diff mbox series

[bpf-next,1/3] bpf: Check unsupported ops from the bpf_struct_ops's cfi_stubs

Message ID 20240720062233.2319723-2-martin.lau@linux.dev (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series bpf: Retire the unsupported_ops usage in struct_ops | expand

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netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit fail Errors and warnings before: 898 this patch: 899
netdev/build_tools success Errors and warnings before: 0 this patch: 0
netdev/cc_maintainers warning 13 maintainers not CCed: kpsingh@kernel.org haoluo@google.com edumazet@google.com kuba@kernel.org dsahern@kernel.org john.fastabend@gmail.com jolsa@kernel.org yonghong.song@linux.dev song@kernel.org eddyz87@gmail.com pabeni@redhat.com sdf@fomichev.me netdev@vger.kernel.org
netdev/build_clang success Errors and warnings before: 971 this patch: 971
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn fail Errors and warnings before: 7630 this patch: 7631
netdev/checkpatch warning CHECK: Please use a blank line after function/struct/union/enum declarations WARNING: ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP WARNING: line length of 87 exceeds 80 columns WARNING: line length of 89 exceeds 80 columns
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 6 this patch: 6
netdev/source_inline success Was 0 now: 0

Commit Message

Martin KaFai Lau July 20, 2024, 6:22 a.m. UTC 
From: Martin KaFai Lau <martin.lau@kernel.org>

The bpf_tcp_ca struct_ops currently uses a "u32 unsupported_ops[]"
array to track which ops is not supported.

After cfi_stubs had been added, the function pointer in cfi_stubs is
also NULL for the unsupported ops. Thus, the "u32 unsupported_ops[]"
becomes redundant. This observation was originally brought up in the
bpf/cfi discussion:
https://lore.kernel.org/bpf/CAADnVQJoEkdjyCEJRPASjBw1QGsKYrF33QdMGc1RZa9b88bAEA@mail.gmail.com/

The recent bpf qdisc patch (https://lore.kernel.org/bpf/20240714175130.4051012-6-amery.hung@bytedance.com/)
also needs to specify quite many unsupported ops. It is a good time
to clean it up.

This patch removes the need of "u32 unsupported_ops[]" and tests for null-ness
in the cfi_stubs instead.

Testing the cfi_stubs is done in a new function bpf_struct_ops_supported().
The verifier will call bpf_struct_ops_supported() when loading the
struct_ops program. The ".check_member" is removed from the bpf_tcp_ca
in this patch. ".check_member" could still be useful for other subsytems
to enforce other restrictions (e.g. sched_ext checks for prog->sleepable).

To keep the same error return, ENOTSUPP is used.

Cc: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
---
 include/linux/bpf.h         |  5 +++++
 kernel/bpf/bpf_struct_ops.c |  7 +++++++
 kernel/bpf/verifier.c       | 10 +++++++++-
 net/ipv4/bpf_tcp_ca.c       | 26 --------------------------
 4 files changed, 21 insertions(+), 27 deletions(-)

Comments

kernel test robot July 20, 2024, 2:45 p.m. UTC | #1 
Hi Martin,

kernel test robot noticed the following build warnings:

[auto build test WARNING on bpf-next/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Martin-KaFai-Lau/bpf-Check-unsupported-ops-from-the-bpf_struct_ops-s-cfi_stubs/20240720-144313
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
patch link:    https://lore.kernel.org/r/20240720062233.2319723-2-martin.lau%40linux.dev
patch subject: [PATCH bpf-next 1/3] bpf: Check unsupported ops from the bpf_struct_ops's cfi_stubs
config: i386-randconfig-001-20240720 (https://download.01.org/0day-ci/archive/20240720/202407202244.HvnUVyjM-lkp@intel.com/config)
compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240720/202407202244.HvnUVyjM-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202407202244.HvnUVyjM-lkp@intel.com/

All warnings (new ones prefixed by >>):

   kernel/bpf/bpf_struct_ops.c: In function 'bpf_struct_ops_supported':
>> kernel/bpf/bpf_struct_ops.c:1045:48: warning: dereferencing 'void *' pointer
     void *func_ptr = *(void **)(&st_ops->cfi_stubs[moff]);
                                                   ^


vim +1045 kernel/bpf/bpf_struct_ops.c

  1042	
  1043	int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff)
  1044	{
> 1045		void *func_ptr = *(void **)(&st_ops->cfi_stubs[moff]);
  1046	
  1047		return func_ptr ? 0 : -ENOTSUPP;
  1048	}
  1049
Amery Hung July 21, 2024, 10:45 p.m. UTC | #2 
On Sat, Jul 20, 2024 at 7:45 AM kernel test robot <lkp@intel.com> wrote:
>
> Hi Martin,
>
> kernel test robot noticed the following build warnings:
>
> [auto build test WARNING on bpf-next/master]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Martin-KaFai-Lau/bpf-Check-unsupported-ops-from-the-bpf_struct_ops-s-cfi_stubs/20240720-144313
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
> patch link:    https://lore.kernel.org/r/20240720062233.2319723-2-martin.lau%40linux.dev
> patch subject: [PATCH bpf-next 1/3] bpf: Check unsupported ops from the bpf_struct_ops's cfi_stubs
> config: i386-randconfig-001-20240720 (https://download.01.org/0day-ci/archive/20240720/202407202244.HvnUVyjM-lkp@intel.com/config)
> compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240720/202407202244.HvnUVyjM-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202407202244.HvnUVyjM-lkp@intel.com/
>
> All warnings (new ones prefixed by >>):
>
>    kernel/bpf/bpf_struct_ops.c: In function 'bpf_struct_ops_supported':
> >> kernel/bpf/bpf_struct_ops.c:1045:48: warning: dereferencing 'void *' pointer
>      void *func_ptr = *(void **)(&st_ops->cfi_stubs[moff]);
>                                                    ^
>
>
> vim +1045 kernel/bpf/bpf_struct_ops.c
>
>   1042
>   1043  int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff)
>   1044  {
> > 1045          void *func_ptr = *(void **)(&st_ops->cfi_stubs[moff]);

The compiler warning can be fixed with:
void *func_ptr = *(void **)(st_ops->cfi_stubs + moff);

The patch looks good to me. I tested it with bpf qdisc, and it does
what it is supposed to do by prohibiting users to attach to an
operator whose cfi stub is not defined.

Thanks,
Amery


>   1046
>   1047          return func_ptr ? 0 : -ENOTSUPP;
>   1048  }
>   1049
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
Martin KaFai Lau July 22, 2024, 5:34 p.m. UTC | #3 
On 7/21/24 3:45 PM, Amery Hung wrote:
> On Sat, Jul 20, 2024 at 7:45 AM kernel test robot <lkp@intel.com> wrote:
>>
>> Hi Martin,
>>
>> kernel test robot noticed the following build warnings:
>>
>> [auto build test WARNING on bpf-next/master]
>>
>> url:    https://github.com/intel-lab-lkp/linux/commits/Martin-KaFai-Lau/bpf-Check-unsupported-ops-from-the-bpf_struct_ops-s-cfi_stubs/20240720-144313
>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
>> patch link:    https://lore.kernel.org/r/20240720062233.2319723-2-martin.lau%40linux.dev
>> patch subject: [PATCH bpf-next 1/3] bpf: Check unsupported ops from the bpf_struct_ops's cfi_stubs
>> config: i386-randconfig-001-20240720 (https://download.01.org/0day-ci/archive/20240720/202407202244.HvnUVyjM-lkp@intel.com/config)
>> compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240720/202407202244.HvnUVyjM-lkp@intel.com/reproduce)
>>
>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>> the same patch/commit), kindly add following tags
>> | Reported-by: kernel test robot <lkp@intel.com>
>> | Closes: https://lore.kernel.org/oe-kbuild-all/202407202244.HvnUVyjM-lkp@intel.com/
>>
>> All warnings (new ones prefixed by >>):
>>
>>     kernel/bpf/bpf_struct_ops.c: In function 'bpf_struct_ops_supported':
>>>> kernel/bpf/bpf_struct_ops.c:1045:48: warning: dereferencing 'void *' pointer
>>       void *func_ptr = *(void **)(&st_ops->cfi_stubs[moff]);
>>                                                     ^
>>
>>
>> vim +1045 kernel/bpf/bpf_struct_ops.c
>>
>>    1042
>>    1043  int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff)
>>    1044  {
>>> 1045          void *func_ptr = *(void **)(&st_ops->cfi_stubs[moff]);
> 
> The compiler warning can be fixed with:
> void *func_ptr = *(void **)(st_ops->cfi_stubs + moff);
> 
> The patch looks good to me. I tested it with bpf qdisc, and it does
> what it is supposed to do by prohibiting users to attach to an
> operator whose cfi stub is not defined.

