[PATCH bpf-next v2 1/2] bpf: Silence a warning in btf_type_id_size()

[PATCH bpf-next v2 1/2] bpf: Silence a warning in btf_type_id_size()

[Yonghong Song]

syzbot reported a warning in [1] with the following stacktrace:
  WARNING: CPU: 0 PID: 5005 at kernel/bpf/btf.c:1988 btf_type_id_size+0x2d9/0x9d0 kernel/bpf/btf.c:1988
  ...
  RIP: 0010:btf_type_id_size+0x2d9/0x9d0 kernel/bpf/btf.c:1988
  ...
  Call Trace:
   <TASK>
   map_check_btf kernel/bpf/syscall.c:1024 [inline]
   map_create+0x1157/0x1860 kernel/bpf/syscall.c:1198
   __sys_bpf+0x127f/0x5420 kernel/bpf/syscall.c:5040
   __do_sys_bpf kernel/bpf/syscall.c:5162 [inline]
   __se_sys_bpf kernel/bpf/syscall.c:5160 [inline]
   __x64_sys_bpf+0x79/0xc0 kernel/bpf/syscall.c:5160
   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
   do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
   entry_SYSCALL_64_after_hwframe+0x63/0xcd

With the following btf
  [1] DECL_TAG 'a' type_id=4 component_idx=-1
  [2] PTR '(anon)' type_id=0
  [3] TYPE_TAG 'a' type_id=2
  [4] VAR 'a' type_id=3, linkage=static
and when the bpf_attr.btf_key_type_id = 1 (DECL_TAG),
the following WARN_ON_ONCE in btf_type_id_size() is triggered:
  if (WARN_ON_ONCE(!btf_type_is_modifier(size_type) &&
                   !btf_type_is_var(size_type)))
          return NULL;

Note that 'return NULL' is the correct behavior as we don't want
a DECL_TAG type to be used as a btf_{key,value}_type_id even
for the case like 'DECL_TAG -> STRUCT'. So there
is no correctness issue here, we just want to silence warning.

To silence the warning, I added DECL_TAG as one of kinds in
btf_type_nosize() which will cause btf_type_id_size() returning
NULL earlier without the warning.

  [1] https://lore.kernel.org/bpf/000000000000e0df8d05fc75ba86@google.com/

Reported-by: syzbot+958967f249155967d42a@syzkaller.appspotmail.com
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 kernel/bpf/btf.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 947f0b83bfad..bd2cac057928 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -492,25 +492,26 @@ static bool btf_type_is_fwd(const struct btf_type *t)
 	return BTF_INFO_KIND(t->info) == BTF_KIND_FWD;
 }
 
-static bool btf_type_nosize(const struct btf_type *t)
+static bool btf_type_is_datasec(const struct btf_type *t)
 {
-	return btf_type_is_void(t) || btf_type_is_fwd(t) ||
-	       btf_type_is_func(t) || btf_type_is_func_proto(t);
+	return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;
 }
 
-static bool btf_type_nosize_or_null(const struct btf_type *t)
+static bool btf_type_is_decl_tag(const struct btf_type *t)
 {
-	return !t || btf_type_nosize(t);
+	return BTF_INFO_KIND(t->info) == BTF_KIND_DECL_TAG;
 }
 
-static bool btf_type_is_datasec(const struct btf_type *t)
+static bool btf_type_nosize(const struct btf_type *t)
 {
-	return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;
+	return btf_type_is_void(t) || btf_type_is_fwd(t) ||
+	       btf_type_is_func(t) || btf_type_is_func_proto(t) ||
+	       btf_type_is_decl_tag(t);
 }
 
-static bool btf_type_is_decl_tag(const struct btf_type *t)
+static bool btf_type_nosize_or_null(const struct btf_type *t)
 {
-	return BTF_INFO_KIND(t->info) == BTF_KIND_DECL_TAG;
+	return !t || btf_type_nosize(t);
 }
 
 static bool btf_type_is_decl_tag_target(const struct btf_type *t)
-- 
2.34.1

[PATCH bpf-next v2 2/2] selftests/bpf: Add a test where map key_type_id with decl_tag type

[Yonghong Song]

Add two selftests where map creation key/value type_id's are
decl_tags. Without previous patch, kernel warnings will
appear similar to the one in the previous patch. With the previous
patch, both kernel warnings are silenced.

