Merge branch 'queue_stack_maps'

Mauricio Vasquez says:

====================
In some applications this is needed have a pool of free elements, for
example the list of free L4 ports in a SNAT.  None of the current maps allow
to do it as it is not possible to get any element without having they key
it is associated to, even if it were possible, the lack of locking mecanishms in
eBPF would do it almost impossible to be implemented without data races.

This patchset implements two new kind of eBPF maps: queue and stack.
Those maps provide to eBPF programs the peek, push and pop operations, and for
userspace applications a new bpf_map_lookup_and_delete_elem() is added.
Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>

v2 -> v3:
 - Remove "almost dead code" in syscall.c
 - Remove unnecessary copy_from_user in bpf_map_lookup_and_delete_elem
 - Rebase

v1 -> v2:
 - Put ARG_PTR_TO_UNINIT_MAP_VALUE logic into a separated patch
 - Fix missing __this_cpu_dec & preempt_enable calls in kernel/bpf/syscall.c

RFC v4 -> v1:
 - Remove roundup to power of 2 in memory allocation
 - Remove count and use a free slot to check if queue/stack is empty
 - Use if + assigment for wrapping indexes
 - Fix some minor style issues
 - Squash two patches together

RFC v3 -> RFC v4:
 - Revert renaming of kernel/bpf/stackmap.c
 - Remove restriction on value size
 - Remove len arguments from peek/pop helpers
 - Add new ARG_PTR_TO_UNINIT_MAP_VALUE

RFC v2 -> RFC v3:
 - Return elements by value instead that by reference
 - Implement queue/stack base on array and head + tail indexes
 - Rename stack trace related files to avoid confusion and conflicts

RFC v1 -> RFC v2:
 - Create two separate maps instead of single one + flags
 - Implement bpf_map_lookup_and_delete syscall
 - Support peek operation
 - Define replacement policy through flags in the update() method
 - Add eBPF side tests
====================
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf.h

@@ -39,6 +39,9 @@ struct bpf_map_ops {
 	void *(*map_lookup_elem)(struct bpf_map *map, void *key);
 	int (*map_update_elem)(struct bpf_map *map, void *key, void *value, u64 flags);
 	int (*map_delete_elem)(struct bpf_map *map, void *key);
+	int (*map_push_elem)(struct bpf_map *map, void *value, u64 flags);
+	int (*map_pop_elem)(struct bpf_map *map, void *value);
+	int (*map_peek_elem)(struct bpf_map *map, void *value);
 
 	/* funcs called by prog_array and perf_event_array map */
 	void *(*map_fd_get_ptr)(struct bpf_map *map, struct file *map_file,
@@ -138,6 +141,7 @@ enum bpf_arg_type {
 	ARG_CONST_MAP_PTR,	/* const argument used as pointer to bpf_map */
 	ARG_PTR_TO_MAP_KEY,	/* pointer to stack used as map key */
 	ARG_PTR_TO_MAP_VALUE,	/* pointer to stack used as map value */
+	ARG_PTR_TO_UNINIT_MAP_VALUE,	/* pointer to valid memory used to store a map value */
 
 	/* the following constraints used to prototype bpf_memcmp() and other
 	 * functions that access data on eBPF program stack
@@ -810,6 +814,9 @@ static inline int bpf_fd_reuseport_array_update_elem(struct bpf_map *map,
 extern const struct bpf_func_proto bpf_map_lookup_elem_proto;
 extern const struct bpf_func_proto bpf_map_update_elem_proto;
 extern const struct bpf_func_proto bpf_map_delete_elem_proto;
+extern const struct bpf_func_proto bpf_map_push_elem_proto;
+extern const struct bpf_func_proto bpf_map_pop_elem_proto;
+extern const struct bpf_func_proto bpf_map_peek_elem_proto;
 
 extern const struct bpf_func_proto bpf_get_prandom_u32_proto;
 extern const struct bpf_func_proto bpf_get_smp_processor_id_proto;

include/linux/bpf_types.h

@@ -51,7 +51,7 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_LRU_HASH, htab_lru_map_ops)
 BPF_MAP_TYPE(BPF_MAP_TYPE_LRU_PERCPU_HASH, htab_lru_percpu_map_ops)
 BPF_MAP_TYPE(BPF_MAP_TYPE_LPM_TRIE, trie_map_ops)
 #ifdef CONFIG_PERF_EVENTS
-BPF_MAP_TYPE(BPF_MAP_TYPE_STACK_TRACE, stack_map_ops)
+BPF_MAP_TYPE(BPF_MAP_TYPE_STACK_TRACE, stack_trace_map_ops)
 #endif
 BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY_OF_MAPS, array_of_maps_map_ops)
 BPF_MAP_TYPE(BPF_MAP_TYPE_HASH_OF_MAPS, htab_of_maps_map_ops)
@@ -69,3 +69,5 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_XSKMAP, xsk_map_ops)
 BPF_MAP_TYPE(BPF_MAP_TYPE_REUSEPORT_SOCKARRAY, reuseport_array_ops)
 #endif
 #endif
+BPF_MAP_TYPE(BPF_MAP_TYPE_QUEUE, queue_map_ops)
+BPF_MAP_TYPE(BPF_MAP_TYPE_STACK, stack_map_ops)