Thanks for testing. I just tried gcc and can repro it. I will respin.
diff mbox series

Patch

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 4f1d4a97b9d1..6464dd78ea13 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1795,6 +1795,7 @@  struct bpf_struct_ops_common_value {
 #define BPF_MODULE_OWNER ((void *)((0xeB9FUL << 2) + POISON_POINTER_DELTA))
 bool bpf_struct_ops_get(const void *kdata);
 void bpf_struct_ops_put(const void *kdata);
+int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff);
 int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map, void *key,
 				       void *value);
 int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_links *tlinks,
@@ -1851,6 +1852,10 @@  static inline void bpf_module_put(const void *data, struct module *owner)
 {
 	module_put(owner);
 }
+static inline int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff)
+{
+	return -ENOTSUPP;
+}
 static inline int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map,
 						     void *key,
 						     void *value)
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index bb3eabc0dc76..93ade7072976 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -1040,6 +1040,13 @@  void bpf_struct_ops_put(const void *kdata)
 	bpf_map_put(&st_map->map);
 }
 
+int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff)
+{
+	void *func_ptr = *(void **)(&st_ops->cfi_stubs[moff]);
+
+	return func_ptr ? 0 : -ENOTSUPP;
+}
+
 static bool bpf_struct_ops_valid_to_reg(struct bpf_map *map)
 {
 	struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 656766dd76df..33cb57c20d78 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -21132,6 +21132,7 @@  static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 	u32 btf_id, member_idx;
 	struct btf *btf;
 	const char *mname;
+	int err;
 
 	if (!prog->gpl_compatible) {
 		verbose(env, "struct ops programs must have a GPL compatible license\n");
@@ -21179,8 +21180,15 @@  static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 		return -EINVAL;
 	}
 
+	err = bpf_struct_ops_supported(st_ops, __btf_member_bit_offset(t, member) / 8);
+	if (err) {
+		verbose(env, "attach to unsupported member %s of struct %s\n",
+			mname, st_ops->name);
+		return err;
+	}
+
 	if (st_ops->check_member) {
-		int err = st_ops->check_member(t, member, prog);
+		err = st_ops->check_member(t, member, prog);
 
 		if (err) {
 			verbose(env, "attach to unsupported member %s of struct %s\n",
diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
index 3f88d0961e5b..554804774628 100644
--- a/net/ipv4/bpf_tcp_ca.c
+++ b/net/ipv4/bpf_tcp_ca.c
@@ -14,10 +14,6 @@ 
 /* "extern" is to avoid sparse warning.  It is only used in bpf_struct_ops.c. */
 static struct bpf_struct_ops bpf_tcp_congestion_ops;
 
-static u32 unsupported_ops[] = {
-	offsetof(struct tcp_congestion_ops, get_info),
-};
-
 static const struct btf_type *tcp_sock_type;
 static u32 tcp_sock_id, sock_id;
 static const struct btf_type *tcp_congestion_ops_type;
@@ -45,18 +41,6 @@  static int bpf_tcp_ca_init(struct btf *btf)
 	return 0;
 }
 
-static bool is_unsupported(u32 member_offset)
-{
-	unsigned int i;
-
-	for (i = 0; i < ARRAY_SIZE(unsupported_ops); i++) {
-		if (member_offset == unsupported_ops[i])
-			return true;
-	}
-
-	return false;
-}
-
 static bool bpf_tcp_ca_is_valid_access(int off, int size,
 				       enum bpf_access_type type,
 				       const struct bpf_prog *prog,
@@ -251,15 +235,6 @@  static int bpf_tcp_ca_init_member(const struct btf_type *t,
 	return 0;
 }
 
-static int bpf_tcp_ca_check_member(const struct btf_type *t,
-				   const struct btf_member *member,
-				   const struct bpf_prog *prog)
-{
-	if (is_unsupported(__btf_member_bit_offset(t, member) / 8))
-		return -ENOTSUPP;
-	return 0;
-}
-
 static int bpf_tcp_ca_reg(void *kdata, struct bpf_link *link)
 {
 	return tcp_register_congestion_control(kdata);
@@ -354,7 +329,6 @@  static struct bpf_struct_ops bpf_tcp_congestion_ops = {
 	.reg = bpf_tcp_ca_reg,
 	.unreg = bpf_tcp_ca_unreg,
 	.update = bpf_tcp_ca_update,
-	.check_member = bpf_tcp_ca_check_member,
 	.init_member = bpf_tcp_ca_init_member,
 	.init = bpf_tcp_ca_init,
 	.validate = bpf_tcp_ca_validate,