[PATCH v6 bpf-next 5/7] bpf: Use btf_kfunc_id_set.remap logic for bpf_dynptr_from_skb

[Song Liu]

btf_kfunc_id_set.remap can pick proper version of a kfunc for the calling
context. Use this logic to select bpf_dynptr_from_skb or
bpf_dynptr_from_skb_rdonly. This will make the verifier simpler.

Unfortunately, btf_kfunc_id_set.remap cannot cover the DYNPTR_TYPE_SKB
logic in check_kfunc_args(). This can be addressed later.

Signed-off-by: Song Liu <song at kernel.org>
---
 kernel/bpf/verifier.c | 28 ++++++++-----------------
 net/core/filter.c     | 49 +++++++++++++++++++++++++++++++++++++++----
 2 files changed, 54 insertions(+), 23 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a5b02a8665f9..714918625e9f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11682,6 +11682,7 @@ enum special_kfunc_type {
 	KF_bpf_rbtree_add_impl,
 	KF_bpf_rbtree_first,
 	KF_bpf_dynptr_from_skb,
+	KF_bpf_dynptr_from_skb_rdonly,
 	KF_bpf_dynptr_from_xdp,
 	KF_bpf_dynptr_slice,
 	KF_bpf_dynptr_slice_rdwr,
@@ -11714,6 +11715,7 @@ BTF_ID(func, bpf_rbtree_add_impl)
 BTF_ID(func, bpf_rbtree_first)
 #ifdef CONFIG_NET
 BTF_ID(func, bpf_dynptr_from_skb)
+BTF_ID(func, bpf_dynptr_from_skb_rdonly)
 BTF_ID(func, bpf_dynptr_from_xdp)
 #endif
 BTF_ID(func, bpf_dynptr_slice)
@@ -11745,7 +11747,12 @@ BTF_ID(func, bpf_rbtree_add_impl)
 BTF_ID(func, bpf_rbtree_first)
 #ifdef CONFIG_NET
 BTF_ID(func, bpf_dynptr_from_skb)
+BTF_ID(func, bpf_dynptr_from_skb_rdonly)
 BTF_ID(func, bpf_dynptr_from_xdp)
+#else
+BTF_ID_UNUSED
+BTF_ID_UNUSED
+BTF_ID_UNUSED
 #endif
 BTF_ID(func, bpf_dynptr_slice)
 BTF_ID(func, bpf_dynptr_slice_rdwr)
@@ -12652,7 +12659,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 			if (is_kfunc_arg_uninit(btf, &args[i]))
 				dynptr_arg_type |= MEM_UNINIT;
 
-			if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb]) {
+			if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb] ||
+			    meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb_rdonly]) {
 				dynptr_arg_type |= DYNPTR_TYPE_SKB;
 			} else if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_xdp]) {
 				dynptr_arg_type |= DYNPTR_TYPE_XDP;
@@ -20813,9 +20821,7 @@ static void specialize_kfunc(struct bpf_verifier_env *env,
 			     u32 func_id, u16 offset, unsigned long *addr)
 {
 	struct bpf_prog *prog = env->prog;
-	bool seen_direct_write;
 	void *xdp_kfunc;
-	bool is_rdonly;
 
 	if (bpf_dev_bound_kfunc_id(func_id)) {
 		xdp_kfunc = bpf_dev_bound_resolve_kfunc(prog, func_id);
@@ -20825,22 +20831,6 @@ static void specialize_kfunc(struct bpf_verifier_env *env,
 		}
 		/* fallback to default kfunc when not supported by netdev */
 	}
-
-	if (offset)
-		return;
-
-	if (func_id == special_kfunc_list[KF_bpf_dynptr_from_skb]) {
-		seen_direct_write = env->seen_direct_write;
-		is_rdonly = !may_access_direct_pkt_data(env, NULL, BPF_WRITE);
-
-		if (is_rdonly)
-			*addr = (unsigned long)bpf_dynptr_from_skb_rdonly;
-
-		/* restore env->seen_direct_write to its original value, since
-		 * may_access_direct_pkt_data mutates it
-		 */
-		env->seen_direct_write = seen_direct_write;
-	}
 }
 
 static void __fixup_collection_insert_kfunc(struct bpf_insn_aux_data *insn_aux,
diff --git a/net/core/filter.c b/net/core/filter.c
index 21131ec25f24..f12bcc1b21d1 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -12047,10 +12047,8 @@ __bpf_kfunc int bpf_sk_assign_tcp_reqsk(struct __sk_buff *s, struct sock *sk,
 #endif
 }
 
