Lift verifier restriction to use BPF_ST_MEM instructions to write to
context data structures. This requires the following changes:
- verifier.c:do_check() for BPF_ST updated to:
- no longer forbid writes to registers of type PTR_TO_CTX;
- track dst_reg type in the env->insn_aux_data[...].ptr_type field
(same way it is done for BPF_STX and BPF_LDX instructions).
- verifier.c:convert_ctx_access() and various callbacks invoked by
it are updated to handle BPF_ST instruction alongside BPF_STX.
Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
kernel/bpf/cgroup.c | 49 ++++++++------
kernel/bpf/verifier.c | 79 +++++++++++-----------
net/core/filter.c | 72 ++++++++++----------
tools/testing/selftests/bpf/verifier/ctx.c | 11 ---
4 files changed, 108 insertions(+), 103 deletions(-)
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index bf2fdb33fb31..a57f1b44dc6c 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -2223,10 +2223,12 @@ static u32 sysctl_convert_ctx_access(enum bpf_access_type type,
BPF_FIELD_SIZEOF(struct bpf_sysctl_kern, ppos),
treg, si->dst_reg,
offsetof(struct bpf_sysctl_kern, ppos));
- *insn++ = BPF_STX_MEM(
- BPF_SIZEOF(u32), treg, si->src_reg,
+ *insn++ = BPF_RAW_INSN(
+ BPF_CLASS(si->code) | BPF_MEM | BPF_SIZEOF(u32),
+ treg, si->src_reg,
bpf_ctx_narrow_access_offset(
- 0, sizeof(u32), sizeof(loff_t)));
+ 0, sizeof(u32), sizeof(loff_t)),
+ si->imm);
*insn++ = BPF_LDX_MEM(
BPF_DW, treg, si->dst_reg,
offsetof(struct bpf_sysctl_kern, tmp_reg));
@@ -2376,10 +2378,17 @@ static bool cg_sockopt_is_valid_access(int off, int size,
return true;
}
-#define CG_SOCKOPT_ACCESS_FIELD(T, F) \
- T(BPF_FIELD_SIZEOF(struct bpf_sockopt_kern, F), \
- si->dst_reg, si->src_reg, \
- offsetof(struct bpf_sockopt_kern, F))
+#define CG_SOCKOPT_READ_FIELD(F) \
+ BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct bpf_sockopt_kern, F), \
+ si->dst_reg, si->src_reg, \
+ offsetof(struct bpf_sockopt_kern, F))
+
+#define CG_SOCKOPT_WRITE_FIELD(F) \
+ BPF_RAW_INSN((BPF_FIELD_SIZEOF(struct bpf_sockopt_kern, F) | \
+ BPF_MEM | BPF_CLASS(si->code)), \
+ si->dst_reg, si->src_reg, \
+ offsetof(struct bpf_sockopt_kern, F), \
+ si->imm)
static u32 cg_sockopt_convert_ctx_access(enum bpf_access_type type,
const struct bpf_insn *si,
@@ -2391,25 +2400,25 @@ static u32 cg_sockopt_convert_ctx_access(enum bpf_access_type type,
switch (si->off) {
case offsetof(struct bpf_sockopt, sk):
- *insn++ = CG_SOCKOPT_ACCESS_FIELD(BPF_LDX_MEM, sk);
+ *insn++ = CG_SOCKOPT_READ_FIELD(sk);
break;
case offsetof(struct bpf_sockopt, level):
if (type == BPF_WRITE)
- *insn++ = CG_SOCKOPT_ACCESS_FIELD(BPF_STX_MEM, level);
+ *insn++ = CG_SOCKOPT_WRITE_FIELD(level);
else
- *insn++ = CG_SOCKOPT_ACCESS_FIELD(BPF_LDX_MEM, level);
+ *insn++ = CG_SOCKOPT_READ_FIELD(level);
break;
case offsetof(struct bpf_sockopt, optname):
if (type == BPF_WRITE)
- *insn++ = CG_SOCKOPT_ACCESS_FIELD(BPF_STX_MEM, optname);
+ *insn++ = CG_SOCKOPT_WRITE_FIELD(optname);
else
- *insn++ = CG_SOCKOPT_ACCESS_FIELD(BPF_LDX_MEM, optname);
+ *insn++ = CG_SOCKOPT_READ_FIELD(optname);
break;
case offsetof(struct bpf_sockopt, optlen):
if (type == BPF_WRITE)
- *insn++ = CG_SOCKOPT_ACCESS_FIELD(BPF_STX_MEM, optlen);
+ *insn++ = CG_SOCKOPT_WRITE_FIELD(optlen);
else