Signed-off-by: Yonghong Song <yhs@fb.com>
---
 tools/testing/selftests/bpf/prog_tests/btf.c | 40 ++++++++++++++++++++
 1 file changed, 40 insertions(+)

Changelogs:
  v1 -> v2:
    . added both key and value types as decl_tag's.
    . updated commit message accordingly.


diff --git a/tools/testing/selftests/bpf/prog_tests/btf.c b/tools/testing/selftests/bpf/prog_tests/btf.c
index 210d643fda6c..4e0cdb593318 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf.c
@@ -3990,6 +3990,46 @@ static struct btf_raw_test raw_tests[] = {
 	.btf_load_err = true,
 	.err_str = "Invalid arg#1",
 },
+{
+	.descr = "decl_tag test #18, decl_tag as the map key type",
+	.raw_types = {
+		BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),	/* [1] */
+		BTF_STRUCT_ENC(0, 2, 8),			/* [2] */
+		BTF_MEMBER_ENC(NAME_TBD, 1, 0),
+		BTF_MEMBER_ENC(NAME_TBD, 1, 32),
+		BTF_DECL_TAG_ENC(NAME_TBD, 2, -1),		/* [3] */
+		BTF_END_RAW,
+	},
+	BTF_STR_SEC("\0m1\0m2\0tag"),
+	.map_type = BPF_MAP_TYPE_HASH,
+	.map_name = "tag_type_check_btf",
+	.key_size = 8,
+	.value_size = 4,
+	.key_type_id = 3,
+	.value_type_id = 1,
+	.max_entries = 1,
+	.map_create_err = true,
+},
+{
+	.descr = "decl_tag test #19, decl_tag as the map value type",
+	.raw_types = {
+		BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),	/* [1] */
+		BTF_STRUCT_ENC(0, 2, 8),			/* [2] */
+		BTF_MEMBER_ENC(NAME_TBD, 1, 0),
+		BTF_MEMBER_ENC(NAME_TBD, 1, 32),
+		BTF_DECL_TAG_ENC(NAME_TBD, 2, -1),		/* [3] */
+		BTF_END_RAW,
+	},
+	BTF_STR_SEC("\0m1\0m2\0tag"),
+	.map_type = BPF_MAP_TYPE_HASH,
+	.map_name = "tag_type_check_btf",
+	.key_size = 4,
+	.value_size = 8,
+	.key_type_id = 1,
+	.value_type_id = 3,
+	.max_entries = 1,
+	.map_create_err = true,
+},
 {
 	.descr = "type_tag test #1",
 	.raw_types = {
-- 
2.34.1

Re: [PATCH bpf-next v2 1/2] bpf: Silence a warning in btf_type_id_size()

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Martin KaFai Lau <martin.lau@kernel.org>:

On Tue, 30 May 2023 13:50:29 -0700 you wrote:
> syzbot reported a warning in [1] with the following stacktrace:
>   WARNING: CPU: 0 PID: 5005 at kernel/bpf/btf.c:1988 btf_type_id_size+0x2d9/0x9d0 kernel/bpf/btf.c:1988
>   ...
>   RIP: 0010:btf_type_id_size+0x2d9/0x9d0 kernel/bpf/btf.c:1988
>   ...
>   Call Trace:
>    <TASK>
>    map_check_btf kernel/bpf/syscall.c:1024 [inline]
>    map_create+0x1157/0x1860 kernel/bpf/syscall.c:1198
>    __sys_bpf+0x127f/0x5420 kernel/bpf/syscall.c:5040
>    __do_sys_bpf kernel/bpf/syscall.c:5162 [inline]
>    __se_sys_bpf kernel/bpf/syscall.c:5160 [inline]
>    __x64_sys_bpf+0x79/0xc0 kernel/bpf/syscall.c:5160
>    do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>    do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
>    entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> [...]

Here is the summary with links:
  - [bpf-next,v2,1/2] bpf: Silence a warning in btf_type_id_size()
    https://git.kernel.org/bpf/bpf-next/c/e6c2f594ed96
  - [bpf-next,v2,2/2] selftests/bpf: Add a test where map key_type_id with decl_tag type
    https://git.kernel.org/bpf/bpf-next/c/e38096d95f4d

You are awesome, thank you!
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