include/uapi/linux/bpf.h

@@ -103,6 +103,7 @@ enum bpf_cmd {
 	BPF_BTF_LOAD,
 	BPF_BTF_GET_FD_BY_ID,
 	BPF_TASK_FD_QUERY,
+	BPF_MAP_LOOKUP_AND_DELETE_ELEM,
 };
 
 enum bpf_map_type {
@@ -128,6 +129,8 @@ enum bpf_map_type {
 	BPF_MAP_TYPE_CGROUP_STORAGE,
 	BPF_MAP_TYPE_REUSEPORT_SOCKARRAY,
 	BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE,
+	BPF_MAP_TYPE_QUEUE,
+	BPF_MAP_TYPE_STACK,
 };
 
 enum bpf_prog_type {
@@ -462,6 +465,28 @@ union bpf_attr {
  * 	Return
  * 		0 on success, or a negative error in case of failure.
  *
+ * int bpf_map_push_elem(struct bpf_map *map, const void *value, u64 flags)
+ * 	Description
+ * 		Push an element *value* in *map*. *flags* is one of:
+ *
+ * 		**BPF_EXIST**
+ * 		If the queue/stack is full, the oldest element is removed to
+ * 		make room for this.
+ * 	Return
+ * 		0 on success, or a negative error in case of failure.
+ *
+ * int bpf_map_pop_elem(struct bpf_map *map, void *value)
+ * 	Description
+ * 		Pop an element from *map*.
+ * Return
+ * 		0 on success, or a negative error in case of failure.
+ *
+ * int bpf_map_peek_elem(struct bpf_map *map, void *value)
+ * 	Description
+ * 		Get an element from *map* without removing it.
+ * Return
+ * 		0 on success, or a negative error in case of failure.
+ *
  * int bpf_probe_read(void *dst, u32 size, const void *src)
  * 	Description
  * 		For tracing programs, safely attempt to read *size* bytes from
@@ -2303,7 +2328,10 @@ union bpf_attr {
 	FN(skb_ancestor_cgroup_id),	\
 	FN(sk_lookup_tcp),		\
 	FN(sk_lookup_udp),		\
-	FN(sk_release),
+	FN(sk_release),			\
+	FN(map_push_elem),		\
+	FN(map_pop_elem),		\
+	FN(map_peek_elem),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call

kernel/bpf/Makefile

@@ -3,7 +3,7 @@ obj-y := core.o
 
 obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o
-obj-$(CONFIG_BPF_SYSCALL) += local_storage.o
+obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o
 obj-$(CONFIG_BPF_SYSCALL) += disasm.o
 obj-$(CONFIG_BPF_SYSCALL) += btf.o
 ifeq ($(CONFIG_NET),y)

kernel/bpf/core.c

@@ -1783,6 +1783,9 @@ BPF_CALL_0(bpf_user_rnd_u32)
 const struct bpf_func_proto bpf_map_lookup_elem_proto __weak;
 const struct bpf_func_proto bpf_map_update_elem_proto __weak;
 const struct bpf_func_proto bpf_map_delete_elem_proto __weak;
+const struct bpf_func_proto bpf_map_push_elem_proto __weak;
+const struct bpf_func_proto bpf_map_pop_elem_proto __weak;
+const struct bpf_func_proto bpf_map_peek_elem_proto __weak;
 
 const struct bpf_func_proto bpf_get_prandom_u32_proto __weak;
 const struct bpf_func_proto bpf_get_smp_processor_id_proto __weak;

kernel/bpf/helpers.c

@@ -76,6 +76,49 @@ const struct bpf_func_proto bpf_map_delete_elem_proto = {
 	.arg2_type	= ARG_PTR_TO_MAP_KEY,
 };
 
+BPF_CALL_3(bpf_map_push_elem, struct bpf_map *, map, void *, value, u64, flags)
+{
+	return map->ops->map_push_elem(map, value, flags);
+}
+
+const struct bpf_func_proto bpf_map_push_elem_proto = {
+	.func		= bpf_map_push_elem,
+	.gpl_only	= false,
+	.pkt_access	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_CONST_MAP_PTR,
+	.arg2_type	= ARG_PTR_TO_MAP_VALUE,
+	.arg3_type	= ARG_ANYTHING,
+};
+
+BPF_CALL_2(bpf_map_pop_elem, struct bpf_map *, map, void *, value)
+{
+	return map->ops->map_pop_elem(map, value);
+}
+
+const struct bpf_func_proto bpf_map_pop_elem_proto = {
+	.func		= bpf_map_pop_elem,
+	.gpl_only	= false,
+	.pkt_access	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_CONST_MAP_PTR,
+	.arg2_type	= ARG_PTR_TO_UNINIT_MAP_VALUE,
+};
+
+BPF_CALL_2(bpf_map_peek_elem, struct bpf_map *, map, void *, value)
+{
+	return map->ops->map_peek_elem(map, value);
+}
+
+const struct bpf_func_proto bpf_map_peek_elem_proto = {
+	.func		= bpf_map_pop_elem,
+	.gpl_only	= false,
+	.pkt_access	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_CONST_MAP_PTR,
+	.arg2_type	= ARG_PTR_TO_UNINIT_MAP_VALUE,
+};
+
 const struct bpf_func_proto bpf_get_prandom_u32_proto = {
 	.func		= bpf_user_rnd_u32,
 	.gpl_only	= false,

