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bpf: permits narrower load from bpf program context fields

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Currently, verifier will reject a program if it contains an
narrower load from the bpf context structure. For example,
        __u8 h = __sk_buff->hash, or
        __u16 p = __sk_buff->protocol
        __u32 sample_period = bpf_perf_event_data->sample_period
which are narrower loads of 4-byte or 8-byte field.

This patch solves the issue by:
  . Introduce a new parameter ctx_field_size to carry the
    field size of narrower load from prog type
    specific *__is_valid_access validator back to verifier.
  . The non-zero ctx_field_size for a memory access indicates
    (1). underlying prog type specific convert_ctx_accesses
         supporting non-whole-field access
    (2). the current insn is a narrower or whole field access.
  . In verifier, for such loads where load memory size is
    less than ctx_field_size, verifier transforms it
    to a full field load followed by proper masking.
  . Currently, __sk_buff and bpf_perf_event_data->sample_period
    are supporting narrowing loads.
  . Narrower stores are still not allowed as typical ctx stores
    are just normal stores.

Because of this change, some tests in verifier will fail and
these tests are removed. As a bonus, rename some out of bound
__sk_buff->cb access to proper field name and remove two
redundant "skb cb oob" tests.

Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yonghong Song 2017-06-13 15:52:13 -07:00 committed by David S. Miller
parent a88e2676a6
commit 31fd85816d
6 changed files with 124 additions and 119 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
include/linux/bpf.h
View file

@ -157,7 +157,7 @@ struct bpf_verifier_ops {
* with 'type' (read or write) is allowed
*/
bool (*is_valid_access)(int off, int size, enum bpf_access_type type,
enum bpf_reg_type *reg_type);
enum bpf_reg_type *reg_type, int *ctx_field_size);
int (*gen_prologue)(struct bpf_insn *insn, bool direct_write,
const struct bpf_prog *prog);
u32 (*convert_ctx_access)(enum bpf_access_type type,

1
include/linux/bpf_verifier.h
View file

@ -73,6 +73,7 @@ struct bpf_insn_aux_data {
enum bpf_reg_type ptr_type; /* pointer type for load/store insns */
struct bpf_map *map_ptr; /* pointer for call insn into lookup_elem */
};
int ctx_field_size; /* the ctx field size for load/store insns, maybe 0 */
};
#define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */

71
kernel/bpf/verifier.c
View file

@ -758,15 +758,26 @@ static int check_packet_access(struct bpf_verifier_env *env, u32 regno, int off,
}
/* check access to 'struct bpf_context' fields */
static int check_ctx_access(struct bpf_verifier_env *env, int off, int size,
static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off, int size,
enum bpf_access_type t, enum bpf_reg_type *reg_type)
{
int ctx_field_size = 0;
/* for analyzer ctx accesses are already validated and converted */
if (env->analyzer_ops)
return 0;
if (env->prog->aux->ops->is_valid_access &&
env->prog->aux->ops->is_valid_access(off, size, t, reg_type)) {
env->prog->aux->ops->is_valid_access(off, size, t, reg_type, &ctx_field_size)) {
/* a non zero ctx_field_size indicates:
* . For this field, the prog type specific ctx conversion algorithm
* only supports whole field access.
* . This ctx access is a candiate for later verifier transformation
* to load the whole field and then apply a mask to get correct result.
*/
if (ctx_field_size)
env->insn_aux_data[insn_idx].ctx_field_size = ctx_field_size;
/* remember the offset of last byte accessed in ctx */
if (env->prog->aux->max_ctx_offset < off + size)
env->prog->aux->max_ctx_offset = off + size;
@ -868,7 +879,7 @@ static int check_ptr_alignment(struct bpf_verifier_env *env,
* if t==write && value_regno==-1, some unknown value is stored into memory
* if t==read && value_regno==-1, don't care what we read from memory
*/
static int check_mem_access(struct bpf_verifier_env *env, u32 regno, int off,
static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regno, int off,
int bpf_size, enum bpf_access_type t,
int value_regno)
{
@ -911,7 +922,7 @@ static int check_mem_access(struct bpf_verifier_env *env, u32 regno, int off,
verbose("R%d leaks addr into ctx\n", value_regno);
return -EACCES;
}
err = check_ctx_access(env, off, size, t, &reg_type);
err = check_ctx_access(env, insn_idx, off, size, t, &reg_type);
if (!err && t == BPF_READ && value_regno >= 0) {
mark_reg_unknown_value_and_range(state->regs,
value_regno);
@ -972,7 +983,7 @@ static int check_mem_access(struct bpf_verifier_env *env, u32 regno, int off,
return err;
}
static int check_xadd(struct bpf_verifier_env *env, struct bpf_insn *insn)
static int check_xadd(struct bpf_verifier_env *env, int insn_idx, struct bpf_insn *insn)
{
struct bpf_reg_state *regs = env->cur_state.regs;
int err;
@ -994,13 +1005,13 @@ static int check_xadd(struct bpf_verifier_env *env, struct bpf_insn *insn)
return err;
/* check whether atomic_add can read the memory */
err = check_mem_access(env, insn->dst_reg, insn->off,
err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_READ, -1);
if (err)
return err;
/* check whether atomic_add can write into the same memory */
return check_mem_access(env, insn->dst_reg, insn->off,
return check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE, -1);
}
@ -1416,7 +1427,7 @@ static int check_call(struct bpf_verifier_env *env, int func_id, int insn_idx)
* is inferred from register state.
*/
for (i = 0; i < meta.access_size; i++) {
err = check_mem_access(env, meta.regno, i, BPF_B, BPF_WRITE, -1);
err = check_mem_access(env, insn_idx, meta.regno, i, BPF_B, BPF_WRITE, -1);
if (err)
return err;
}
@ -2993,18 +3004,12 @@ static int do_check(struct bpf_verifier_env *env)
/* check that memory (src_reg + off) is readable,
* the state of dst_reg will be updated by this func
*/
err = check_mem_access(env, insn->src_reg, insn->off,
err = check_mem_access(env, insn_idx, insn->src_reg, insn->off,
BPF_SIZE(insn->code), BPF_READ,
insn->dst_reg);
if (err)
return err;
if (BPF_SIZE(insn->code) != BPF_W &&
BPF_SIZE(insn->code) != BPF_DW) {
insn_idx++;
continue;
}
prev_src_type = &env->insn_aux_data[insn_idx].ptr_type;
if (*prev_src_type == NOT_INIT) {
@ -3032,7 +3037,7 @@ static int do_check(struct bpf_verifier_env *env)
enum bpf_reg_type *prev_dst_type, dst_reg_type;
if (BPF_MODE(insn->code) == BPF_XADD) {
err = check_xadd(env, insn);
err = check_xadd(env, insn_idx, insn);
if (err)
return err;
insn_idx++;
@ -3051,7 +3056,7 @@ static int do_check(struct bpf_verifier_env *env)
dst_reg_type = regs[insn->dst_reg].type;
/* check that memory (dst_reg + off) is writeable */
err = check_mem_access(env, insn->dst_reg, insn->off,
err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE,
insn->src_reg);
if (err)
@ -3080,7 +3085,7 @@ static int do_check(struct bpf_verifier_env *env)
return err;
/* check that memory (dst_reg + off) is writeable */
err = check_mem_access(env, insn->dst_reg, insn->off,
err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE,
-1);
if (err)
@ -3383,7 +3388,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
struct bpf_insn insn_buf[16], *insn;
struct bpf_prog *new_prog;
enum bpf_access_type type;
int i, cnt, delta = 0;
int i, cnt, off, size, ctx_field_size, is_narrower_load, delta = 0;
if (ops->gen_prologue) {
cnt = ops->gen_prologue(insn_buf, env->seen_direct_write,
@ -3423,11 +3428,39 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
if (env->insn_aux_data[i + delta].ptr_type != PTR_TO_CTX)
continue;
off = insn->off;
size = bpf_size_to_bytes(BPF_SIZE(insn->code));
ctx_field_size = env->insn_aux_data[i + delta].ctx_field_size;
is_narrower_load = (type == BPF_READ && size < ctx_field_size);
/* If the read access is a narrower load of the field,
* convert to a 4/8-byte load, to minimum program type specific
* convert_ctx_access changes. If conversion is successful,
* we will apply proper mask to the result.
*/
if (is_narrower_load) {
int size_code = BPF_H;
if (ctx_field_size == 4)
size_code = BPF_W;
else if (ctx_field_size == 8)
size_code = BPF_DW;
insn->off = off & ~(ctx_field_size - 1);
insn->code = BPF_LDX | BPF_MEM | size_code;
}
cnt = ops->convert_ctx_access(type, insn, insn_buf, env->prog);
if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
verbose("bpf verifier is misconfigured\n");
return -EINVAL;
}
if (is_narrower_load) {
if (ctx_field_size <= 4)
insn_buf[cnt++] = BPF_ALU32_IMM(BPF_AND, insn->dst_reg,
(1 << size * 8) - 1);
else
insn_buf[cnt++] = BPF_ALU64_IMM(BPF_AND, insn->dst_reg,
(1 << size * 8) - 1);
}
new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
if (!new_prog)

