Message-ID: <20180918232753.2vk6u256ag27cjgo@ast-mbp>
Date:   Tue, 18 Sep 2018 16:27:54 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Mauricio Vasquez B <mauricio.vasquez@...ito.it>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        Yonghong Song <yhs@...com>
Subject: Re: [RFC PATCH bpf-next v3 4/7] bpf: add bpf queue and stack maps

On Tue, Sep 18, 2018 at 06:52:51AM +0200, Mauricio Vasquez B wrote:
> Implement two new kind of maps that support the peek, push and pop
> operations.
> 
> A use case for this is to keep track of a pool of elements, like
> network ports in a SNAT.
> 
> Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@...ito.it>
> ---
>  include/linux/bpf.h           |    3 
>  include/linux/bpf_types.h     |    2 
>  include/uapi/linux/bpf.h      |   30 ++++
>  kernel/bpf/Makefile           |    2 
>  kernel/bpf/core.c             |    3 
>  kernel/bpf/helpers.c          |   98 ++++++++++++++
>  kernel/bpf/queue_stack_maps.c |  291 +++++++++++++++++++++++++++++++++++++++++
>  kernel/bpf/verifier.c         |    5 +
>  net/core/filter.c             |    6 +
>  9 files changed, 437 insertions(+), 3 deletions(-)
>  create mode 100644 kernel/bpf/queue_stack_maps.c
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index c63a44381d3f..8e924b5c5a0e 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -807,6 +807,9 @@ 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;
> diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> index 33f7f574b983..903a446f14c3 100644
> --- a/include/linux/bpf_types.h
> +++ b/include/linux/bpf_types.h
> @@ -67,3 +67,5 @@ 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)
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 4cda584c6640..c899386dcb2b 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -128,6 +128,8 @@ enum bpf_map_type {
>  	BPF_MAP_TYPE_SOCKHASH,
>  	BPF_MAP_TYPE_CGROUP_STORAGE,
>  	BPF_MAP_TYPE_REUSEPORT_SOCKARRAY,
> +	BPF_MAP_TYPE_QUEUE,
> +	BPF_MAP_TYPE_STACK,
>  };
>  
>  enum bpf_prog_type {
> @@ -460,6 +462,29 @@ 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, u32 len,
> + * 			 u64 flags)

since we're passing <=8 byte value there is no need for pointer and len.
Lower bits of 'u64 value' would be faster and easier to use from bpf prog side.

> + * 	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, u32 len)
> + * 	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, u32 len)

for pop/peak helpers the 'void *value' makes sense,
but 'len' doesn't need to be there and doesn't need to be checked in runtime.
Verifier should be able to do that.
More below.

> + * 	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
> @@ -2227,7 +2252,10 @@ union bpf_attr {
>  	FN(get_current_cgroup_id),	\
>  	FN(get_local_storage),		\
>  	FN(sk_select_reuseport),	\
> -	FN(skb_ancestor_cgroup_id),
> +	FN(skb_ancestor_cgroup_id),	\
> +	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
> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> index e656bce87c8f..2d77bc5b2aca 100644
> --- a/kernel/bpf/Makefile
> +++ b/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)
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 3f5bf1af0826..8d2db076d123 100644
> --- a/kernel/bpf/core.c
> +++ b/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;
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 1991466b8327..5f364e6acaf1 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -76,6 +76,104 @@ const struct bpf_func_proto bpf_map_delete_elem_proto = {
>  	.arg2_type	= ARG_PTR_TO_MAP_KEY,
>  };
>  
> +BPF_CALL_4(bpf_map_push_elem, struct bpf_map *, map, void *, value, u32 size,
> +	   u64, flags)
> +{
> +	if (map->value_size != size)
> +		return -EINVAL;
> +
> +	return map->ops->map_update_elem(map, NULL, 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_MEM,
> +	.arg3_type	= ARG_CONST_SIZE,
> +	.arg4_type	= ARG_ANYTHING,
> +};
> +
> +BPF_CALL_3(bpf_map_pop_elem, struct bpf_map *, map, void *, value, u32, size)
> +{
> +	void *ptr;
> +
> +	if (map->value_size != size)
> +		return -EINVAL;
> +
> +	ptr = map->ops->map_lookup_and_delete_elem(map, NULL);
> +	if (!ptr)
> +		return -ENOENT;
> +
> +	switch (size) {
> +	case 1:
> +		*(u8 *) value = *(u8 *) ptr;
> +		break;
> +	case 2:
> +		*(u16 *) value = *(u16 *) ptr;
> +		break;
> +	case 4:
> +		*(u32 *) value = *(u32 *) ptr;
> +		break;
> +	case 8:
> +		*(u64 *) value = *(u64 *) ptr;
> +		break;