kernel/bpf/queue_stack_maps.c

+// 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 "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)
+{
+	/* check sanity of attributes */
+	if (attr->max_entries == 0 || attr->key_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;
+	u32 size, value_size;
+	u64 queue_size, cost;
+
+	size = attr->max_entries + 1;
+	value_size = attr->value_size;
+
+	queue_size = sizeof(*qs) + (u64) value_size * size;
+
+	cost = queue_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)) {
+		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)) {
+		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,
+};

kernel/bpf/stackmap.c

@@ -600,7 +600,7 @@ static void stack_map_free(struct bpf_map *map)
 	put_callchain_buffers();
 }
 
-const struct bpf_map_ops stack_map_ops = {
+const struct bpf_map_ops stack_trace_map_ops = {
 	.map_alloc = stack_map_alloc,
 	.map_free = stack_map_free,
 	.map_get_next_key = stack_map_get_next_key,

kernel/bpf/syscall.c

@@ -651,6 +651,17 @@ int __weak bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
 	return -ENOTSUPP;
 }
 
+static void *__bpf_copy_key(void __user *ukey, u64 key_size)
+{
+	if (key_size)
+		return memdup_user(ukey, key_size);
+
+	if (ukey)
+		return ERR_PTR(-EINVAL);
+
+	return NULL;
+}
+
 /* last field in 'union bpf_attr' used by this command */
 #define BPF_MAP_LOOKUP_ELEM_LAST_FIELD value
 
@@ -678,7 +689,7 @@ static int map_lookup_elem(union bpf_attr *attr)
 		goto err_put;
 	}
 
-	key = memdup_user(ukey, map->key_size);
+	key = __bpf_copy_key(ukey, map->key_size);
 	if (IS_ERR(key)) {
 		err = PTR_ERR(key);
 		goto err_put;
@@ -716,6 +727,9 @@ static int map_lookup_elem(union bpf_attr *attr)
 		err = bpf_fd_htab_map_lookup_elem(map, key, value);
 	} else if (map->map_type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY) {
 		err = bpf_fd_reuseport_array_lookup_elem(map, key, value);
+	} else if (map->map_type == BPF_MAP_TYPE_QUEUE ||
+		   map->map_type == BPF_MAP_TYPE_STACK) {
+		err = map->ops->map_peek_elem(map, value);
 	} else {
 		rcu_read_lock();
 		ptr = map->ops->map_lookup_elem(map, key);
@@ -785,7 +799,7 @@ static int map_update_elem(union bpf_attr *attr)
 		goto err_put;
 	}
 
-	key = memdup_user(ukey, map->key_size);
+	key = __bpf_copy_key(ukey, map->key_size);
 	if (IS_ERR(key)) {
 		err = PTR_ERR(key);
 		goto err_put;
@@ -846,6 +860,9 @@ static int map_update_elem(union bpf_attr *attr)
 		/* rcu_read_lock() is not needed */
 		err = bpf_fd_reuseport_array_update_elem(map, key, value,
 							 attr->flags);
+	} else if (map->map_type == BPF_MAP_TYPE_QUEUE ||
+		   map->map_type == BPF_MAP_TYPE_STACK) {
+		err = map->ops->map_push_elem(map, value, attr->flags);
 	} else {
 		rcu_read_lock();
 		err = map->ops->map_update_elem(map, key, value, attr->flags);
@@ -888,7 +905,7 @@ static int map_delete_elem(union bpf_attr *attr)
 		goto err_put;
 	}
 
-	key = memdup_user(ukey, map->key_size);
+	key = __bpf_copy_key(ukey, map->key_size);
 	if (IS_ERR(key)) {
 		err = PTR_ERR(key);
 		goto err_put;
@@ -941,7 +958,7 @@ static int map_get_next_key(union bpf_attr *attr)
 	}
 
 	if (ukey) {
-		key = memdup_user(ukey, map->key_size);
+		key = __bpf_copy_key(ukey, map->key_size);
 		if (IS_ERR(key)) {
 			err = PTR_ERR(key);
 			goto err_put;
@@ -982,6 +999,69 @@ static int map_get_next_key(union bpf_attr *attr)
 	return err;
 }
 