21
kernel/trace/bpf_trace.c
View file

@ -479,7 +479,7 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
/* bpf+kprobe programs can access fields of 'struct pt_regs' */
static bool kprobe_prog_is_valid_access(int off, int size, enum bpf_access_type type,
enum bpf_reg_type *reg_type)
enum bpf_reg_type *reg_type, int *ctx_field_size)
{
if (off < 0 || off >= sizeof(struct pt_regs))
return false;
@ -562,7 +562,7 @@ static const struct bpf_func_proto *tp_prog_func_proto(enum bpf_func_id func_id)
}
static bool tp_prog_is_valid_access(int off, int size, enum bpf_access_type type,
enum bpf_reg_type *reg_type)
enum bpf_reg_type *reg_type, int *ctx_field_size)
{
if (off < sizeof(void *) || off >= PERF_MAX_TRACE_SIZE)
return false;
@ -581,17 +581,26 @@ const struct bpf_verifier_ops tracepoint_prog_ops = {
};
static bool pe_prog_is_valid_access(int off, int size, enum bpf_access_type type,
enum bpf_reg_type *reg_type)
enum bpf_reg_type *reg_type, int *ctx_field_size)
{
int sample_period_off;
if (off < 0 || off >= sizeof(struct bpf_perf_event_data))
return false;
if (type != BPF_READ)
return false;
if (off % size != 0)
return false;
if (off == offsetof(struct bpf_perf_event_data, sample_period)) {
if (size != sizeof(u64))
return false;
/* permit 1, 2, 4 byte narrower and 8 normal read access to sample_period */
sample_period_off = offsetof(struct bpf_perf_event_data, sample_period);
if (off >= sample_period_off && off < sample_period_off + sizeof(__u64)) {
*ctx_field_size = 8;
#ifdef __LITTLE_ENDIAN
return (off & 0x7) == 0 && size <= 8 && (size & (size - 1)) == 0;
#else
return ((off & 0x7) + size) == 8 && size <= 8 && (size & (size - 1)) == 0;
#endif
} else {
if (size != sizeof(long))
return false;

56
net/core/filter.c
View file

@ -2856,7 +2856,8 @@ lwt_xmit_func_proto(enum bpf_func_id func_id)
}
}
static bool __is_valid_access(int off, int size)
static bool __is_valid_access(int off, int size, enum bpf_access_type type,
int *ctx_field_size)
{
if (off < 0 || off >= sizeof(struct __sk_buff))
return false;
@ -2872,9 +2873,27 @@ static bool __is_valid_access(int off, int size)
offsetof(struct __sk_buff, cb[4]) + sizeof(__u32))
return false;
break;
default:
case offsetof(struct __sk_buff, data) ...
offsetof(struct __sk_buff, data) + sizeof(__u32) - 1:
case offsetof(struct __sk_buff, data_end) ...
offsetof(struct __sk_buff, data_end) + sizeof(__u32) - 1:
if (size != sizeof(__u32))
return false;
break;
default:
/* permit narrower load for not cb/data/data_end fields */
*ctx_field_size = 4;
if (type == BPF_WRITE) {
if (size != sizeof(__u32))
return false;
} else {
if (size != sizeof(__u32))
#ifdef __LITTLE_ENDIAN
return (off & 0x3) == 0 && (size == 1 || size == 2);
#else
return (off & 0x3) + size == 4 && (size == 1 || size == 2);
#endif
}
}
return true;
@ -2882,12 +2901,16 @@ static bool __is_valid_access(int off, int size)
static bool sk_filter_is_valid_access(int off, int size,
enum bpf_access_type type,
enum bpf_reg_type *reg_type)
enum bpf_reg_type *reg_type,
int *ctx_field_size)
{
switch (off) {
case offsetof(struct __sk_buff, tc_classid):
case offsetof(struct __sk_buff, data):
case offsetof(struct __sk_buff, data_end):
case offsetof(struct __sk_buff, tc_classid) ...
offsetof(struct __sk_buff, tc_classid) + sizeof(__u32) - 1:
case offsetof(struct __sk_buff, data) ...
offsetof(struct __sk_buff, data) + sizeof(__u32) - 1:
case offsetof(struct __sk_buff, data_end) ...
offsetof(struct __sk_buff, data_end) + sizeof(__u32) - 1:
return false;
}
@ -2901,15 +2924,17 @@ static bool sk_filter_is_valid_access(int off, int size,
}
}
return __is_valid_access(off, size);
return __is_valid_access(off, size, type, ctx_field_size);
}
static bool lwt_is_valid_access(int off, int size,
enum bpf_access_type type,
enum bpf_reg_type *reg_type)
enum bpf_reg_type *reg_type,
int *ctx_field_size)
{
switch (off) {
case offsetof(struct __sk_buff, tc_classid):
case offsetof(struct __sk_buff, tc_classid) ...
offsetof(struct __sk_buff, tc_classid) + sizeof(__u32) - 1:
return false;
}
@ -2934,12 +2959,13 @@ static bool lwt_is_valid_access(int off, int size,
break;
}
return __is_valid_access(off, size);
return __is_valid_access(off, size, type, ctx_field_size);
}
static bool sock_filter_is_valid_access(int off, int size,
enum bpf_access_type type,
enum bpf_reg_type *reg_type)
enum bpf_reg_type *reg_type,
int *ctx_field_size)
{
if (type == BPF_WRITE) {
switch (off) {
@ -3002,7 +3028,8 @@ static int tc_cls_act_prologue(struct bpf_insn *insn_buf, bool direct_write,
static bool tc_cls_act_is_valid_access(int off, int size,
enum bpf_access_type type,
enum bpf_reg_type *reg_type)
enum bpf_reg_type *reg_type,
int *ctx_field_size)
{
if (type == BPF_WRITE) {
switch (off) {
@ -3027,7 +3054,7 @@ static bool tc_cls_act_is_valid_access(int off, int size,
break;
}
return __is_valid_access(off, size);
return __is_valid_access(off, size, type, ctx_field_size);
}
static bool __is_valid_xdp_access(int off, int size)
@ -3044,7 +3071,8 @@ static bool __is_valid_xdp_access(int off, int size)
static bool xdp_is_valid_access(int off, int size,
enum bpf_access_type type,
enum bpf_reg_type *reg_type)
enum bpf_reg_type *reg_type,
int *ctx_field_size)
{
if (type == BPF_WRITE)
return false;

