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@kernel.org>
---
 kernel/bpf/verifier.c | 25 ++++++----------------
 net/core/filter.c     | 49 +++++++++++++++++++++++++++++++++++++++----
 2 files changed, 51 insertions(+), 23 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2188b6674266..55e710e318e5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c

@@ -11750,6 +11750,7 @@ 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,

@@ -11785,6 +11786,7 @@ 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)

@@ -11816,10 +11818,12 @@ 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)

@@ -12741,7 +12745,8 @@ 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;

@@ -20898,9 +20903,7 @@ 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);

@@ -20910,22 +20913,6 @@ 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 2ec162dd83c4..6416689e3976 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c

@@ -12062,10 +12062,8 @@ __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;

@@ -12079,10 +12077,16 @@ 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)

@@ -12095,9 +12099,46 @@ 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: