/* Copyright (c) 2016 Facebook
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of version 2 of the GNU General Public
   * License as published by the Free Software Foundation.
   */
  #include <linux/bpf.h>
  #include <linux/jhash.h>
  #include <linux/filter.h>

  #include <linux/stacktrace.h>
  #include <linux/perf_event.h>

  #include "percpu_freelist.h"

  
  struct stack_map_bucket {

  	struct pcpu_freelist_node fnode;

  	u32 hash;
  	u32 nr;
  	u64 ip[];
  };
  
  struct bpf_stack_map {
  	struct bpf_map map;

  	void *elems;
  	struct pcpu_freelist freelist;

  	u32 n_buckets;

  	struct stack_map_bucket *buckets[];

  };

  static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
  {
  	u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size;
  	int err;

  	smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries);

  	if (!smap->elems)
  		return -ENOMEM;
  
  	err = pcpu_freelist_init(&smap->freelist);
  	if (err)
  		goto free_elems;
  
  	pcpu_freelist_populate(&smap->freelist, smap->elems, elem_size,
  			       smap->map.max_entries);
  	return 0;
  
  free_elems:

  	bpf_map_area_free(smap->elems);

  	return err;
  }

  /* Called from syscall */
  static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
  {
  	u32 value_size = attr->value_size;
  	struct bpf_stack_map *smap;
  	u64 cost, n_buckets;
  	int err;
  
  	if (!capable(CAP_SYS_ADMIN))
  		return ERR_PTR(-EPERM);

  	if (attr->map_flags)
  		return ERR_PTR(-EINVAL);

  	/* check sanity of attributes */
  	if (attr->max_entries == 0 || attr->key_size != 4 ||
  	    value_size < 8 || value_size % 8 ||

  	    value_size / 8 > sysctl_perf_event_max_stack)

  		return ERR_PTR(-EINVAL);
  
  	/* hash table size must be power of 2 */
  	n_buckets = roundup_pow_of_two(attr->max_entries);
  
  	cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
  	if (cost >= U32_MAX - PAGE_SIZE)
  		return ERR_PTR(-E2BIG);

  	smap = bpf_map_area_alloc(cost);
  	if (!smap)
  		return ERR_PTR(-ENOMEM);

  
  	err = -E2BIG;
  	cost += n_buckets * (value_size + sizeof(struct stack_map_bucket));
  	if (cost >= U32_MAX - PAGE_SIZE)
  		goto free_smap;
  
  	smap->map.map_type = attr->map_type;
  	smap->map.key_size = attr->key_size;
  	smap->map.value_size = value_size;
  	smap->map.max_entries = attr->max_entries;

  	smap->map.map_flags = attr->map_flags;

  	smap->n_buckets = n_buckets;
  	smap->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;

  	err = bpf_map_precharge_memlock(smap->map.pages);
  	if (err)
  		goto free_smap;

  	err = get_callchain_buffers(sysctl_perf_event_max_stack);

  	if (err)
  		goto free_smap;

  	err = prealloc_elems_and_freelist(smap);
  	if (err)
  		goto put_buffers;

  	return &smap->map;

  put_buffers:
  	put_callchain_buffers();

  free_smap:

  	bpf_map_area_free(smap);

  	return ERR_PTR(err);
  }

  BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
  	   u64, flags)

  {

  	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
  	struct perf_callchain_entry *trace;
  	struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
  	u32 max_depth = map->value_size / 8;

  	/* stack_map_alloc() checks that max_depth <= sysctl_perf_event_max_stack */
  	u32 init_nr = sysctl_perf_event_max_stack - max_depth;

  	u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
  	u32 hash, id, trace_nr, trace_len;
  	bool user = flags & BPF_F_USER_STACK;
  	bool kernel = !user;
  	u64 *ips;
  
  	if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
  			       BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
  		return -EINVAL;

  	trace = get_perf_callchain(regs, init_nr, kernel, user,
  				   sysctl_perf_event_max_stack, false, false);

  
  	if (unlikely(!trace))
  		/* couldn't fetch the stack trace */
  		return -EFAULT;
  