92
tools/testing/selftests/bpf/test_verifier.c
View file

@ -1073,44 +1073,22 @@ static struct bpf_test tests[] = {
.result = ACCEPT,
},
{
"check cb access: byte, oob 1",
"__sk_buff->hash, offset 0, byte store not permitted",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_STX_MEM(BPF_B, BPF_REG_1, BPF_REG_0,
offsetof(struct __sk_buff, cb[4]) + 4),
offsetof(struct __sk_buff, hash)),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check cb access: byte, oob 2",
"__sk_buff->tc_index, offset 3, byte store not permitted",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_STX_MEM(BPF_B, BPF_REG_1, BPF_REG_0,
offsetof(struct __sk_buff, cb[0]) - 1),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check cb access: byte, oob 3",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, cb[4]) + 4),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check cb access: byte, oob 4",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, cb[0]) - 1),
offsetof(struct __sk_buff, tc_index) + 3),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
@ -1188,44 +1166,22 @@ static struct bpf_test tests[] = {
.result = REJECT,
},
{
"check cb access: half, oob 1",
"check __sk_buff->hash, offset 0, half store not permitted",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_STX_MEM(BPF_H, BPF_REG_1, BPF_REG_0,
offsetof(struct __sk_buff, cb[4]) + 4),
offsetof(struct __sk_buff, hash)),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check cb access: half, oob 2",
"check __sk_buff->tc_index, offset 2, half store not permitted",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_STX_MEM(BPF_H, BPF_REG_1, BPF_REG_0,
offsetof(struct __sk_buff, cb[0]) - 2),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check cb access: half, oob 3",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, cb[4]) + 4),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check cb access: half, oob 4",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, cb[0]) - 2),
offsetof(struct __sk_buff, tc_index) + 2),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
@ -1366,28 +1322,6 @@ static struct bpf_test tests[] = {
},
{
"check cb access: double, oob 2",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0,
offsetof(struct __sk_buff, cb[4]) + 8),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check cb access: double, oob 3",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0,
offsetof(struct __sk_buff, cb[0]) - 8),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check cb access: double, oob 4",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1,
@ -1398,22 +1332,22 @@ static struct bpf_test tests[] = {
.result = REJECT,
},
{
"check cb access: double, oob 5",
"check __sk_buff->ifindex dw store not permitted",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, cb[4]) + 8),
BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0,
offsetof(struct __sk_buff, ifindex)),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check cb access: double, oob 6",
"check __sk_buff->ifindex dw load not permitted",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, cb[0]) - 8),
offsetof(struct __sk_buff, ifindex)),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",