-__bpf_kfunc_end_defs();
-
-int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
-			       struct bpf_dynptr *ptr__uninit)
+__bpf_kfunc int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
+					   struct bpf_dynptr *ptr__uninit)
 {
 	struct bpf_dynptr_kern *ptr = (struct bpf_dynptr_kern *)ptr__uninit;
 	int err;
@@ -12064,10 +12062,16 @@ int bpf_dynptr_from_skb_rdonly(struct __sk_buff *skb, u64 flags,
 	return 0;
 }
 
+__bpf_kfunc_end_defs();
+
 BTF_KFUNCS_START(bpf_kfunc_check_set_skb)
 BTF_ID_FLAGS(func, bpf_dynptr_from_skb, KF_TRUSTED_ARGS)
 BTF_KFUNCS_END(bpf_kfunc_check_set_skb)
 
+BTF_HIDDEN_KFUNCS_START(bpf_kfunc_check_hidden_set_skb)
+BTF_ID_FLAGS(func, bpf_dynptr_from_skb_rdonly, KF_TRUSTED_ARGS)
+BTF_KFUNCS_END(bpf_kfunc_check_hidden_set_skb)
+
 BTF_KFUNCS_START(bpf_kfunc_check_set_xdp)
 BTF_ID_FLAGS(func, bpf_dynptr_from_xdp)
 BTF_KFUNCS_END(bpf_kfunc_check_set_xdp)
@@ -12080,9 +12084,46 @@ BTF_KFUNCS_START(bpf_kfunc_check_set_tcp_reqsk)
 BTF_ID_FLAGS(func, bpf_sk_assign_tcp_reqsk, KF_TRUSTED_ARGS)
 BTF_KFUNCS_END(bpf_kfunc_check_set_tcp_reqsk)
 
+BTF_ID_LIST(bpf_dynptr_from_skb_list)
+BTF_ID(func, bpf_dynptr_from_skb)
+BTF_ID(func, bpf_dynptr_from_skb_rdonly)
+
+static u32 bpf_kfunc_set_skb_remap(const struct bpf_prog *prog, u32 kfunc_id)
+{
+	if (kfunc_id != bpf_dynptr_from_skb_list[0])
+		return 0;
+
+	switch (resolve_prog_type(prog)) {
+	/* Program types only with direct read access go here! */
+	case BPF_PROG_TYPE_LWT_IN:
+	case BPF_PROG_TYPE_LWT_OUT:
+	case BPF_PROG_TYPE_LWT_SEG6LOCAL:
+	case BPF_PROG_TYPE_SK_REUSEPORT:
+	case BPF_PROG_TYPE_FLOW_DISSECTOR:
+	case BPF_PROG_TYPE_CGROUP_SKB:
+		return bpf_dynptr_from_skb_list[1];
+
+	/* Program types with direct read + write access go here! */
+	case BPF_PROG_TYPE_SCHED_CLS:
+	case BPF_PROG_TYPE_SCHED_ACT:
+	case BPF_PROG_TYPE_XDP:
+	case BPF_PROG_TYPE_LWT_XMIT:
+	case BPF_PROG_TYPE_SK_SKB:
+	case BPF_PROG_TYPE_SK_MSG:
+	case BPF_PROG_TYPE_CGROUP_SOCKOPT:
+		return kfunc_id;
+
+	default:
+		break;
+	}
+	return bpf_dynptr_from_skb_list[1];
+}
+
 static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
 	.owner = THIS_MODULE,
 	.set = &bpf_kfunc_check_set_skb,
+	.hidden_set = &bpf_kfunc_check_hidden_set_skb,
+	.remap = &bpf_kfunc_set_skb_remap,
 };
 
 static const struct btf_kfunc_id_set bpf_kfunc_set_xdp = {
-- 
2.43.5