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bpf: add program side {rd, wr}only support for maps

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This work adds two new map creation flags BPF_F_RDONLY_PROG
and BPF_F_WRONLY_PROG in order to allow for read-only or
write-only BPF maps from a BPF program side.

Today we have BPF_F_RDONLY and BPF_F_WRONLY, but this only
applies to system call side, meaning the BPF program has full
read/write access to the map as usual while bpf(2) calls with
map fd can either only read or write into the map depending
on the flags. BPF_F_RDONLY_PROG and BPF_F_WRONLY_PROG allows
for the exact opposite such that verifier is going to reject
program loads if write into a read-only map or a read into a
write-only map is detected. For read-only map case also some
helpers are forbidden for programs that would alter the map
state such as map deletion, update, etc. As opposed to the two
BPF_F_RDONLY / BPF_F_WRONLY flags, BPF_F_RDONLY_PROG as well
as BPF_F_WRONLY_PROG really do correspond to the map lifetime.

We've enabled this generic map extension to various non-special
maps holding normal user data: array, hash, lru, lpm, local
storage, queue and stack. Further generic map types could be
followed up in future depending on use-case. Main use case
here is to forbid writes into .rodata map values from verifier
side.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2019-04-09 23:20:05 +02:00 committed by Alexei Starovoitov
parent be70bcd53d
commit 591fe9888d
9 changed files with 96 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
include/linux/bpf.h
View File

@ -430,6 +430,35 @@ struct bpf_array {
#define BPF_COMPLEXITY_LIMIT_INSNS 1000000 /* yes. 1M insns */
#define MAX_TAIL_CALL_CNT 32
#define BPF_F_ACCESS_MASK (BPF_F_RDONLY | \
BPF_F_RDONLY_PROG | \
BPF_F_WRONLY | \
BPF_F_WRONLY_PROG)
#define BPF_MAP_CAN_READ BIT(0)
#define BPF_MAP_CAN_WRITE BIT(1)
static inline u32 bpf_map_flags_to_cap(struct bpf_map *map)
{
u32 access_flags = map->map_flags & (BPF_F_RDONLY_PROG | BPF_F_WRONLY_PROG);
/* Combination of BPF_F_RDONLY_PROG | BPF_F_WRONLY_PROG is
* not possible.
*/
if (access_flags & BPF_F_RDONLY_PROG)
return BPF_MAP_CAN_READ;
else if (access_flags & BPF_F_WRONLY_PROG)
return BPF_MAP_CAN_WRITE;
else
return BPF_MAP_CAN_READ | BPF_MAP_CAN_WRITE;
}
static inline bool bpf_map_flags_access_ok(u32 access_flags)
{
return (access_flags & (BPF_F_RDONLY_PROG | BPF_F_WRONLY_PROG)) !=
(BPF_F_RDONLY_PROG | BPF_F_WRONLY_PROG);
}
struct bpf_event_entry {
struct perf_event *event;
struct file *perf_file;

6
include/uapi/linux/bpf.h
View File

@ -294,7 +294,7 @@ enum bpf_attach_type {
#define BPF_OBJ_NAME_LEN 16U
/* Flags for accessing BPF object */
/* Flags for accessing BPF object from syscall side. */
#define BPF_F_RDONLY (1U << 3)
#define BPF_F_WRONLY (1U << 4)
@ -304,6 +304,10 @@ enum bpf_attach_type {
/* Zero-initialize hash function seed. This should only be used for testing. */
#define BPF_F_ZERO_SEED (1U << 6)
/* Flags for accessing BPF object from program side. */
#define BPF_F_RDONLY_PROG (1U << 7)
#define BPF_F_WRONLY_PROG (1U << 8)
/* flags for BPF_PROG_QUERY */
#define BPF_F_QUERY_EFFECTIVE (1U << 0)

