[PATCH net-next 2/3] bpf: introduce BPF_MAP_TYPE_STACK_TRACE

Alexei Starovoitov
2016-02-18T03:59:31Z

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>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 21 +++++
kernel/bpf/Makefile | 3 +
kernel/bpf/stackmap.c | 237 +++++++++++++++++++++++++++++++++++++++++++++++
kernel/bpf/verifier.c | 6 +-
kernel/trace/bpf_trace.c | 2 +
6 files changed, 269 insertions(+), 1 deletion(-)
create mode 100644 kernel/bpf/stackmap.c

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 90ee6ab24bc5..0cadbb7456c0 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -237,6 +237,7 @@ extern const struct bpf_func_proto bpf_get_current_uid_gid_proto;
extern const struct bpf_func_proto bpf_get_current_comm_proto;
extern const struct bpf_func_proto bpf_skb_vlan_push_proto;
extern const struct bpf_func_proto bpf_skb_vlan_pop_proto;
+extern const struct bpf_func_proto bpf_get_stackid_proto;

/* Shared helpers among cBPF and eBPF. */
void bpf_user_rnd_init_once(void);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2ee0fde1bf96..d3e77da8e9e8 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -83,6 +83,7 @@ enum bpf_map_type {
BPF_MAP_TYPE_PERF_EVENT_ARRAY,
BPF_MAP_TYPE_PERCPU_HASH,
BPF_MAP_TYPE_PERCPU_ARRAY,
+ BPF_MAP_TYPE_STACK_TRACE,
};

enum bpf_prog_type {
@@ -272,6 +273,20 @@ enum bpf_func_id {
*/
BPF_FUNC_perf_event_output,
BPF_FUNC_skb_load_bytes,
+
+ /**
+ * 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
+ */
+ BPF_FUNC_get_stackid,
__BPF_FUNC_MAX_ID,
};

@@ -294,6 +309,12 @@ enum bpf_func_id {
/* BPF_FUNC_skb_set_tunnel_key and BPF_FUNC_skb_get_tunnel_key flags. */
#define BPF_F_TUNINFO_IPV6 (1ULL << 0)

+/* BPF_FUNC_get_stackid flags. */
+#define BPF_F_SKIP_FIELD_MASK 0xffULL
+#define BPF_F_USER_STACK (1ULL << 8)
+#define BPF_F_FAST_STACK_CMP (1ULL << 9)
+#define BPF_F_REUSE_STACKID (1ULL << 10)
+
/* user accessible mirror of in-kernel sk_buff.
* new fields can only be added to the end of this structure
*/
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 13272582eee0..8a932d079c24 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -2,3 +2,6 @@ obj-y := core.o

obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o
obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o
+ifeq ($(CONFIG_PERF_EVENTS),y)
+obj-$(CONFIG_BPF_SYSCALL) += stackmap.o
+endif
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);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d1d3e8f57de9..42ba4ccc020b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -246,6 +246,7 @@ static const struct {
{BPF_MAP_TYPE_PROG_ARRAY, BPF_FUNC_tail_call},
{BPF_MAP_TYPE_PERF_EVENT_ARRAY, BPF_FUNC_perf_event_read},
{BPF_MAP_TYPE_PERF_EVENT_ARRAY, BPF_FUNC_perf_event_output},
+ {BPF_MAP_TYPE_STACK_TRACE, BPF_FUNC_get_stackid},
};

static void print_verifier_state(struct verifier_env *env)
@@ -911,8 +912,11 @@ static int check_map_func_compatibility(struct bpf_map *map, int func_id)
* don't allow any other map type to be passed into
* the special func;
*/
- if (bool_func && bool_map != bool_func)
+ if (bool_func && bool_map != bool_func) {
+ verbose("cannot pass map_type %d into func %d\n",
+ map->map_type, func_id);
return -EINVAL;
+ }
}

return 0;
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 326a75e884db..4b8caa392b86 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -299,6 +299,8 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
return &bpf_perf_event_read_proto;
case BPF_FUNC_perf_event_output:
return &bpf_perf_event_output_proto;
+ case BPF_FUNC_get_stackid:
+ return &bpf_get_stackid_proto;
default:
return NULL;
}
--
2.4.6