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.
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 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 <dan...@iogearbox.net>
---
include/linux/bpf.h | 18 ++++++++++++++++++
include/uapi/linux/bpf.h | 10 +++++++++-
kernel/bpf/arraymap.c | 2 +-
kernel/bpf/hashtab.c | 2 +-
kernel/bpf/local_storage.c | 2 +-
kernel/bpf/lpm_trie.c | 2 +-
kernel/bpf/queue_stack_maps.c | 3 +--
kernel/bpf/verifier.c | 30 +++++++++++++++++++++++++++++-
8 files changed, 61 insertions(+), 8 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index bdcc6e2a9977..3f74194dd4f6 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -427,6 +427,24 @@ struct bpf_array {
};
};
+#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;
+}
+
#define MAX_TAIL_CALL_CNT 32
struct bpf_event_entry {
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 8884072e1a46..04b26f59b413 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -287,7 +287,7 @@ 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)
@@ -297,6 +297,14 @@ 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)
+#define BPF_F_ACCESS_MASK (BPF_F_RDONLY | \
+ BPF_F_RDONLY_PROG | \
+ BPF_F_WRONLY | \
+ BPF_F_WRONLY_PROG)
+
/* flags for BPF_PROG_QUERY */
#define BPF_F_QUERY_EFFECTIVE (1U << 0)
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 3e5969c0c979..076dc3d77faf 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -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)
{
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index fed15cf94dca..ab9d51ac80e1 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -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;
diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
index 6b572e2de7fb..3ffe3259da00 100644
--- a/kernel/bpf/local_storage.c
+++ b/kernel/bpf/local_storage.c
@@ -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;
diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index abf1002080df..79c75b1626b8 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -537,7 +537,7 @@ static int trie_delete_elem(struct bpf_map *map, void *_key)
#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)
{
diff --git a/kernel/bpf/queue_stack_maps.c b/kernel/bpf/queue_stack_maps.c
index b384ea9f3254..1eb9ceef075c 100644
--- a/kernel/bpf/queue_stack_maps.c
+++ b/kernel/bpf/queue_stack_maps.c
@@ -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;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3ad05dda6e9d..cdd2cb01f789 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1429,6 +1429,28 @@ 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 into 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)
@@ -2014,7 +2036,9 @@ 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);
@@ -2250,6 +2274,10 @@ 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 */
--
2.17.1
