linux-kernel - [PATCH bpf-next 1/3] bpf: consider CONST_PTR_TO_MAP as trusted pointer to struct bpf

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Date:   Fri, 14 Jul 2023 14:20:58 +0000
From:   Anton Protopopov <aspsk@...valent.com>
To:     Martin KaFai Lau <martin.lau@...ux.dev>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
        Hou Tao <houtao1@...wei.com>, Joe Stringer <joe@...valent.com>,
        Anton Protopopov <aspsk@...valent.com>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: [PATCH bpf-next 1/3] bpf: consider CONST_PTR_TO_MAP as trusted pointer to struct bpf_map

Patch verifier to regard values of type CONST_PTR_TO_MAP as trusted
pointers to struct bpf_map. This allows kfuncs to work with `struct
bpf_map *` arguments.

Save some bytes by defining btf_bpf_map_id as BTF_ID_LIST_GLOBAL_SINGLE
(which is u32[1]), not as BTF_ID_LIST (which is u32[64]).

Signed-off-by: Anton Protopopov <aspsk@...valent.com>
---
 include/linux/btf_ids.h | 1 +
 kernel/bpf/map_iter.c   | 3 +--
 kernel/bpf/verifier.c   | 5 ++++-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
index 00950cc03bff..a3462a9b8e18 100644
--- a/include/linux/btf_ids.h
+++ b/include/linux/btf_ids.h
@@ -267,5 +267,6 @@ MAX_BTF_TRACING_TYPE,
 extern u32 btf_tracing_ids[];
 extern u32 bpf_cgroup_btf_id[];
 extern u32 bpf_local_storage_map_btf_id[];
+extern u32 btf_bpf_map_id[];
 
 #endif
diff --git a/kernel/bpf/map_iter.c b/kernel/bpf/map_iter.c
index d06d3b7150e5..b67996147895 100644
--- a/kernel/bpf/map_iter.c
+++ b/kernel/bpf/map_iter.c
@@ -78,8 +78,7 @@ static const struct seq_operations bpf_map_seq_ops = {
 	.show	= bpf_map_seq_show,
 };
 
-BTF_ID_LIST(btf_bpf_map_id)
-BTF_ID(struct, bpf_map)
+BTF_ID_LIST_GLOBAL_SINGLE(btf_bpf_map_id, struct, bpf_map)
 
 static const struct bpf_iter_seq_info bpf_map_seq_info = {
 	.seq_ops		= &bpf_map_seq_ops,
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0b9da95331d7..5663f97ef292 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5419,6 +5419,9 @@ static bool is_trusted_reg(const struct bpf_reg_state *reg)
 	if (reg->ref_obj_id)
 		return true;
 
+	if (reg->type == CONST_PTR_TO_MAP)
+		return true;
+
 	/* If a register is not referenced, it is trusted if it has the
 	 * MEM_ALLOC or PTR_TRUSTED type modifiers, and no others. Some of the
 	 * other type modifiers may be safe, but we elect to take an opt-in
@@ -10052,13 +10055,13 @@ static bool __btf_type_is_scalar_struct(struct bpf_verifier_env *env,
 	return true;
 }
 
-
 static u32 *reg2btf_ids[__BPF_REG_TYPE_MAX] = {
 #ifdef CONFIG_NET
 	[PTR_TO_SOCKET] = &btf_sock_ids[BTF_SOCK_TYPE_SOCK],
 	[PTR_TO_SOCK_COMMON] = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
 	[PTR_TO_TCP_SOCK] = &btf_sock_ids[BTF_SOCK_TYPE_TCP],
 #endif
+	[CONST_PTR_TO_MAP] = btf_bpf_map_id,
 };
 
 enum kfunc_ptr_arg_type {
-- 
2.34.1