- *insn++ = CG_SOCKOPT_ACCESS_FIELD(BPF_LDX_MEM, optlen);
+ *insn++ = CG_SOCKOPT_READ_FIELD(optlen);
break;
case offsetof(struct bpf_sockopt, retval):
BUILD_BUG_ON(offsetof(struct bpf_cg_run_ctx, run_ctx) != 0);
@@ -2429,9 +2438,11 @@ static u32 cg_sockopt_convert_ctx_access(enum bpf_access_type type,
*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct task_struct, bpf_ctx),
treg, treg,
offsetof(struct task_struct, bpf_ctx));
- *insn++ = BPF_STX_MEM(BPF_FIELD_SIZEOF(struct bpf_cg_run_ctx, retval),
- treg, si->src_reg,
- offsetof(struct bpf_cg_run_ctx, retval));
+ *insn++ = BPF_RAW_INSN(BPF_CLASS(si->code) | BPF_MEM |
+ BPF_FIELD_SIZEOF(struct bpf_cg_run_ctx, retval),
+ treg, si->src_reg,
+ offsetof(struct bpf_cg_run_ctx, retval),
+ si->imm);
*insn++ = BPF_LDX_MEM(BPF_DW, treg, si->dst_reg,
offsetof(struct bpf_sockopt_kern, tmp_reg));
} else {
@@ -2447,10 +2458,10 @@ static u32 cg_sockopt_convert_ctx_access(enum bpf_access_type type,
}
break;
case offsetof(struct bpf_sockopt, optval):
- *insn++ = CG_SOCKOPT_ACCESS_FIELD(BPF_LDX_MEM, optval);
+ *insn++ = CG_SOCKOPT_READ_FIELD(optval);
break;
case offsetof(struct bpf_sockopt, optval_end):
- *insn++ = CG_SOCKOPT_ACCESS_FIELD(BPF_LDX_MEM, optval_end);
+ *insn++ = CG_SOCKOPT_READ_FIELD(optval_end);
break;
}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 585edea642e1..be7d8df7257d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -13742,6 +13742,31 @@ static bool reg_type_mismatch(enum bpf_reg_type src, enum bpf_reg_type prev)
!reg_type_mismatch_ok(prev));
}
+static int save_aux_ptr_type(struct bpf_verifier_env *env, enum bpf_reg_type type)
+{
+ enum bpf_reg_type *prev_type = &env->insn_aux_data[env->insn_idx].ptr_type;
+
+ if (*prev_type == NOT_INIT) {
+ /* Saw a valid insn
+ * dst_reg = *(u32 *)(src_reg + off)
+ * save type to validate intersecting paths
+ */
+ *prev_type = type;
+ } else if (reg_type_mismatch(type, *prev_type)) {
+ /* Abuser program is trying to use the same insn
+ * dst_reg = *(u32*) (src_reg + off)
+ * with different pointer types:
+ * src_reg == ctx in one branch and
+ * src_reg == stack|map in some other branch.
+ * Reject it.
+ */
+ verbose(env, "same insn cannot be used with different pointers\n");
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
static int do_check(struct bpf_verifier_env *env)
{
bool pop_log = !(env->log.level & BPF_LOG_LEVEL2);
@@ -13851,7 +13876,7 @@ static int do_check(struct bpf_verifier_env *env)
return err;
} else if (class == BPF_LDX) {
- enum bpf_reg_type *prev_src_type, src_reg_type;
+ enum bpf_reg_type src_reg_type;
/* check for reserved fields is already done */
@@ -13875,29 +13900,11 @@ static int do_check(struct bpf_verifier_env *env)
if (err)
return err;
- prev_src_type = &env->insn_aux_data[env->insn_idx].ptr_type;
-
- if (*prev_src_type == NOT_INIT) {
- /* saw a valid insn
- * dst_reg = *(u32 *)(src_reg + off)
- * save type to validate intersecting paths
- */
- *prev_src_type = src_reg_type;
-
- } else if (reg_type_mismatch(src_reg_type, *prev_src_type)) {
- /* ABuser program is trying to use the same insn
- * dst_reg = *(u32*) (src_reg + off)
- * with different pointer types:
- * src_reg == ctx in one branch and
- * src_reg == stack|map in some other branch.
- * Reject it.
- */
- verbose(env, "same insn cannot be used with different pointers\n");
- return -EINVAL;
- }
-
+ err = save_aux_ptr_type(env, src_reg_type);
+ if (err)
+ return err;
} else if (class == BPF_STX) {
- enum bpf_reg_type *prev_dst_type, dst_reg_type;
+ enum bpf_reg_type dst_reg_type;
if (BPF_MODE(insn->code) == BPF_ATOMIC) {
err = check_atomic(env, env->insn_idx, insn);
@@ -13930,16 +13937,12 @@ static int do_check(struct bpf_verifier_env *env)
if (err)
return err;
- prev_dst_type = &env->insn_aux_data[env->insn_idx].ptr_type;
-
- if (*prev_dst_type == NOT_INIT) {
- *prev_dst_type = dst_reg_type;
- } else if (reg_type_mismatch(dst_reg_type, *prev_dst_type)) {
- verbose(env, "same insn cannot be used with different pointers\n");
- return -EINVAL;
- }
-
+ err = save_aux_ptr_type(env, dst_reg_type);
+ if (err)
+ return err;
} else if (class == BPF_ST) {
+ enum bpf_reg_type dst_reg_type;
+
if (BPF_MODE(insn->code) != BPF_MEM ||
insn->src_reg != BPF_REG_0) {
verbose(env, "BPF_ST uses reserved fields\n");
@@ -13950,12 +13953,7 @@ static int do_check(struct bpf_verifier_env *env)
if (err)
return err;
- if (is_ctx_reg(env, insn->dst_reg)) {
- verbose(env, "BPF_ST stores into R%d %s is not allowed\n",
- insn->dst_reg,
- reg_type_str(env, reg_state(env, insn->dst_reg)->type));
- return -EACCES;
- }
+ dst_reg_type = regs[insn->dst_reg].type;
/* check that memory (dst_reg + off) is writeable */
err = check_mem_access(env, env->insn_idx, insn->dst_reg,
@@ -13964,6 +13962,9 @@ static int do_check(struct bpf_verifier_env *env)
if (err)
return err;
+ err = save_aux_ptr_type(env, dst_reg_type);
+ if (err)
+ return err;
} else if (class == BPF_JMP || class == BPF_JMP32) {
u8 opcode = BPF_OP(insn->code);
@@ -15087,7 +15088,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
insn->code == (BPF_ST | BPF_MEM | BPF_W) ||
insn->code == (BPF_ST | BPF_MEM | BPF_DW)) {
type = BPF_WRITE;
- ctx_access = BPF_CLASS(insn->code) == BPF_STX;
+ ctx_access = true;
} else {
continue;
}
diff --git a/net/core/filter.c b/net/core/filter.c
index c746e4d77214..1353bb1d476a 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -9221,11 +9221,15 @@ static struct bpf_insn *bpf_convert_tstamp_write(const struct bpf_prog *prog,
#endif
/* <store>: skb->tstamp = tstamp */
- *insn++ = BPF_STX_MEM(BPF_DW, skb_reg, value_reg,
- offsetof(struct sk_buff, tstamp));
+ *insn++ = BPF_RAW_INSN(BPF_CLASS(si->code) | BPF_DW | BPF_MEM,
+ skb_reg, value_reg, offsetof(struct sk_buff, tstamp), si->imm);
return insn;
}
+#define BPF_COPY_STORE(size, si, off) \
+ BPF_RAW_INSN((si)->code | (size) | BPF_MEM, \
+ (si)->dst_reg, (si)->src_reg, (off), (si)->imm)
+
static u32 bpf_convert_ctx_access(enum bpf_access_type type,
const struct bpf_insn *si,
struct bpf_insn *insn_buf,
@@ -9255,9 +9259,9 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
case offsetof(struct __sk_buff, priority):
if (type == BPF_WRITE)
- *insn++ = BPF_STX_MEM(BPF_W, si->dst_reg, si->src_reg,
- bpf_target_off(struct sk_buff, priority, 4,
- target_size));
+ *insn++ = BPF_COPY_STORE(BPF_W, si,
