From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Date: Sat, 5 Mar 2022 04:16:38 +0530
Subject: bpf: Add check_func_arg_reg_off function
Patch-mainline: Queued in subsystem maintainer repository
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux
Git-commit: 25b35dd28138f61f9a0fb8b76c0483761fd228bd
References: git-fixes
X-Info: dependency for "bpf: Fix PTR_TO_BTF_ID var_off check" 655efe5089f077485eec848272bd7e26b1a5a735

Lift the list of register types allowed for having fixed and variable
offsets when passed as helper function arguments into a common helper,
so that they can be reused for kfunc checks in later commits. Keeping a
common helper aids maintainability and allows us to follow the same
consistent rules across helpers and kfuncs. Also, convert check_func_arg
to use this function.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220304224645.3677453-2-memxor@gmail.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 include/linux/bpf_verifier.h |    3 +
 kernel/bpf/verifier.c        |   69 +++++++++++++++++++++++++------------------
 2 files changed, 44 insertions(+), 28 deletions(-)

--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -521,6 +521,9 @@ bpf_prog_offload_remove_insns(struct bpf
 
 int check_ptr_off_reg(struct bpf_verifier_env *env,
 		      const struct bpf_reg_state *reg, int regno);
+int check_func_arg_reg_off(struct bpf_verifier_env *env,
+			   const struct bpf_reg_state *reg, int regno,
+			   enum bpf_arg_type arg_type);
 int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
 		   u32 regno, u32 mem_size);
 
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5264,6 +5264,44 @@ found:
 	return 0;
 }
 
+int check_func_arg_reg_off(struct bpf_verifier_env *env,
+			   const struct bpf_reg_state *reg, int regno,
+			   enum bpf_arg_type arg_type)
+{
+	enum bpf_reg_type type = reg->type;
+	bool fixed_off_ok = false;
+
+	switch ((u32)type) {
+	case SCALAR_VALUE:
+	/* Pointer types where reg offset is explicitly allowed: */
+	case PTR_TO_PACKET:
+	case PTR_TO_PACKET_META:
+	case PTR_TO_MAP_KEY:
+	case PTR_TO_MAP_VALUE:
+	case PTR_TO_MEM:
+	case PTR_TO_MEM | MEM_RDONLY:
+	case PTR_TO_MEM | MEM_ALLOC:
+	case PTR_TO_BUF:
+	case PTR_TO_BUF | MEM_RDONLY:
+	case PTR_TO_STACK:
+		/* Some of the argument types nevertheless require a
+		 * zero register offset.
+		 */
+		if (arg_type != ARG_PTR_TO_ALLOC_MEM)
+			return 0;
+		break;
+	/* All the rest must be rejected, except PTR_TO_BTF_ID which allows
+	 * fixed offset.
+	 */
+	case PTR_TO_BTF_ID:
+		fixed_off_ok = true;
+		break;
+	default:
+		break;
+	}
+	return __check_ptr_off_reg(env, reg, regno, fixed_off_ok);
+}
+
 static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 			  struct bpf_call_arg_meta *meta,
 			  const struct bpf_func_proto *fn)
@@ -5313,34 +5351,9 @@ static int check_func_arg(struct bpf_ver
 	if (err)
 		return err;
 
-	switch ((u32)type) {
-	case SCALAR_VALUE:
-	/* Pointer types where reg offset is explicitly allowed: */
-	case PTR_TO_PACKET:
-	case PTR_TO_PACKET_META:
-	case PTR_TO_MAP_KEY:
-	case PTR_TO_MAP_VALUE:
-	case PTR_TO_MEM:
-	case PTR_TO_MEM | MEM_RDONLY:
-	case PTR_TO_MEM | MEM_ALLOC:
-	case PTR_TO_BUF:
-	case PTR_TO_BUF | MEM_RDONLY:
-	case PTR_TO_STACK:
-		/* Some of the argument types nevertheless require a
-		 * zero register offset.
-		 */
-		if (arg_type == ARG_PTR_TO_ALLOC_MEM)
-			goto force_off_check;
-		break;
-	/* All the rest must be rejected: */
-	default:
-force_off_check:
-		err = __check_ptr_off_reg(env, reg, regno,
-					  type == PTR_TO_BTF_ID);
-		if (err < 0)
-			return err;
-		break;
-	}
+	err = check_func_arg_reg_off(env, reg, regno, arg_type);
+	if (err)
+		return err;
 
 skip_type_check:
 	if (reg->ref_obj_id) {