return 0;
}

static struct bpf_map *queue_stack_map_alloc(union bpf_attr *attr)
{
        int ret, numa_node = bpf_map_attr_numa_node(attr);
        struct bpf_queue_stack *qs;
        u64 size, queue_size, cost;

        size = (u64) attr->max_entries + 1;
        cost = queue_size = sizeof(*qs) + size * attr->value_size;
        if (cost >= U32_MAX - PAGE_SIZE)
                return ERR_PTR(-E2BIG);

        cost = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;

        ret = bpf_map_precharge_memlock(cost);
        if (ret < 0)
                return ERR_PTR(ret);

        qs = bpf_map_area_alloc(queue_size, numa_node);
        if (!qs)
                return ERR_PTR(-ENOMEM);

        memset(qs, 0, sizeof(*qs));

        bpf_map_init_from_attr(&qs->map, attr);

        qs->map.pages = cost;
        qs->size = size;

        raw_spin_lock_init(&qs->lock);

        return &qs->map;
}

/* Called when map->refcnt goes to zero, either from workqueue or from syscall */
static void queue_stack_map_free(struct bpf_map *map)
{
        struct bpf_queue_stack *qs = bpf_queue_stack(map);

        /* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
         * so the programs (can be more than one that used this map) were
         * disconnected from events. Wait for outstanding critical sections in
         * these programs to complete
         */
        synchronize_rcu();

        bpf_map_area_free(qs);
}

static int __queue_map_get(struct bpf_map *map, void *value, bool delete)
{
        struct bpf_queue_stack *qs = bpf_queue_stack(map);
        unsigned long flags;
        int err = 0;
        void *ptr;

        raw_spin_lock_irqsave(&qs->lock, flags);

        if (queue_stack_map_is_empty(qs)) {
                memset(value, 0, qs->map.value_size);
                err = -ENOENT;
                goto out;
        }

        ptr = &qs->elements[qs->tail * qs->map.value_size];
        memcpy(value, ptr, qs->map.value_size);

        if (delete) {
                if (unlikely(++qs->tail >= qs->size))
                        qs->tail = 0;
        }

out:
        raw_spin_unlock_irqrestore(&qs->lock, flags);
        return err;
}


static int __stack_map_get(struct bpf_map *map, void *value, bool delete)
{
        struct bpf_queue_stack *qs = bpf_queue_stack(map);
        unsigned long flags;
        int err = 0;
        void *ptr;
        u32 index;

        raw_spin_lock_irqsave(&qs->lock, flags);

        if (queue_stack_map_is_empty(qs)) {
                memset(value, 0, qs->map.value_size);
                err = -ENOENT;
                goto out;
        }

        index = qs->head - 1;
        if (unlikely(index >= qs->size))
                index = qs->size - 1;

        ptr = &qs->elements[index * qs->map.value_size];
        memcpy(value, ptr, qs->map.value_size);

        if (delete)
                qs->head = index;

out:
        raw_spin_unlock_irqrestore(&qs->lock, flags);
        return err;
}

/* Called from syscall or from eBPF program */
static int queue_map_peek_elem(struct bpf_map *map, void *value)
{
        return __queue_map_get(map, value, false);
}

/* Called from syscall or from eBPF program */
static int stack_map_peek_elem(struct bpf_map *map, void *value)
{
        return __stack_map_get(map, value, false);
}

/* Called from syscall or from eBPF program */
static int queue_map_pop_elem(struct bpf_map *map, void *value)
{
        return __queue_map_get(map, value, true);
}

/* Called from syscall or from eBPF program */
static int stack_map_pop_elem(struct bpf_map *map, void *value)
{
        return __stack_map_get(map, value, true);
}

/* Called from syscall or from eBPF program */
static int queue_stack_map_push_elem(struct bpf_map *map, void *value,
                                     u64 flags)
{
        struct bpf_queue_stack *qs = bpf_queue_stack(map);
        unsigned long irq_flags;
        int err = 0;
        void *dst;

        /* BPF_EXIST is used to force making room for a new element in case the
         * map is full
         */
        bool replace = (flags & BPF_EXIST);

        /* Check supported flags for queue and stack maps */
        if (flags & BPF_NOEXIST || flags > BPF_EXIST)
                return -EINVAL;

        raw_spin_lock_irqsave(&qs->lock, irq_flags);

        if (queue_stack_map_is_full(qs)) {
                if (!replace) {
                        err = -E2BIG;
                        goto out;
                }
                /* advance tail pointer to overwrite oldest element */
                if (unlikely(++qs->tail >= qs->size))
                        qs->tail = 0;
        }

        dst = &qs->elements[qs->head * qs->map.value_size];
        memcpy(dst, value, qs->map.value_size);

        if (unlikely(++qs->head >= qs->size))
                qs->head = 0;

out:
        raw_spin_unlock_irqrestore(&qs->lock, irq_flags);
        return err;
}

/* Called from syscall or from eBPF program */
static void *queue_stack_map_lookup_elem(struct bpf_map *map, void *key)
{
        return NULL;
}

/* Called from syscall or from eBPF program */
static int queue_stack_map_update_elem(struct bpf_map *map, void *key,
                                       void *value, u64 flags)
{
        return -EINVAL;
}

/* Called from syscall or from eBPF program */
static int queue_stack_map_delete_elem(struct bpf_map *map, void *key)
{
        return -EINVAL;
}

/* Called from syscall */
static int queue_stack_map_get_next_key(struct bpf_map *map, void *key,
                                        void *next_key)
{
        return -EINVAL;
}

const struct bpf_map_ops queue_map_ops = {
        .map_alloc_check = queue_stack_map_alloc_check,
        .map_alloc = queue_stack_map_alloc,
        .map_free = queue_stack_map_free,
        .map_lookup_elem = queue_stack_map_lookup_elem,
        .map_update_elem = queue_stack_map_update_elem,
        .map_delete_elem = queue_stack_map_delete_elem,
        .map_push_elem = queue_stack_map_push_elem,
        .map_pop_elem = queue_map_pop_elem,
        .map_peek_elem = queue_map_peek_elem,
        .map_get_next_key = queue_stack_map_get_next_key,
};

const struct bpf_map_ops stack_map_ops = {
        .map_alloc_check = queue_stack_map_alloc_check,
        .map_alloc = queue_stack_map_alloc,
        .map_free = queue_stack_map_free,
        .map_lookup_elem = queue_stack_map_lookup_elem,
        .map_update_elem = queue_stack_map_update_elem,
        .map_delete_elem = queue_stack_map_delete_elem,
        .map_push_elem = queue_stack_map_push_elem,
        .map_pop_elem = stack_map_pop_elem,
        .map_peek_elem = stack_map_peek_elem,
        .map_get_next_key = queue_stack_map_get_next_key,
};