this is inefficient. can we pass value ptr into ops and let it populate it?

> +	}
> +
> +	return 0;
> +}
> +
> +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_MEM,
> +	.arg3_type	= ARG_CONST_SIZE,
> +};
> +
> +BPF_CALL_3(bpf_map_peek_elem, struct bpf_map *, map, void *, value, u32, size)
> +{
> +	void *ptr;
> +
> +	if (map->value_size != size)
> +		return -EINVAL;
> +
> +	ptr = map->ops->map_lookup_elem(map, NULL);
> +	if (!ptr)
> +		return -ENOENT;
> +
> +	switch (size) {
> +	case 1:
> +		*(u8 *) value = *(u8 *) ptr;
> +		break;
> +	case 2:
> +		*(u16 *) value = *(u16 *) ptr;
> +		break;
> +	case 4:
> +		*(u32 *) value = *(u32 *) ptr;
> +		break;
> +	case 8:
> +		*(u64 *) value = *(u64 *) ptr;
> +		break;
> +	}
> +
> +	return 0;
> +}
> +
> +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_MEM,
> +	.arg3_type	= ARG_CONST_SIZE,
> +};
> +
>  const struct bpf_func_proto bpf_get_prandom_u32_proto = {
>  	.func		= bpf_user_rnd_u32,
>  	.gpl_only	= false,
> diff --git a/kernel/bpf/queue_stack_maps.c b/kernel/bpf/queue_stack_maps.c
> new file mode 100644
> index 000000000000..10c081f3f02b
> --- /dev/null
> +++ b/kernel/bpf/queue_stack_maps.c
> @@ -0,0 +1,291 @@
> +// 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 index_mask;
> +	u32 count;
> +
> +	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->count == 0;
> +}
> +
> +static bool queue_stack_map_is_full(struct bpf_queue_stack *qs)
> +{
> +	return qs->count == qs->map.max_entries;
> +}
> +
> +/* 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->value_size != 1 && attr->value_size != 2 &&
> +	    attr->value_size != 4 && attr->value_size != 8) ||
> +	    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);
> +	u32 max_entries, value_size, index_mask;
> +	u64 queue_size, cost, mask64;
> +	struct bpf_queue_stack *qs;
> +
> +	max_entries = attr->max_entries;
> +	value_size = attr->value_size;
> +
> +	/* From arraymap.c:
> +	 * On 32 bit archs roundup_pow_of_two() with max_entries that has
> +	 * upper most bit set in u32 space is undefined behavior due to
> +	 * resulting 1U << 32, so do it manually here in u64 space.
> +	 */
> +	mask64 = fls_long(max_entries - 1);
> +	mask64 = 1ULL << mask64;
> +	mask64 -= 1;
> +
> +	index_mask = mask64;
> +
> +	/* Round up queue size to nearest power of 2 */
> +	max_entries = index_mask + 1;
> +	/* Check for overflows. */
> +	if (max_entries < attr->max_entries)
> +		return ERR_PTR(-E2BIG);
> +
> +	queue_size = sizeof(*qs) + (u64) value_size * max_entries;
> +
> +	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->index_mask = index_mask;
> +
> +	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 void *__queue_map_lookup(struct bpf_map *map, bool delete)
> +{
> +	struct bpf_queue_stack *qs = bpf_queue_stack(map);
> +	unsigned long flags;
> +	void *ptr = NULL;
> +
> +	raw_spin_lock_irqsave(&qs->lock, flags);
> +
> +	if (queue_stack_map_is_empty(qs))
> +		goto out;
> +
> +	ptr = &qs->elements[qs->tail * qs->map.value_size];
> +
> +	if (delete) {
> +		qs->tail = (qs->tail + 1) & qs->index_mask;
> +		qs->count--;
> +	}
> +
> +out:
> +	raw_spin_unlock_irqrestore(&qs->lock, flags);
> +	return ptr;
> +}
> +
> +
> +static void *__stack_map_lookup(struct bpf_map *map, bool delete)
> +{
> +	struct bpf_queue_stack *qs = bpf_queue_stack(map);
> +	unsigned long flags;
> +	void *ptr = NULL;
> +	u32 index;
> +
> +	raw_spin_lock_irqsave(&qs->lock, flags);
> +
> +	if (queue_stack_map_is_empty(qs))
> +		goto out;
> +
> +	index = (qs->head - 1) & qs->index_mask;
> +	ptr = &qs->elements[index * qs->map.value_size];
> +
> +	if (delete) {
> +		qs->head = (qs->head - 1) & qs->index_mask;
> +		qs->count--;
> +	}
> +
> +out:
> +	raw_spin_unlock_irqrestore(&qs->lock, flags);

