Merge branch 'bpf-dynamic-relinking'

Alexei Starovoitov says:

====================
The last few month BPF community has been discussing an approach to call
chaining, since exiting bpt_tail_call() mechanism used in production XDP
programs has plenty of downsides. The outcome of these discussion was a
conclusion to implement dynamic re-linking of BPF programs. Where rootlet XDP
program attached to a netdevice can programmatically define a policy of
execution of other XDP programs. Such rootlet would be compiled as normal XDP
program and provide a number of placeholder global functions which later can be
replaced with future XDP programs. BPF trampoline, function by function
verification were building blocks towards that goal. The patch 1 is a final
building block. It introduces dynamic program extensions. A number of
improvements like more flexible function by function verification and better
libbpf api will be implemented in future patches.

v1->v2:
- addressed Andrii's comments
- rebase
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

4 files changed, 17 insertions, 1 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 8e3b8f4ad183..05d16615054c 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -465,7 +465,8 @@ void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start);
 enum bpf_tramp_prog_type {
 	BPF_TRAMP_FENTRY,
 	BPF_TRAMP_FEXIT,
-	BPF_TRAMP_MAX
+	BPF_TRAMP_MAX,
+	BPF_TRAMP_REPLACE, /* more than MAX */
 };
 
 struct bpf_trampoline {
@@ -480,6 +481,11 @@ struct bpf_trampoline {
 		void *addr;
 		bool ftrace_managed;
 	} func;
+	/* if !NULL this is BPF_PROG_TYPE_EXT program that extends another BPF
+	 * program by replacing one of its functions. func.addr is the address
+	 * of the function it replaced.
+	 */
+	struct bpf_prog *extension_prog;
 	/* list of BPF programs using this trampoline */
 	struct hlist_head progs_hlist[BPF_TRAMP_MAX];
 	/* Number of attached programs. A counter per kind. */
@@ -1107,6 +1113,8 @@ int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
 			     struct bpf_reg_state *regs);
 int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
 			  struct bpf_reg_state *reg);
+int btf_check_type_match(struct bpf_verifier_env *env, struct bpf_prog *prog,
+			 struct btf *btf, const struct btf_type *t);
 
 struct bpf_prog *bpf_prog_by_id(u32 id);
 
diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
index 9f326e6ef885..c81d4ece79a4 100644
--- a/include/linux/bpf_types.h
+++ b/include/linux/bpf_types.h
@@ -68,6 +68,8 @@ BPF_PROG_TYPE(BPF_PROG_TYPE_SK_REUSEPORT, sk_reuseport,
 #if defined(CONFIG_BPF_JIT)
 BPF_PROG_TYPE(BPF_PROG_TYPE_STRUCT_OPS, bpf_struct_ops,
 	      void *, void *)
+BPF_PROG_TYPE(BPF_PROG_TYPE_EXT, bpf_extension,
+	      void *, void *)
 #endif
 
 BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY, array_map_ops)
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 881e9b76ef49..5c1ea99b480f 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -107,6 +107,11 @@ static inline u16 btf_type_vlen(const struct btf_type *t)
 	return BTF_INFO_VLEN(t->info);
 }
 
+static inline u16 btf_func_linkage(const struct btf_type *t)
+{
+	return BTF_INFO_VLEN(t->info);
+}
+
 static inline bool btf_type_kflag(const struct btf_type *t)
 {
 	return BTF_INFO_KFLAG(t->info);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 033d90a2282d..e81628eb059c 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -180,6 +180,7 @@ enum bpf_prog_type {
 	BPF_PROG_TYPE_CGROUP_SOCKOPT,
 	BPF_PROG_TYPE_TRACING,
 	BPF_PROG_TYPE_STRUCT_OPS,
+	BPF_PROG_TYPE_EXT,
 };
 
 enum bpf_attach_type {