bpf: introduce BPF_MAP_TYPE_STACK_TRACE

add new map type to store stack traces and corresponding helper
bpf_get_stackid(ctx, map, flags) - walk user or kernel stack and return id
@ctx: struct pt_regs*
@map: pointer to stack_trace map
@flags: bits 0-7 - numer of stack frames to skip
        bit 8 - collect user stack instead of kernel
        bit 9 - compare stacks by hash only
        bit 10 - if two different stacks hash into the same stackid
                 discard old
        other bits - reserved
Return: >= 0 stackid on success or negative error

stackid is a 32-bit integer handle that can be further combined with
other data (including other stackid) and used as a key into maps.

Userspace will access stackmap using standard lookup/delete syscall commands to
retrieve full stack trace for given stackid.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 237 insertions, 0 deletions

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
new file mode 100644
index 000000000000..8a60ee14a977
--- /dev/null
+++ b/kernel/bpf/stackmap.c
@@ -0,0 +1,237 @@
+/* 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/vmalloc.h>
+#include <linux/stacktrace.h>
+#include <linux/perf_event.h>
+
+struct stack_map_bucket {
+        struct rcu_head rcu;
+        u32 hash;
+        u32 nr;
+        u64 ip[];
+};
+
+struct bpf_stack_map {
+        struct bpf_map map;
+        u32 n_buckets;
+        struct stack_map_bucket __rcu *buckets[];
+};
+
+/* 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);
+
+        /* check sanity of attributes */
+        if (attr->max_entries == 0 || attr->key_size != 4 ||
+            value_size < 8 || value_size % 8 ||
+            value_size / 8 > PERF_MAX_STACK_DEPTH)
+                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 = kzalloc(cost, GFP_USER | __GFP_NOWARN);
+        if (!smap) {
+                smap = vzalloc(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->n_buckets = n_buckets;
+        smap->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
+
+        err = get_callchain_buffers();
+        if (err)
+                goto free_smap;
+
+        return &smap->map;
+
+free_smap:
+        kvfree(smap);
+        return ERR_PTR(err);
+}
+
+static u64 bpf_get_stackid(u64 r1, u64 r2, u64 flags, u64 r4, u64 r5)
+{
+        struct pt_regs *regs = (struct pt_regs *) (long) r1;
+        struct bpf_map *map = (struct bpf_map *) (long) r2;
+        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 <= PERF_MAX_STACK_DEPTH */
+        u32 init_nr = PERF_MAX_STACK_DEPTH - 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, 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 <= PERF_MAX_STACK_DEPTH, 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 = rcu_dereference(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 = kmalloc(sizeof(struct stack_map_bucket) + map->value_size,
+                             GFP_ATOMIC | __GFP_NOWARN);
+        if (unlikely(!new_bucket))
+                return -ENOMEM;
+
+        memcpy(new_bucket->ip, ips, trace_len);
+        memset(new_bucket->ip + trace_len / 8, 0, map->value_size - trace_len);
+        new_bucket->hash = hash;
+        new_bucket->nr = trace_nr;
+
+        old_bucket = xchg(&smap->buckets[id], new_bucket);
+        if (old_bucket)
+                kfree_rcu(old_bucket, rcu);
+        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 syscall or from eBPF program */
+static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
+{
+        struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
+        struct stack_map_bucket *bucket;
+        u32 id = *(u32 *)key;
+
+        if (unlikely(id >= smap->n_buckets))
+                return NULL;
+        bucket = rcu_dereference(smap->buckets[id]);
+        return bucket ? bucket->ip : NULL;
+}
+
+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) {
+                kfree_rcu(old_bucket, rcu);
+                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);
+        int i;
+
+        synchronize_rcu();
+
+        for (i = 0; i < smap->n_buckets; i++)
+                if (smap->buckets[i])
+                        kfree_rcu(smap->buckets[i], rcu);
+        kvfree(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);