[PATCH RFC bpf-next v1 3/6] bpf: Extend kfunc with PTR_TO_CTX and PTR_TO_MEM arguments

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Allow passing PTR_TO_CTX, if the kfunc expects a matching struct type,
and punt to ptr_to_mem block if reg->type does not fall in one BTF ID
types. This will be used by future commits to get access to XDP and TC
PTR_TO_CTX.

Also add a btf_mod module parameter, so that the kfunc_id's owner module
can be used in future commit adding reference tracking for
PTR_TO_BTF_ID.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/bpf.h   |  3 ++-
 kernel/bpf/btf.c      | 61 +++++++++++++++++++++----------------------
 kernel/bpf/verifier.c |  4 +--
 3 files changed, 34 insertions(+), 34 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 6deebf8bf78f..f8be80f748fc 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1665,7 +1665,8 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
 				struct bpf_reg_state *regs);
 int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
 			      const struct btf *btf, u32 func_id,
-			      struct bpf_reg_state *regs);
+			      struct bpf_reg_state *regs,
+			      struct module *btf_mod);
 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_log *log, const struct bpf_prog *prog,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 1773f91fff10..9099ef64b077 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -5566,7 +5566,8 @@ static u32 *reg2btf_ids[__BPF_REG_TYPE_MAX] = {
 static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 				    const struct btf *btf, u32 func_id,
 				    struct bpf_reg_state *regs,
-				    bool ptr_to_mem_ok)
+				    bool ptr_to_mem_ok,
+				    struct module *btf_mod)
 {
 	struct bpf_verifier_log *log = &env->log;
 	const char *func_name, *ref_tname;
@@ -5602,8 +5603,10 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 	 * verifier sees.
 	 */
 	for (i = 0; i < nargs; i++) {
+		const struct btf_type *resolve_ret;
 		u32 regno = i + 1;
 		struct bpf_reg_state *reg = &regs[regno];
+		u32 type_size;
 
 		t = btf_type_skip_modifiers(btf, args[i].type, NULL);
 		if (btf_type_is_scalar(t)) {
@@ -5621,19 +5624,25 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 
 		ref_t = btf_type_skip_modifiers(btf, t->type, &ref_id);
 		ref_tname = btf_name_by_offset(btf, ref_t->name_off);
-		if (btf_is_kernel(btf)) {
+		if (btf_get_prog_ctx_type(log, btf, t,
+					  env->prog->type, i)) {
+			/* If function expects ctx type in BTF check that caller
+			 * is passing PTR_TO_CTX.
+			 */
+			if (reg->type != PTR_TO_CTX) {
+				bpf_log(log,
+					"arg#%d expected pointer to ctx, but got %s\n",
+					i, btf_type_str(t));
+				return -EINVAL;
+			}
+			if (check_ctx_reg(env, reg, regno))
+				return -EINVAL;
+		} else if (btf_is_kernel(btf)) {
 			const struct btf_type *reg_ref_t;
 			const struct btf *reg_btf;
 			const char *reg_ref_tname;
 			u32 reg_ref_id;
 
-			if (!btf_type_is_struct(ref_t)) {
-				bpf_log(log, "kernel function %s args#%d pointer type %s %s is not supported\n",
-					func_name, i, btf_type_str(ref_t),
-					ref_tname);
-				return -EINVAL;
-			}
-
 			if (reg->type == PTR_TO_BTF_ID) {
 				reg_btf = reg->btf;
 				reg_ref_id = reg->btf_id;
@@ -5641,9 +5650,13 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 				reg_btf = btf_vmlinux;
 				reg_ref_id = *reg2btf_ids[reg->type];
 			} else {
-				bpf_log(log, "kernel function %s args#%d expected pointer to %s %s but R%d is not a pointer to btf_id\n",
-					func_name, i,
-					btf_type_str(ref_t), ref_tname, regno);
+				goto ptr_to_mem;
+			}
+
+			if (!btf_type_is_struct(ref_t)) {
+				bpf_log(log, "kernel function %s args#%d pointer type %s %s is not supported\n",
+					func_name, i, btf_type_str(ref_t),
+					ref_tname);
 				return -EINVAL;
 			}
 
@@ -5660,23 +5673,8 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 					reg_ref_tname);
 				return -EINVAL;
 			}
-		} else if (btf_get_prog_ctx_type(log, btf, t,
-						 env->prog->type, i)) {
-			/* If function expects ctx type in BTF check that caller
-			 * is passing PTR_TO_CTX.
-			 */
-			if (reg->type != PTR_TO_CTX) {
-				bpf_log(log,
-					"arg#%d expected pointer to ctx, but got %s\n",
-					i, btf_type_str(t));
-				return -EINVAL;
-			}
-			if (check_ctx_reg(env, reg, regno))
-				return -EINVAL;
 		} else if (ptr_to_mem_ok) {
-			const struct btf_type *resolve_ret;
-			u32 type_size;
-
+ptr_to_mem:
 			resolve_ret = btf_resolve_size(btf, ref_t, &type_size);
 			if (IS_ERR(resolve_ret)) {
 				bpf_log(log,
@@ -5723,7 +5721,7 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
 		return -EINVAL;
 
 	is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
-	err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global);
+	err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global, NULL);
 
 	/* Compiler optimizations can remove arguments from static functions
 	 * or mismatched type can be passed into a global function.
@@ -5736,9 +5734,10 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
 
 int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
 			      const struct btf *btf, u32 func_id,
-			      struct bpf_reg_state *regs)
+			      struct bpf_reg_state *regs,
+			      struct module *btf_mod)
 {
-	return btf_check_func_arg_match(env, btf, func_id, regs, false);
+	return btf_check_func_arg_match(env, btf, func_id, regs, false, btf_mod);
 }
 
 /* Convert BTF of a function into bpf_reg_state if possible
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3c8aa7df1773..ca4627f81b75 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6713,8 +6713,8 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn)
 	}
 
 	/* Check the arguments */
-	err = btf_check_kfunc_arg_match(env, desc_btf, func_id, regs);
-	if (err)
+	err = btf_check_kfunc_arg_match(env, desc_btf, func_id, regs, btf_mod);
+	if (err < 0)
 		return err;
 
 	for (i = 0; i < CALLER_SAVED_REGS; i++)
-- 
2.33.1