/* 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 <linux/elf.h>
#include <linux/pagemap.h>
#include "percpu_freelist.h"

#define STACK_CREATE_FLAG_MASK                                  \
        (BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY |        \
         BPF_F_STACK_BUILD_ID)

struct stack_map_bucket {
        struct pcpu_freelist_node fnode;
        u32 hash;
        u32 nr;
        u64 data[];
};

struct bpf_stack_map {
        struct bpf_map map;
        void *elems;
        struct pcpu_freelist freelist;
        u32 n_buckets;
        struct stack_map_bucket *buckets[];
};

static inline bool stack_map_use_build_id(struct bpf_map *map)
{
        return (map->map_flags & BPF_F_STACK_BUILD_ID);
}

static inline int stack_map_data_size(struct bpf_map *map)
{
        return stack_map_use_build_id(map) ?
                sizeof(struct bpf_stack_build_id) : sizeof(u64);
}

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,
                                         smap->map.numa_node);
        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 & ~STACK_CREATE_FLAG_MASK)
                return ERR_PTR(-EINVAL);

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

        BUILD_BUG_ON(sizeof(struct bpf_stack_build_id) % sizeof(u64));
        if (attr->map_flags & BPF_F_STACK_BUILD_ID) {
                if (value_size % sizeof(struct bpf_stack_build_id) ||
                    value_size / sizeof(struct bpf_stack_build_id)
                    > sysctl_perf_event_max_stack)
                        return ERR_PTR(-EINVAL);
        } else if (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, bpf_map_attr_numa_node(attr));
        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;

        bpf_map_init_from_attr(&smap->map, attr);
        smap->map.value_size = value_size;
        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);
}

#define BPF_BUILD_ID 3
/*
 * Parse build id from the note segment. This logic can be shared between
 * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
 * identical.
 */
static inline int stack_map_parse_build_id(void *page_addr,
                                           unsigned char *build_id,
                                           void *note_start,
                                           Elf32_Word note_size)
{
        Elf32_Word note_offs = 0, new_offs;

        /* check for overflow */
        if (note_start < page_addr || note_start + note_size < note_start)
                return -EINVAL;

        /* only supports note that fits in the first page */
        if (note_start + note_size > page_addr + PAGE_SIZE)
                return -EINVAL;

        while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
                Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);

                if (nhdr->n_type == BPF_BUILD_ID &&
                    nhdr->n_namesz == sizeof("GNU") &&
                    nhdr->n_descsz == BPF_BUILD_ID_SIZE) {
                        memcpy(build_id,
                               note_start + note_offs +
                               ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
                               BPF_BUILD_ID_SIZE);
                        return 0;
                }
                new_offs = note_offs + sizeof(Elf32_Nhdr) +
                        ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4);
                if (new_offs <= note_offs)  /* overflow */
                        break;
                note_offs = new_offs;
        }
        return -EINVAL;
}

/* Parse build ID from 32-bit ELF */
static int stack_map_get_build_id_32(void *page_addr,
                                     unsigned char *build_id)
{
        Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr;
        Elf32_Phdr *phdr;
        int i;

        /* only supports phdr that fits in one page */
        if (ehdr->e_phnum >
            (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
                return -EINVAL;

        phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr));

        for (i = 0; i < ehdr->e_phnum; ++i)
                if (phdr[i].p_type == PT_NOTE)
                        return stack_map_parse_build_id(page_addr, build_id,
                                        page_addr + phdr[i].p_offset,
                                        phdr[i].p_filesz);
        return -EINVAL;
}

/* Parse build ID from 64-bit ELF */
static int stack_map_get_build_id_64(void *page_addr,
                                     unsigned char *build_id)
{
        Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
        Elf64_Phdr *phdr;
        int i;

        /* only supports phdr that fits in one page */
        if (ehdr->e_phnum >
            (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
                return -EINVAL;

        phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr));

        for (i = 0; i < ehdr->e_phnum; ++i)
                if (phdr[i].p_type == PT_NOTE)
                        return stack_map_parse_build_id(page_addr, build_id,
                                        page_addr + phdr[i].p_offset,
                                        phdr[i].p_filesz);
        return -EINVAL;
}

/* Parse build ID of ELF file mapped to vma */
static int stack_map_get_build_id(struct vm_area_struct *vma,
                                  unsigned char *build_id)
{
        Elf32_Ehdr *ehdr;
        struct page *page;
        void *page_addr;
        int ret;