+ bpf_target_off(struct sk_buff, priority, 4,
+ target_size));
else
*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg,
bpf_target_off(struct sk_buff, priority, 4,
@@ -9288,9 +9292,9 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
case offsetof(struct __sk_buff, mark):
if (type == BPF_WRITE)
- *insn++ = BPF_STX_MEM(BPF_W, si->dst_reg, si->src_reg,
- bpf_target_off(struct sk_buff, mark, 4,
- target_size));
+ *insn++ = BPF_COPY_STORE(BPF_W, si,
+ bpf_target_off(struct sk_buff, mark, 4,
+ target_size));
else
*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg,
bpf_target_off(struct sk_buff, mark, 4,
@@ -9310,10 +9314,10 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
case offsetof(struct __sk_buff, queue_mapping):
if (type == BPF_WRITE) {
*insn++ = BPF_JMP_IMM(BPF_JGE, si->src_reg, NO_QUEUE_MAPPING, 1);
- *insn++ = BPF_STX_MEM(BPF_H, si->dst_reg, si->src_reg,
- bpf_target_off(struct sk_buff,
- queue_mapping,
- 2, target_size));
+ *insn++ = BPF_COPY_STORE(BPF_H, si,
+ bpf_target_off(struct sk_buff,
+ queue_mapping,
+ 2, target_size));
} else {
*insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->src_reg,
bpf_target_off(struct sk_buff,
@@ -9349,8 +9353,7 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
off += offsetof(struct sk_buff, cb);
off += offsetof(struct qdisc_skb_cb, data);
if (type == BPF_WRITE)
- *insn++ = BPF_STX_MEM(BPF_SIZE(si->code), si->dst_reg,
- si->src_reg, off);
+ *insn++ = BPF_COPY_STORE(BPF_SIZE(si->code), si, off);
else
*insn++ = BPF_LDX_MEM(BPF_SIZE(si->code), si->dst_reg,
si->src_reg, off);
@@ -9365,8 +9368,7 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
off += offsetof(struct qdisc_skb_cb, tc_classid);
*target_size = 2;
if (type == BPF_WRITE)
- *insn++ = BPF_STX_MEM(BPF_H, si->dst_reg,
- si->src_reg, off);
+ *insn++ = BPF_COPY_STORE(BPF_H, si, off);
else
*insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg,
si->src_reg, off);
@@ -9399,9 +9401,9 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
case offsetof(struct __sk_buff, tc_index):
#ifdef CONFIG_NET_SCHED
if (type == BPF_WRITE)
- *insn++ = BPF_STX_MEM(BPF_H, si->dst_reg, si->src_reg,
- bpf_target_off(struct sk_buff, tc_index, 2,
- target_size));
+ *insn++ = BPF_COPY_STORE(BPF_H, si,
+ bpf_target_off(struct sk_buff, tc_index, 2,
+ target_size));
else
*insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->src_reg,
bpf_target_off(struct sk_buff, tc_index, 2,
@@ -9602,8 +9604,8 @@ u32 bpf_sock_convert_ctx_access(enum bpf_access_type type,
BUILD_BUG_ON(sizeof_field(struct sock, sk_bound_dev_if) != 4);
if (type == BPF_WRITE)
- *insn++ = BPF_STX_MEM(BPF_W, si->dst_reg, si->src_reg,
- offsetof(struct sock, sk_bound_dev_if));
+ *insn++ = BPF_COPY_STORE(BPF_W, si,
+ offsetof(struct sock, sk_bound_dev_if));
else
*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg,
offsetof(struct sock, sk_bound_dev_if));
@@ -9613,8 +9615,8 @@ u32 bpf_sock_convert_ctx_access(enum bpf_access_type type,
BUILD_BUG_ON(sizeof_field(struct sock, sk_mark) != 4);
if (type == BPF_WRITE)
- *insn++ = BPF_STX_MEM(BPF_W, si->dst_reg, si->src_reg,