here it's racing with another cpu accessing the same map.
rcu doesn't protect from this particular qs->element being reused
by another cpu.

> +	return ptr;

say, stack is full. one cpu is doing pop(), getting this ptr,
while another cpu doing push() and overwriting this memory.

> +}
> +
> +/* Called from syscall or from eBPF program */
> +static void *queue_map_lookup_elem(struct bpf_map *map, void *key)
> +{
> +	return __queue_map_lookup(map, false);
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
> +{
> +	return __stack_map_lookup(map, false);
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static void *queue_map_lookup_and_delete_elem(struct bpf_map *map, void *key)
> +{
> +	return __queue_map_lookup(map, true);
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static void *stack_map_lookup_and_delete_elem(struct bpf_map *map, void *key)
> +{
> +	return __stack_map_lookup(map, true);
> +}
> +
> +/* Called from syscall or from eBPF program */
> +static int queue_stack_map_update_elem(struct bpf_map *map, void *key,
> +				       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 stqueue_map_is_preallocack 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 */
> +		qs->tail = (qs->tail + 1) & qs->index_mask;
> +		qs->count--;
> +	}
> +
> +	dst = &qs->elements[qs->head * qs->map.value_size];
> +
> +	switch (qs->map.value_size) {
> +	case 1:
> +		*(u8 *) dst = *(u8 *) value;
> +		break;
> +	case 2:
> +		*(u16 *) dst = *(u16 *) value;
> +		break;
> +	case 4:
> +		*(u32 *) dst = *(u32 *) value;
> +		break;
> +	case 8:
> +		*(u64 *) dst = *(u64 *) value;
> +		break;
> +	}
> +
> +	qs->head = (qs->head + 1) & qs->index_mask;
> +	qs->count++;
> +
> +out:
> +	raw_spin_unlock_irqrestore(&qs->lock, irq_flags);
> +	return err;
> +}
> +
> +/* 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_map_lookup_elem,
> +	.map_lookup_and_delete_elem = queue_map_lookup_and_delete_elem,
> +	.map_update_elem = queue_stack_map_update_elem,
> +	.map_delete_elem = queue_stack_map_delete_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 = stack_map_lookup_elem,
> +	.map_lookup_and_delete_elem = stack_map_lookup_and_delete_elem,
> +	.map_update_elem = queue_stack_map_update_elem,
> +	.map_delete_elem = queue_stack_map_delete_elem,
> +	.map_get_next_key = queue_stack_map_get_next_key,
> +};
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index f4ff0c569e54..b9e005188f0e 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2369,7 +2369,10 @@ 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) {
> diff --git a/net/core/filter.c b/net/core/filter.c
> index feb578506009..c7b73376c23a 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4839,6 +4839,12 @@ 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:
> 

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