        /* only works for page backed storage  */
        if (!vma->vm_file)
                return -EINVAL;

        page = find_get_page(vma->vm_file->f_mapping, 0);
        if (!page)
                return -EFAULT; /* page not mapped */

        ret = -EINVAL;
        page_addr = page_address(page);
        ehdr = (Elf32_Ehdr *)page_addr;

        /* compare magic x7f "ELF" */
        if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
                goto out;

        /* only support executable file and shared object file */
        if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
                goto out;

        if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
                ret = stack_map_get_build_id_32(page_addr, build_id);
        else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
                ret = stack_map_get_build_id_64(page_addr, build_id);
out:
        put_page(page);
        return ret;
}

static void stack_map_get_build_id_offset(struct bpf_map *map,
                                          struct stack_map_bucket *bucket,
                                          u64 *ips, u32 trace_nr, bool user)
{
        int i;
        struct vm_area_struct *vma;
        struct bpf_stack_build_id *id_offs;

        bucket->nr = trace_nr;
        id_offs = (struct bpf_stack_build_id *)bucket->data;

        /*
         * We cannot do up_read() in nmi context, so build_id lookup is
         * only supported for non-nmi events. If at some point, it is
         * possible to run find_vma() without taking the semaphore, we
         * would like to allow build_id lookup in nmi context.
         *
         * Same fallback is used for kernel stack (!user) on a stackmap
         * with build_id.
         */
        if (!user || !current || !current->mm || in_nmi() ||
            down_read_trylock(&current->mm->mmap_sem) == 0) {
                /* cannot access current->mm, fall back to ips */
                for (i = 0; i < trace_nr; i++) {
                        id_offs[i].status = BPF_STACK_BUILD_ID_IP;
                        id_offs[i].ip = ips[i];
                }
                return;
        }

        for (i = 0; i < trace_nr; i++) {
                vma = find_vma(current->mm, ips[i]);
                if (!vma || stack_map_get_build_id(vma, id_offs[i].build_id)) {
                        /* per entry fall back to ips */
                        id_offs[i].status = BPF_STACK_BUILD_ID_IP;
                        id_offs[i].ip = ips[i];
                        continue;
                }
                id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + ips[i]
                        - vma->vm_start;
                id_offs[i].status = BPF_STACK_BUILD_ID_VALID;
        }
        up_read(&current->mm->mmap_sem);
}

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 / stack_map_data_size(map);
        /* 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;
        bool hash_matches;

        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]);

        hash_matches = bucket && bucket->hash == hash;
        /* fast cmp */
        if (hash_matches && flags & BPF_F_FAST_STACK_CMP)
                return id;

        if (stack_map_use_build_id(map)) {
                /* for build_id+offset, pop a bucket before slow cmp */
                new_bucket = (struct stack_map_bucket *)
                        pcpu_freelist_pop(&smap->freelist);
                if (unlikely(!new_bucket))
                        return -ENOMEM;
                stack_map_get_build_id_offset(map, new_bucket, ips,
                                              trace_nr, user);
                trace_len = trace_nr * sizeof(struct bpf_stack_build_id);
                if (hash_matches && bucket->nr == trace_nr &&
                    memcmp(bucket->data, new_bucket->data, trace_len) == 0) {
                        pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
                        return id;
                }
                if (bucket && !(flags & BPF_F_REUSE_STACKID)) {
                        pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
                        return -EEXIST;
                }
        } else {
                if (hash_matches && bucket->nr == trace_nr &&
                    memcmp(bucket->data, ips, trace_len) == 0)
                        return id;
                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->data, 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 * stack_map_data_size(map);
        memcpy(value, bucket->data, 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)
{
        struct bpf_stack_map *smap = container_of(map,
                                                  struct bpf_stack_map, map);
        u32 id;

        WARN_ON_ONCE(!rcu_read_lock_held());

        if (!key) {
                id = 0;
        } else {
                id = *(u32 *)key;
                if (id >= smap->n_buckets || !smap->buckets[id])
                        id = 0;
                else
                        id++;
        }

        while (id < smap->n_buckets && !smap->buckets[id])
                id++;

        if (id >= smap->n_buckets)
                return -ENOENT;

        *(u32 *)next_key = id;
        return 0;
}

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();
}

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,
};