+#define BPF_MAP_LOOKUP_AND_DELETE_ELEM_LAST_FIELD value
+
+static int map_lookup_and_delete_elem(union bpf_attr *attr)
+{
+	void __user *ukey = u64_to_user_ptr(attr->key);
+	void __user *uvalue = u64_to_user_ptr(attr->value);
+	int ufd = attr->map_fd;
+	struct bpf_map *map;
+	void *key, *value, *ptr;
+	u32 value_size;
+	struct fd f;
+	int err;
+
+	if (CHECK_ATTR(BPF_MAP_LOOKUP_AND_DELETE_ELEM))
+		return -EINVAL;
+
+	f = fdget(ufd);
+	map = __bpf_map_get(f);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
+
+	if (!(f.file->f_mode & FMODE_CAN_WRITE)) {
+		err = -EPERM;
+		goto err_put;
+	}
+
+	key = __bpf_copy_key(ukey, map->key_size);
+	if (IS_ERR(key)) {
+		err = PTR_ERR(key);
+		goto err_put;
+	}
+
+	value_size = map->value_size;
+
+	err = -ENOMEM;
+	value = kmalloc(value_size, GFP_USER | __GFP_NOWARN);
+	if (!value)
+		goto free_key;
+
+	if (map->map_type == BPF_MAP_TYPE_QUEUE ||
+	    map->map_type == BPF_MAP_TYPE_STACK) {
+		err = map->ops->map_pop_elem(map, value);
+	} else {
+		err = -ENOTSUPP;
+	}
+
+	if (err)
+		goto free_value;
+
+	if (copy_to_user(uvalue, value, value_size) != 0)
+		goto free_value;
+
+	err = 0;
+
+free_value:
+	kfree(value);
+free_key:
+	kfree(key);
+err_put:
+	fdput(f);
+	return err;
+}
+
 static const struct bpf_prog_ops * const bpf_prog_types[] = {
 #define BPF_PROG_TYPE(_id, _name) \
 	[_id] = & _name ## _prog_ops,
@@ -2455,6 +2535,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
 	case BPF_TASK_FD_QUERY:
 		err = bpf_task_fd_query(&attr, uattr);
 		break;
+	case BPF_MAP_LOOKUP_AND_DELETE_ELEM:
+		err = map_lookup_and_delete_elem(&attr);
+		break;
 	default:
 		err = -EINVAL;
 		break;

kernel/bpf/verifier.c

@@ -2117,7 +2117,8 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
 	}
 
 	if (arg_type == ARG_PTR_TO_MAP_KEY ||
-	    arg_type == ARG_PTR_TO_MAP_VALUE) {
+	    arg_type == ARG_PTR_TO_MAP_VALUE ||
+	    arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE) {
 		expected_type = PTR_TO_STACK;
 		if (!type_is_pkt_pointer(type) && type != PTR_TO_MAP_VALUE &&
 		    type != expected_type)
@@ -2187,7 +2188,8 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
 		err = check_helper_mem_access(env, regno,
 					      meta->map_ptr->key_size, false,
 					      NULL);
-	} else if (arg_type == ARG_PTR_TO_MAP_VALUE) {
+	} else if (arg_type == ARG_PTR_TO_MAP_VALUE ||
+		   arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE) {
 		/* bpf_map_xxx(..., map_ptr, ..., value) call:
 		 * check [value, value + map->value_size) validity
 		 */
@@ -2196,9 +2198,10 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
 			verbose(env, "invalid map_ptr to access map->value\n");
 			return -EACCES;
 		}
+		meta->raw_mode = (arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE);
 		err = check_helper_mem_access(env, regno,
 					      meta->map_ptr->value_size, false,
-					      NULL);
+					      meta);
 	} else if (arg_type_is_mem_size(arg_type)) {
 		bool zero_size_allowed = (arg_type == ARG_CONST_SIZE_OR_ZERO);
 
@@ -2321,6 +2324,13 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
 		if (func_id != BPF_FUNC_sk_select_reuseport)
 			goto error;
 		break;
+	case BPF_MAP_TYPE_QUEUE:
+	case BPF_MAP_TYPE_STACK:
+		if (func_id != BPF_FUNC_map_peek_elem &&
+		    func_id != BPF_FUNC_map_pop_elem &&
+		    func_id != BPF_FUNC_map_push_elem)
+			goto error;
+		break;
 	default:
 		break;
 	}
@@ -2377,6 +2387,13 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
 		if (map->map_type != BPF_MAP_TYPE_REUSEPORT_SOCKARRAY)
 			goto error;
 		break;
+	case BPF_FUNC_map_peek_elem:
+	case BPF_FUNC_map_pop_elem:
+	case BPF_FUNC_map_push_elem:
+		if (map->map_type != BPF_MAP_TYPE_QUEUE &&
+		    map->map_type != BPF_MAP_TYPE_STACK)
+			goto error;
+		break;
 	default:
 		break;
 	}
@@ -2672,7 +2689,10 @@ record_func_map(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
 	if (func_id != BPF_FUNC_tail_call &&
 	    func_id != BPF_FUNC_map_lookup_elem &&
 	    func_id != BPF_FUNC_map_update_elem &&
-	    func_id != BPF_FUNC_map_delete_elem)
+	    func_id != BPF_FUNC_map_delete_elem &&
+	    func_id != BPF_FUNC_map_push_elem &&
+	    func_id != BPF_FUNC_map_pop_elem &&
+	    func_id != BPF_FUNC_map_peek_elem)
 		return 0;
 