  	/* get_perf_callchain() guarantees that trace->nr >= init_nr

  	 * and trace-nr <= sysctl_perf_event_max_stack, so trace_nr <= max_depth

  	 */
  	trace_nr = trace->nr - init_nr;
  
  	if (trace_nr <= skip)
  		/* skipping more than usable stack trace */
  		return -EFAULT;
  
  	trace_nr -= skip;
  	trace_len = trace_nr * sizeof(u64);
  	ips = trace->ip + skip + init_nr;
  	hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0);
  	id = hash & (smap->n_buckets - 1);

  	bucket = READ_ONCE(smap->buckets[id]);

  
  	if (bucket && bucket->hash == hash) {
  		if (flags & BPF_F_FAST_STACK_CMP)
  			return id;
  		if (bucket->nr == trace_nr &&
  		    memcmp(bucket->ip, ips, trace_len) == 0)
  			return id;
  	}
  
  	/* this call stack is not in the map, try to add it */
  	if (bucket && !(flags & BPF_F_REUSE_STACKID))
  		return -EEXIST;

  	new_bucket = (struct stack_map_bucket *)
  		pcpu_freelist_pop(&smap->freelist);

  	if (unlikely(!new_bucket))
  		return -ENOMEM;
  
  	memcpy(new_bucket->ip, ips, trace_len);

  	new_bucket->hash = hash;
  	new_bucket->nr = trace_nr;
  
  	old_bucket = xchg(&smap->buckets[id], new_bucket);
  	if (old_bucket)

  		pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);

  	return id;
  }
  
  const struct bpf_func_proto bpf_get_stackid_proto = {
  	.func		= bpf_get_stackid,
  	.gpl_only	= true,
  	.ret_type	= RET_INTEGER,
  	.arg1_type	= ARG_PTR_TO_CTX,
  	.arg2_type	= ARG_CONST_MAP_PTR,
  	.arg3_type	= ARG_ANYTHING,
  };

  /* Called from eBPF program */

  static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
  {

  	return NULL;
  }
  
  /* Called from syscall */
  int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
  {

  	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);

  	struct stack_map_bucket *bucket, *old_bucket;
  	u32 id = *(u32 *)key, trace_len;

  
  	if (unlikely(id >= smap->n_buckets))

  		return -ENOENT;
  
  	bucket = xchg(&smap->buckets[id], NULL);
  	if (!bucket)
  		return -ENOENT;
  
  	trace_len = bucket->nr * sizeof(u64);
  	memcpy(value, bucket->ip, trace_len);
  	memset(value + trace_len, 0, map->value_size - trace_len);
  
  	old_bucket = xchg(&smap->buckets[id], bucket);
  	if (old_bucket)
  		pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
  	return 0;

  }
  
  static int stack_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
  {
  	return -EINVAL;
  }
  
  static int stack_map_update_elem(struct bpf_map *map, void *key, void *value,
  				 u64 map_flags)
  {
  	return -EINVAL;
  }
  
  /* Called from syscall or from eBPF program */
  static int stack_map_delete_elem(struct bpf_map *map, void *key)
  {
  	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
  	struct stack_map_bucket *old_bucket;
  	u32 id = *(u32 *)key;
  
  	if (unlikely(id >= smap->n_buckets))
  		return -E2BIG;
  
  	old_bucket = xchg(&smap->buckets[id], NULL);
  	if (old_bucket) {

  		pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);

  		return 0;
  	} else {
  		return -ENOENT;
  	}
  }
  
  /* Called when map->refcnt goes to zero, either from workqueue or from syscall */
  static void stack_map_free(struct bpf_map *map)
  {
  	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);

  	/* wait for bpf programs to complete before freeing stack map */

  	synchronize_rcu();

  	bpf_map_area_free(smap->elems);

  	pcpu_freelist_destroy(&smap->freelist);

  	bpf_map_area_free(smap);

  	put_callchain_buffers();
  }
  
  static const struct bpf_map_ops stack_map_ops = {
  	.map_alloc = stack_map_alloc,
  	.map_free = stack_map_free,
  	.map_get_next_key = stack_map_get_next_key,
  	.map_lookup_elem = stack_map_lookup_elem,
  	.map_update_elem = stack_map_update_elem,
  	.map_delete_elem = stack_map_delete_elem,
  };
  
  static struct bpf_map_type_list stack_map_type __read_mostly = {
  	.ops = &stack_map_ops,
  	.type = BPF_MAP_TYPE_STACK_TRACE,
  };
  
  static int __init register_stack_map(void)
  {
  	bpf_register_map_type(&stack_map_type);
  	return 0;
  }
  late_initcall(register_stack_map);