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bpf: handle pseudo BPF_LD_IMM64 insn

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eBPF programs passed from userspace are using pseudo BPF_LD_IMM64 instructions
to refer to process-local map_fd. Scan the program for such instructions and
if FDs are valid, convert them to 'struct bpf_map' pointers which will be used
by verifier to check access to maps in bpf_map_lookup/update() calls.
If program passes verifier, convert pseudo BPF_LD_IMM64 into generic by dropping
BPF_PSEUDO_MAP_FD flag.

Note that eBPF interpreter is generic and knows nothing about pseudo insns.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov 2014-09-26 00:17:04 -07:00 committed by David S. Miller
parent cbd3570086
commit 0246e64d9a
2 changed files with 153 additions and 0 deletions
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6
include/linux/filter.h
View File

@ -145,6 +145,12 @@ struct bpf_prog_aux;
.off = 0, \
.imm = ((__u64) (IMM)) >> 32 })
#define BPF_PSEUDO_MAP_FD 1
/* pseudo BPF_LD_IMM64 insn used to refer to process-local map_fd */
#define BPF_LD_MAP_FD(DST, MAP_FD) \
BPF_LD_IMM64_RAW(DST, BPF_PSEUDO_MAP_FD, MAP_FD)
/* Short form of mov based on type, BPF_X: dst_reg = src_reg, BPF_K: dst_reg = imm32 */
#define BPF_MOV64_RAW(TYPE, DST, SRC, IMM) \

147
kernel/bpf/verifier.c
View File

@ -125,10 +125,15 @@
* are set to NOT_INIT to indicate that they are no longer readable.
*/
#define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
/* single container for all structs
* one verifier_env per bpf_check() call
*/
struct verifier_env {
struct bpf_prog *prog; /* eBPF program being verified */
struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
u32 used_map_cnt; /* number of used maps */
};
/* verbose verifier prints what it's seeing
@ -300,6 +305,115 @@ static void print_bpf_insn(struct bpf_insn *insn)
}
}
/* return the map pointer stored inside BPF_LD_IMM64 instruction */
static struct bpf_map *ld_imm64_to_map_ptr(struct bpf_insn *insn)
{
u64 imm64 = ((u64) (u32) insn[0].imm) | ((u64) (u32) insn[1].imm) << 32;
return (struct bpf_map *) (unsigned long) imm64;
}
/* look for pseudo eBPF instructions that access map FDs and
* replace them with actual map pointers
*/
static int replace_map_fd_with_map_ptr(struct verifier_env *env)
{
struct bpf_insn *insn = env->prog->insnsi;
int insn_cnt = env->prog->len;
int i, j;
for (i = 0; i < insn_cnt; i++, insn++) {
if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW)) {
struct bpf_map *map;
struct fd f;
if (i == insn_cnt - 1 || insn[1].code != 0 ||
insn[1].dst_reg != 0 || insn[1].src_reg != 0 ||
insn[1].off != 0) {
verbose("invalid bpf_ld_imm64 insn\n");
return -EINVAL;
}
if (insn->src_reg == 0)
/* valid generic load 64-bit imm */
goto next_insn;
if (insn->src_reg != BPF_PSEUDO_MAP_FD) {
verbose("unrecognized bpf_ld_imm64 insn\n");
return -EINVAL;
}
f = fdget(insn->imm);
map = bpf_map_get(f);
if (IS_ERR(map)) {
verbose("fd %d is not pointing to valid bpf_map\n",
insn->imm);
fdput(f);
return PTR_ERR(map);
}
/* store map pointer inside BPF_LD_IMM64 instruction */
insn[0].imm = (u32) (unsigned long) map;
insn[1].imm = ((u64) (unsigned long) map) >> 32;
/* check whether we recorded this map already */
for (j = 0; j < env->used_map_cnt; j++)
if (env->used_maps[j] == map) {
fdput(f);
goto next_insn;
}
if (env->used_map_cnt >= MAX_USED_MAPS) {
fdput(f);
return -E2BIG;
}
/* remember this map */
env->used_maps[env->used_map_cnt++] = map;
/* hold the map. If the program is rejected by verifier,
* the map will be released by release_maps() or it
* will be used by the valid program until it's unloaded
* and all maps are released in free_bpf_prog_info()
*/
atomic_inc(&map->refcnt);
fdput(f);
next_insn:
insn++;
i++;
}
}
/* now all pseudo BPF_LD_IMM64 instructions load valid
* 'struct bpf_map *' into a register instead of user map_fd.
* These pointers will be used later by verifier to validate map access.
*/
return 0;
}
/* drop refcnt of maps used by the rejected program */
static void release_maps(struct verifier_env *env)
{
int i;
for (i = 0; i < env->used_map_cnt; i++)
bpf_map_put(env->used_maps[i]);
}
/* convert pseudo BPF_LD_IMM64 into generic BPF_LD_IMM64 */
static void convert_pseudo_ld_imm64(struct verifier_env *env)
{
struct bpf_insn *insn = env->prog->insnsi;
int insn_cnt = env->prog->len;
int i;
for (i = 0; i < insn_cnt; i++, insn++)
if (insn->code == (BPF_LD | BPF_IMM | BPF_DW))
insn->src_reg = 0;
}
int bpf_check(struct bpf_prog *prog, union bpf_attr *attr)
{
char __user *log_ubuf = NULL;
@ -316,6 +430,8 @@ int bpf_check(struct bpf_prog *prog, union bpf_attr *attr)
if (!env)
return -ENOMEM;
env->prog = prog;
/* grab the mutex to protect few globals used by verifier */
mutex_lock(&bpf_verifier_lock);
@ -342,8 +458,14 @@ int bpf_check(struct bpf_prog *prog, union bpf_attr *attr)
log_level = 0;
}
ret = replace_map_fd_with_map_ptr(env);
if (ret < 0)
goto skip_full_check;
/* ret = do_check(env); */
skip_full_check:
if (log_level && log_len >= log_size - 1) {
BUG_ON(log_len >= log_size);
/* verifier log exceeded user supplied buffer */
@ -357,11 +479,36 @@ int bpf_check(struct bpf_prog *prog, union bpf_attr *attr)
goto free_log_buf;
}
if (ret == 0 && env->used_map_cnt) {
/* if program passed verifier, update used_maps in bpf_prog_info */
prog->aux->used_maps = kmalloc_array(env->used_map_cnt,
sizeof(env->used_maps[0]),
GFP_KERNEL);
if (!prog->aux->used_maps) {
ret = -ENOMEM;
goto free_log_buf;
}
memcpy(prog->aux->used_maps, env->used_maps,
sizeof(env->used_maps[0]) * env->used_map_cnt);
prog->aux->used_map_cnt = env->used_map_cnt;
/* program is valid. Convert pseudo bpf_ld_imm64 into generic
* bpf_ld_imm64 instructions
*/
convert_pseudo_ld_imm64(env);
}
free_log_buf:
if (log_level)
vfree(log_buf);
free_env:
if (!prog->aux->used_maps)
/* if we didn't copy map pointers into bpf_prog_info, release
* them now. Otherwise free_bpf_prog_info() will release them.
*/
release_maps(env);
kfree(env);
mutex_unlock(&bpf_verifier_lock);
return ret;