 	if (meta->map_ptr == NULL) {

net/core/filter.c

@@ -4876,6 +4876,12 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 		return &bpf_map_update_elem_proto;
 	case BPF_FUNC_map_delete_elem:
 		return &bpf_map_delete_elem_proto;
+	case BPF_FUNC_map_push_elem:
+		return &bpf_map_push_elem_proto;
+	case BPF_FUNC_map_pop_elem:
+		return &bpf_map_pop_elem_proto;
+	case BPF_FUNC_map_peek_elem:
+		return &bpf_map_peek_elem_proto;
 	case BPF_FUNC_get_prandom_u32:
 		return &bpf_get_prandom_u32_proto;
 	case BPF_FUNC_get_smp_processor_id:

tools/include/uapi/linux/bpf.h

@@ -103,6 +103,7 @@ enum bpf_cmd {
 	BPF_BTF_LOAD,
 	BPF_BTF_GET_FD_BY_ID,
 	BPF_TASK_FD_QUERY,
+	BPF_MAP_LOOKUP_AND_DELETE_ELEM,
 };
 
 enum bpf_map_type {
@@ -128,6 +129,8 @@ enum bpf_map_type {
 	BPF_MAP_TYPE_CGROUP_STORAGE,
 	BPF_MAP_TYPE_REUSEPORT_SOCKARRAY,
 	BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE,
+	BPF_MAP_TYPE_QUEUE,
+	BPF_MAP_TYPE_STACK,
 };
 
 enum bpf_prog_type {
@@ -462,6 +465,28 @@ union bpf_attr {
  * 	Return
  * 		0 on success, or a negative error in case of failure.
  *
+ * int bpf_map_push_elem(struct bpf_map *map, const void *value, u64 flags)
+ * 	Description
+ * 		Push an element *value* in *map*. *flags* is one of:
+ *
+ * 		**BPF_EXIST**
+ * 		If the queue/stack is full, the oldest element is removed to
+ * 		make room for this.
+ * 	Return
+ * 		0 on success, or a negative error in case of failure.
+ *
+ * int bpf_map_pop_elem(struct bpf_map *map, void *value)
+ * 	Description
+ * 		Pop an element from *map*.
+ * Return
+ * 		0 on success, or a negative error in case of failure.
+ *
+ * int bpf_map_peek_elem(struct bpf_map *map, void *value)
+ * 	Description
+ * 		Get an element from *map* without removing it.
+ * Return
+ * 		0 on success, or a negative error in case of failure.
+ *
  * int bpf_probe_read(void *dst, u32 size, const void *src)
  * 	Description
  * 		For tracing programs, safely attempt to read *size* bytes from
@@ -2303,7 +2328,10 @@ union bpf_attr {
 	FN(skb_ancestor_cgroup_id),	\
 	FN(sk_lookup_tcp),		\
 	FN(sk_lookup_udp),		\
-	FN(sk_release),
+	FN(sk_release),			\
+	FN(map_push_elem),		\
+	FN(map_pop_elem),		\
+	FN(map_peek_elem),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call

tools/lib/bpf/bpf.c

@@ -278,6 +278,18 @@ int bpf_map_lookup_elem(int fd, const void *key, void *value)
 	return sys_bpf(BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr));
 }
 
+int bpf_map_lookup_and_delete_elem(int fd, const void *key, void *value)
+{
+	union bpf_attr attr;
+
+	bzero(&attr, sizeof(attr));
+	attr.map_fd = fd;
+	attr.key = ptr_to_u64(key);
+	attr.value = ptr_to_u64(value);
+
+	return sys_bpf(BPF_MAP_LOOKUP_AND_DELETE_ELEM, &attr, sizeof(attr));
+}
+
 int bpf_map_delete_elem(int fd, const void *key)
 {
 	union bpf_attr attr;

tools/lib/bpf/bpf.h

@@ -99,6 +99,8 @@ LIBBPF_API int bpf_map_update_elem(int fd, const void *key, const void *value,
 				   __u64 flags);
 
 LIBBPF_API int bpf_map_lookup_elem(int fd, const void *key, void *value);
+LIBBPF_API int bpf_map_lookup_and_delete_elem(int fd, const void *key,
+					      void *value);
 LIBBPF_API int bpf_map_delete_elem(int fd, const void *key);
 LIBBPF_API int bpf_map_get_next_key(int fd, const void *key, void *next_key);
 LIBBPF_API int bpf_obj_pin(int fd, const char *pathname);

tools/testing/selftests/bpf/Makefile

@@ -37,7 +37,7 @@ TEST_GEN_FILES = test_pkt_access.o test_xdp.o test_l4lb.o test_tcp_estats.o test
 	test_lwt_seg6local.o sendmsg4_prog.o sendmsg6_prog.o test_lirc_mode2_kern.o \
 	get_cgroup_id_kern.o socket_cookie_prog.o test_select_reuseport_kern.o \
 	test_skb_cgroup_id_kern.o bpf_flow.o netcnt_prog.o \
-	test_sk_lookup_kern.o test_xdp_vlan.o
+	test_sk_lookup_kern.o test_xdp_vlan.o test_queue_map.o test_stack_map.o
 