- offsetof(struct sock, sk_mark));
+ *insn++ = BPF_COPY_STORE(BPF_W, si,
+ offsetof(struct sock, sk_mark));
else
*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg,
offsetof(struct sock, sk_mark));
@@ -9624,8 +9626,8 @@ u32 bpf_sock_convert_ctx_access(enum bpf_access_type type,
BUILD_BUG_ON(sizeof_field(struct sock, sk_priority) != 4);
if (type == BPF_WRITE)
- *insn++ = BPF_STX_MEM(BPF_W, si->dst_reg, si->src_reg,
- offsetof(struct sock, sk_priority));
+ *insn++ = BPF_COPY_STORE(BPF_W, si,
+ offsetof(struct sock, sk_priority));
else
*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg,
offsetof(struct sock, sk_priority));
@@ -9890,10 +9892,12 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type,
offsetof(S, TF)); \
*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(S, F), tmp_reg, \
si->dst_reg, offsetof(S, F)); \
- *insn++ = BPF_STX_MEM(SIZE, tmp_reg, si->src_reg, \
+ *insn++ = BPF_RAW_INSN(SIZE | BPF_MEM | BPF_CLASS(si->code), \
+ tmp_reg, si->src_reg, \
bpf_target_off(NS, NF, sizeof_field(NS, NF), \
target_size) \
- + OFF); \
+ + OFF, \
+ si->imm); \
*insn++ = BPF_LDX_MEM(BPF_DW, tmp_reg, si->dst_reg, \
offsetof(S, TF)); \
} while (0)
@@ -10128,9 +10132,11 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
struct bpf_sock_ops_kern, sk),\
reg, si->dst_reg, \
offsetof(struct bpf_sock_ops_kern, sk));\
- *insn++ = BPF_STX_MEM(BPF_FIELD_SIZEOF(OBJ, OBJ_FIELD), \
- reg, si->src_reg, \
- offsetof(OBJ, OBJ_FIELD)); \
+ *insn++ = BPF_RAW_INSN(BPF_FIELD_SIZEOF(OBJ, OBJ_FIELD) | \
+ BPF_MEM | BPF_CLASS(si->code), \
+ reg, si->src_reg, \
+ offsetof(OBJ, OBJ_FIELD), \
+ si->imm); \
*insn++ = BPF_LDX_MEM(BPF_DW, reg, si->dst_reg, \
offsetof(struct bpf_sock_ops_kern, \
temp)); \
@@ -10165,8 +10171,7 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
off -= offsetof(struct bpf_sock_ops, replylong[0]);
off += offsetof(struct bpf_sock_ops_kern, replylong[0]);
if (type == BPF_WRITE)
- *insn++ = BPF_STX_MEM(BPF_W, si->dst_reg, si->src_reg,
- off);
+ *insn++ = BPF_COPY_STORE(BPF_W, si, off);
else
*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg,
off);
@@ -10523,8 +10528,7 @@ static u32 sk_skb_convert_ctx_access(enum bpf_access_type type,
off += offsetof(struct sk_buff, cb);
off += offsetof(struct sk_skb_cb, data);
if (type == BPF_WRITE)
- *insn++ = BPF_STX_MEM(BPF_SIZE(si->code), si->dst_reg,
- si->src_reg, off);
+ *insn++ = BPF_COPY_STORE(BPF_SIZE(si->code), si, off);
else
*insn++ = BPF_LDX_MEM(BPF_SIZE(si->code), si->dst_reg,
si->src_reg, off);
diff --git a/tools/testing/selftests/bpf/verifier/ctx.c b/tools/testing/selftests/bpf/verifier/ctx.c
index c8eaf0536c24..2fd31612c0b8 100644
--- a/tools/testing/selftests/bpf/verifier/ctx.c
+++ b/tools/testing/selftests/bpf/verifier/ctx.c
@@ -1,14 +1,3 @@
-{
- "context stores via ST",
- .insns = {
- BPF_MOV64_IMM(BPF_REG_0, 0),
- BPF_ST_MEM(BPF_DW, BPF_REG_1, offsetof(struct __sk_buff, mark), 0),
- BPF_EXIT_INSN(),
- },
- .errstr = "BPF_ST stores into R1 ctx is not allowed",
- .result = REJECT,
- .prog_type = BPF_PROG_TYPE_SCHED_CLS,
-},
{
"context stores via BPF_ATOMIC",
.insns = {
--
2.39.0