6
kernel/bpf/arraymap.c
View File

@ -22,7 +22,7 @@
#include "map_in_map.h"
#define ARRAY_CREATE_FLAG_MASK \
(BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)
(BPF_F_NUMA_NODE | BPF_F_ACCESS_MASK)
static void bpf_array_free_percpu(struct bpf_array *array)
{
@ -63,6 +63,7 @@ int array_map_alloc_check(union bpf_attr *attr)
if (attr->max_entries == 0 || attr->key_size != 4 ||
attr->value_size == 0 ||
attr->map_flags & ~ARRAY_CREATE_FLAG_MASK ||
!bpf_map_flags_access_ok(attr->map_flags) ||
(percpu && numa_node != NUMA_NO_NODE))
return -EINVAL;
@ -472,6 +473,9 @@ static int fd_array_map_alloc_check(union bpf_attr *attr)
/* only file descriptors can be stored in this type of map */
if (attr->value_size != sizeof(u32))
return -EINVAL;
/* Program read-only/write-only not supported for special maps yet. */
if (attr->map_flags & (BPF_F_RDONLY_PROG | BPF_F_WRONLY_PROG))
return -EINVAL;
return array_map_alloc_check(attr);
}

6
kernel/bpf/hashtab.c
View File

@ -23,7 +23,7 @@
#define HTAB_CREATE_FLAG_MASK \
(BPF_F_NO_PREALLOC | BPF_F_NO_COMMON_LRU | BPF_F_NUMA_NODE | \
BPF_F_RDONLY | BPF_F_WRONLY | BPF_F_ZERO_SEED)
BPF_F_ACCESS_MASK | BPF_F_ZERO_SEED)
struct bucket {
struct hlist_nulls_head head;
@ -262,8 +262,8 @@ static int htab_map_alloc_check(union bpf_attr *attr)
/* Guard against local DoS, and discourage production use. */
return -EPERM;
if (attr->map_flags & ~HTAB_CREATE_FLAG_MASK)
/* reserved bits should not be used */
if (attr->map_flags & ~HTAB_CREATE_FLAG_MASK ||
!bpf_map_flags_access_ok(attr->map_flags))
return -EINVAL;
if (!lru && percpu_lru)

6
kernel/bpf/local_storage.c
View File

@ -14,7 +14,7 @@ DEFINE_PER_CPU(struct bpf_cgroup_storage*, bpf_cgroup_storage[MAX_BPF_CGROUP_STO
#ifdef CONFIG_CGROUP_BPF
#define LOCAL_STORAGE_CREATE_FLAG_MASK \
(BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)
(BPF_F_NUMA_NODE | BPF_F_ACCESS_MASK)
struct bpf_cgroup_storage_map {
struct bpf_map map;
@ -282,8 +282,8 @@ static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
if (attr->value_size > PAGE_SIZE)
return ERR_PTR(-E2BIG);
if (attr->map_flags & ~LOCAL_STORAGE_CREATE_FLAG_MASK)
/* reserved bits should not be used */
if (attr->map_flags & ~LOCAL_STORAGE_CREATE_FLAG_MASK ||
!bpf_map_flags_access_ok(attr->map_flags))
return ERR_PTR(-EINVAL);
if (attr->max_entries)

3
kernel/bpf/lpm_trie.c
View File

@ -538,7 +538,7 @@ out:
#define LPM_KEY_SIZE_MIN LPM_KEY_SIZE(LPM_DATA_SIZE_MIN)
#define LPM_CREATE_FLAG_MASK (BPF_F_NO_PREALLOC | BPF_F_NUMA_NODE | \
BPF_F_RDONLY | BPF_F_WRONLY)
BPF_F_ACCESS_MASK)
static struct bpf_map *trie_alloc(union bpf_attr *attr)
{
@ -553,6 +553,7 @@ static struct bpf_map *trie_alloc(union bpf_attr *attr)
if (attr->max_entries == 0 ||
!(attr->map_flags & BPF_F_NO_PREALLOC) ||
attr->map_flags & ~LPM_CREATE_FLAG_MASK ||
!bpf_map_flags_access_ok(attr->map_flags) ||
attr->key_size < LPM_KEY_SIZE_MIN ||
attr->key_size > LPM_KEY_SIZE_MAX ||
attr->value_size < LPM_VAL_SIZE_MIN ||

6
kernel/bpf/queue_stack_maps.c
View File

@ -11,8 +11,7 @@
#include "percpu_freelist.h"
#define QUEUE_STACK_CREATE_FLAG_MASK \
(BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)
(BPF_F_NUMA_NODE | BPF_F_ACCESS_MASK)
struct bpf_queue_stack {
struct bpf_map map;
@ -52,7 +51,8 @@ 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 == 0 ||
attr->map_flags & ~QUEUE_STACK_CREATE_FLAG_MASK)
attr->map_flags & ~QUEUE_STACK_CREATE_FLAG_MASK ||
!bpf_map_flags_access_ok(attr->map_flags))
return -EINVAL;
if (attr->value_size > KMALLOC_MAX_SIZE)