 # Order correspond to 'make run_tests' order
 TEST_PROGS := test_kmod.sh \
@@ -118,6 +118,9 @@ CLANG_FLAGS = -I. -I./include/uapi -I../../../include/uapi \
 $(OUTPUT)/test_l4lb_noinline.o: CLANG_FLAGS += -fno-inline
 $(OUTPUT)/test_xdp_noinline.o: CLANG_FLAGS += -fno-inline
 
+$(OUTPUT)/test_queue_map.o: test_queue_stack_map.h
+$(OUTPUT)/test_stack_map.o: test_queue_stack_map.h
+
 BTF_LLC_PROBE := $(shell $(LLC) -march=bpf -mattr=help 2>&1 | grep dwarfris)
 BTF_PAHOLE_PROBE := $(shell $(BTF_PAHOLE) --help 2>&1 | grep BTF)
 BTF_OBJCOPY_PROBE := $(shell $(LLVM_OBJCOPY) --help 2>&1 | grep -i 'usage.*llvm')

tools/testing/selftests/bpf/bpf_helpers.h

@@ -16,6 +16,13 @@ static int (*bpf_map_update_elem)(void *map, void *key, void *value,
 	(void *) BPF_FUNC_map_update_elem;
 static int (*bpf_map_delete_elem)(void *map, void *key) =
 	(void *) BPF_FUNC_map_delete_elem;
+static int (*bpf_map_push_elem)(void *map, void *value,
+				unsigned long long flags) =
+	(void *) BPF_FUNC_map_push_elem;
+static int (*bpf_map_pop_elem)(void *map, void *value) =
+	(void *) BPF_FUNC_map_pop_elem;
+static int (*bpf_map_peek_elem)(void *map, void *value) =
+	(void *) BPF_FUNC_map_peek_elem;
 static int (*bpf_probe_read)(void *dst, int size, void *unsafe_ptr) =
 	(void *) BPF_FUNC_probe_read;
 static unsigned long long (*bpf_ktime_get_ns)(void) =

tools/testing/selftests/bpf/test_maps.c

@@ -15,6 +15,7 @@
 #include <string.h>
 #include <assert.h>
 #include <stdlib.h>
+#include <time.h>
 
 #include <sys/wait.h>
 #include <sys/socket.h>
@@ -471,6 +472,122 @@ static void test_devmap(int task, void *data)
 	close(fd);
 }
 
+static void test_queuemap(int task, void *data)
+{
+	const int MAP_SIZE = 32;
+	__u32 vals[MAP_SIZE + MAP_SIZE/2], val;
+	int fd, i;
+
+	/* Fill test values to be used */
+	for (i = 0; i < MAP_SIZE + MAP_SIZE/2; i++)
+		vals[i] = rand();
+
+	/* Invalid key size */
+	fd = bpf_create_map(BPF_MAP_TYPE_QUEUE, 4, sizeof(val), MAP_SIZE,
+			    map_flags);
+	assert(fd < 0 && errno == EINVAL);
+
+	fd = bpf_create_map(BPF_MAP_TYPE_QUEUE, 0, sizeof(val), MAP_SIZE,
+			    map_flags);
+	/* Queue map does not support BPF_F_NO_PREALLOC */
+	if (map_flags & BPF_F_NO_PREALLOC) {
+		assert(fd < 0 && errno == EINVAL);
+		return;
+	}
+	if (fd < 0) {
+		printf("Failed to create queuemap '%s'!\n", strerror(errno));
+		exit(1);
+	}
+
+	/* Push MAP_SIZE elements */
+	for (i = 0; i < MAP_SIZE; i++)
+		assert(bpf_map_update_elem(fd, NULL, &vals[i], 0) == 0);
+
+	/* Check that element cannot be pushed due to max_entries limit */
+	assert(bpf_map_update_elem(fd, NULL, &val, 0) == -1 &&
+	       errno == E2BIG);
+
+	/* Peek element */
+	assert(bpf_map_lookup_elem(fd, NULL, &val) == 0 && val == vals[0]);
+
+	/* Replace half elements */
+	for (i = MAP_SIZE; i < MAP_SIZE + MAP_SIZE/2; i++)
+		assert(bpf_map_update_elem(fd, NULL, &vals[i], BPF_EXIST) == 0);
+
+	/* Pop all elements */
+	for (i = MAP_SIZE/2; i < MAP_SIZE + MAP_SIZE/2; i++)
+		assert(bpf_map_lookup_and_delete_elem(fd, NULL, &val) == 0 &&
+		       val == vals[i]);
+
+	/* Check that there are not elements left */
+	assert(bpf_map_lookup_and_delete_elem(fd, NULL, &val) == -1 &&
+	       errno == ENOENT);
+
+	/* Check that non supported functions set errno to EINVAL */
+	assert(bpf_map_delete_elem(fd, NULL) == -1 && errno == EINVAL);
+	assert(bpf_map_get_next_key(fd, NULL, NULL) == -1 && errno == EINVAL);
+
+	close(fd);
+}
+
+static void test_stackmap(int task, void *data)
+{
+	const int MAP_SIZE = 32;
+	__u32 vals[MAP_SIZE + MAP_SIZE/2], val;
+	int fd, i;
+
+	/* Fill test values to be used */
+	for (i = 0; i < MAP_SIZE + MAP_SIZE/2; i++)
+		vals[i] = rand();
+
+	/* Invalid key size */
+	fd = bpf_create_map(BPF_MAP_TYPE_STACK, 4, sizeof(val), MAP_SIZE,
+			    map_flags);
+	assert(fd < 0 && errno == EINVAL);
+
+	fd = bpf_create_map(BPF_MAP_TYPE_STACK, 0, sizeof(val), MAP_SIZE,
+			    map_flags);
+	/* Stack map does not support BPF_F_NO_PREALLOC */
+	if (map_flags & BPF_F_NO_PREALLOC) {
+		assert(fd < 0 && errno == EINVAL);
+		return;
+	}
+	if (fd < 0) {
+		printf("Failed to create stackmap '%s'!\n", strerror(errno));
+		exit(1);
+	}
+
+	/* Push MAP_SIZE elements */
+	for (i = 0; i < MAP_SIZE; i++)
+		assert(bpf_map_update_elem(fd, NULL, &vals[i], 0) == 0);
+
+	/* Check that element cannot be pushed due to max_entries limit */
+	assert(bpf_map_update_elem(fd, NULL, &val, 0) == -1 &&
+	       errno == E2BIG);
+
+	/* Peek element */
+	assert(bpf_map_lookup_elem(fd, NULL, &val) == 0 && val == vals[i - 1]);
+
+	/* Replace half elements */
+	for (i = MAP_SIZE; i < MAP_SIZE + MAP_SIZE/2; i++)
+		assert(bpf_map_update_elem(fd, NULL, &vals[i], BPF_EXIST) == 0);
+
+	/* Pop all elements */
+	for (i = MAP_SIZE + MAP_SIZE/2 - 1; i >= MAP_SIZE/2; i--)
+		assert(bpf_map_lookup_and_delete_elem(fd, NULL, &val) == 0 &&
+		       val == vals[i]);
+
+	/* Check that there are not elements left */
+	assert(bpf_map_lookup_and_delete_elem(fd, NULL, &val) == -1 &&
+	       errno == ENOENT);
+
+	/* Check that non supported functions set errno to EINVAL */
+	assert(bpf_map_delete_elem(fd, NULL) == -1 && errno == EINVAL);
+	assert(bpf_map_get_next_key(fd, NULL, NULL) == -1 && errno == EINVAL);
+
+	close(fd);
+}
+
 #include <sys/socket.h>
 #include <sys/ioctl.h>
 #include <arpa/inet.h>
@@ -1434,10 +1551,15 @@ static void run_all_tests(void)
 	test_map_wronly();
 
 	test_reuseport_array();
+
+	test_queuemap(0, NULL);
+	test_stackmap(0, NULL);
 }
 
 int main(void)
 {
+	srand(time(NULL));
+
 	map_flags = 0;
 	run_all_tests();
 

tools/testing/selftests/bpf/test_progs.c

@@ -1735,8 +1735,105 @@ static void test_reference_tracking()
 	bpf_object__close(obj);
 }
 