2
kernel/bpf/syscall.c
View File

@ -501,6 +501,8 @@ static int map_check_btf(struct bpf_map *map, const struct btf *btf,
map->spin_lock_off = btf_find_spin_lock(btf, value_type);
if (map_value_has_spin_lock(map)) {
if (map->map_flags & BPF_F_RDONLY_PROG)
return -EACCES;
if (map->map_type != BPF_MAP_TYPE_HASH &&
map->map_type != BPF_MAP_TYPE_ARRAY &&
map->map_type != BPF_MAP_TYPE_CGROUP_STORAGE)

46
kernel/bpf/verifier.c
View File

@ -1439,6 +1439,28 @@ static int check_stack_access(struct bpf_verifier_env *env,
return 0;
}
static int check_map_access_type(struct bpf_verifier_env *env, u32 regno,
int off, int size, enum bpf_access_type type)
{
struct bpf_reg_state *regs = cur_regs(env);
struct bpf_map *map = regs[regno].map_ptr;
u32 cap = bpf_map_flags_to_cap(map);
if (type == BPF_WRITE && !(cap & BPF_MAP_CAN_WRITE)) {
verbose(env, "write into map forbidden, value_size=%d off=%d size=%d\n",
map->value_size, off, size);
return -EACCES;
}
if (type == BPF_READ && !(cap & BPF_MAP_CAN_READ)) {
verbose(env, "read from map forbidden, value_size=%d off=%d size=%d\n",
map->value_size, off, size);
return -EACCES;
}
return 0;
}
/* check read/write into map element returned by bpf_map_lookup_elem() */
static int __check_map_access(struct bpf_verifier_env *env, u32 regno, int off,
int size, bool zero_size_allowed)
@ -2024,7 +2046,9 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
verbose(env, "R%d leaks addr into map\n", value_regno);
return -EACCES;
}
err = check_map_access_type(env, regno, off, size, t);
if (err)
return err;
err = check_map_access(env, regno, off, size, false);
if (!err && t == BPF_READ && value_regno >= 0)
mark_reg_unknown(env, regs, value_regno);
@ -2327,6 +2351,10 @@ static int check_helper_mem_access(struct bpf_verifier_env *env, int regno,
return check_packet_access(env, regno, reg->off, access_size,
zero_size_allowed);
case PTR_TO_MAP_VALUE:
if (check_map_access_type(env, regno, reg->off, access_size,
meta && meta->raw_mode ? BPF_WRITE :
BPF_READ))
return -EACCES;
return check_map_access(env, regno, reg->off, access_size,
zero_size_allowed);
default: /* scalar_value|ptr_to_stack or invalid ptr */
@ -3059,6 +3087,7 @@ record_func_map(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
int func_id, int insn_idx)
{
struct bpf_insn_aux_data *aux = &env->insn_aux_data[insn_idx];
struct bpf_map *map = meta->map_ptr;
if (func_id != BPF_FUNC_tail_call &&
func_id != BPF_FUNC_map_lookup_elem &&
@ -3069,11 +3098,24 @@ record_func_map(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
func_id != BPF_FUNC_map_peek_elem)
return 0;
if (meta->map_ptr == NULL) {
if (map == NULL) {
verbose(env, "kernel subsystem misconfigured verifier\n");
return -EINVAL;
}
/* In case of read-only, some additional restrictions
* need to be applied in order to prevent altering the
* state of the map from program side.
*/
if ((map->map_flags & BPF_F_RDONLY_PROG) &&
(func_id == BPF_FUNC_map_delete_elem ||
func_id == BPF_FUNC_map_update_elem ||
func_id == BPF_FUNC_map_push_elem ||
func_id == BPF_FUNC_map_pop_elem)) {
verbose(env, "write into map forbidden\n");
return -EACCES;
}
if (!BPF_MAP_PTR(aux->map_state))
bpf_map_ptr_store(aux, meta->map_ptr,
meta->map_ptr->unpriv_array);