+enum {
+	QUEUE,
+	STACK,
+};
+
+static void test_queue_stack_map(int type)
+{
+	const int MAP_SIZE = 32;
+	__u32 vals[MAP_SIZE], duration, retval, size, val;
+	int i, err, prog_fd, map_in_fd, map_out_fd;
+	char file[32], buf[128];
+	struct bpf_object *obj;
+	struct iphdr *iph = (void *)buf + sizeof(struct ethhdr);
+
+	/* Fill test values to be used */
+	for (i = 0; i < MAP_SIZE; i++)
+		vals[i] = rand();
+
+	if (type == QUEUE)
+		strncpy(file, "./test_queue_map.o", sizeof(file));
+	else if (type == STACK)
+		strncpy(file, "./test_stack_map.o", sizeof(file));
+	else
+		return;
+
+	err = bpf_prog_load(file, BPF_PROG_TYPE_SCHED_CLS, &obj, &prog_fd);
+	if (err) {
+		error_cnt++;
+		return;
+	}
+
+	map_in_fd = bpf_find_map(__func__, obj, "map_in");
+	if (map_in_fd < 0)
+		goto out;
+
+	map_out_fd = bpf_find_map(__func__, obj, "map_out");
+	if (map_out_fd < 0)
+		goto out;
+
+	/* Push 32 elements to the input map */
+	for (i = 0; i < MAP_SIZE; i++) {
+		err = bpf_map_update_elem(map_in_fd, NULL, &vals[i], 0);
+		if (err) {
+			error_cnt++;
+			goto out;
+		}
+	}
+
+	/* The eBPF program pushes iph.saddr in the output map,
+	 * pops the input map and saves this value in iph.daddr
+	 */
+	for (i = 0; i < MAP_SIZE; i++) {
+		if (type == QUEUE) {
+			val = vals[i];
+			pkt_v4.iph.saddr = vals[i] * 5;
+		} else if (type == STACK) {
+			val = vals[MAP_SIZE - 1 - i];
+			pkt_v4.iph.saddr = vals[MAP_SIZE - 1 - i] * 5;
+		}
+
+		err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+					buf, &size, &retval, &duration);
+		if (err || retval || size != sizeof(pkt_v4) ||
+		    iph->daddr != val)
+			break;
+	}
+
+	CHECK(err || retval || size != sizeof(pkt_v4) || iph->daddr != val,
+	      "bpf_map_pop_elem",
+	      "err %d errno %d retval %d size %d iph->daddr %u\n",
+	      err, errno, retval, size, iph->daddr);
+
+	/* Queue is empty, program should return TC_ACT_SHOT */
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				buf, &size, &retval, &duration);
+	CHECK(err || retval != 2 /* TC_ACT_SHOT */|| size != sizeof(pkt_v4),
+	      "check-queue-stack-map-empty",
+	      "err %d errno %d retval %d size %d\n",
+	      err, errno, retval, size);
+
+	/* Check that the program pushed elements correctly */
+	for (i = 0; i < MAP_SIZE; i++) {
+		err = bpf_map_lookup_and_delete_elem(map_out_fd, NULL, &val);
+		if (err || val != vals[i] * 5)
+			break;
+	}
+
+	CHECK(i != MAP_SIZE && (err || val != vals[i] * 5),
+	      "bpf_map_push_elem", "err %d value %u\n", err, val);
+
+out:
+	pkt_v4.iph.saddr = 0;
+	bpf_object__close(obj);
+}
+
 int main(void)
 {
+	srand(time(NULL));
+
 	jit_enabled = is_jit_enabled();
 
 	test_pkt_access();
@@ -1757,6 +1854,8 @@ int main(void)
 	test_task_fd_query_rawtp();
 	test_task_fd_query_tp();
 	test_reference_tracking();
+	test_queue_stack_map(QUEUE);
+	test_queue_stack_map(STACK);
 
 	printf("Summary: %d PASSED, %d FAILED\n", pass_cnt, error_cnt);
 	return error_cnt ? EXIT_FAILURE : EXIT_SUCCESS;

tools/testing/selftests/bpf/test_queue_map.c

+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2018 Politecnico di Torino
+#define MAP_TYPE BPF_MAP_TYPE_QUEUE
+#include "test_queue_stack_map.h"

tools/testing/selftests/bpf/test_queue_stack_map.h

+/* SPDX-License-Identifier: GPL-2.0 */
+// Copyright (c) 2018 Politecnico di Torino
+#include <stddef.h>
+#include <string.h>
+#include <linux/bpf.h>
+#include <linux/if_ether.h>
+#include <linux/ip.h>
+#include <linux/pkt_cls.h>
+#include "bpf_helpers.h"
+
+int _version SEC("version") = 1;
+
+struct bpf_map_def __attribute__ ((section("maps"), used)) map_in = {
+	.type = MAP_TYPE,
+	.key_size = 0,
+	.value_size = sizeof(__u32),
+	.max_entries = 32,
+	.map_flags = 0,
+};
+
+struct bpf_map_def __attribute__ ((section("maps"), used)) map_out = {
+	.type = MAP_TYPE,
+	.key_size = 0,
+	.value_size = sizeof(__u32),
+	.max_entries = 32,
+	.map_flags = 0,
+};
+
+SEC("test")
+int _test(struct __sk_buff *skb)
+{
+	void *data_end = (void *)(long)skb->data_end;
+	void *data = (void *)(long)skb->data;
+	struct ethhdr *eth = (struct ethhdr *)(data);
+	__u32 value;
+	int err;
+
+	if (eth + 1 > data_end)
+		return TC_ACT_SHOT;
+
+	struct iphdr *iph = (struct iphdr *)(eth + 1);
+
+	if (iph + 1 > data_end)
+		return TC_ACT_SHOT;
+
+	err = bpf_map_pop_elem(&map_in, &value);
+	if (err)
+		return TC_ACT_SHOT;
+
+	iph->daddr = value;
+
+	err = bpf_map_push_elem(&map_out, &iph->saddr, 0);
+	if (err)
+		return TC_ACT_SHOT;
+
+	return TC_ACT_OK;
+}
+
+char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/test_stack_map.c

+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2018 Politecnico di Torino
+#define MAP_TYPE BPF_MAP_TYPE_STACK
+#include "test_queue_stack_map.h"