Merge branch 'bpf: Support multi-attach for freplace'

Toke Høiland-Jørgensen says:

====================
This series adds support attaching freplace BPF programs to multiple targets.
This is needed to support incremental attachment of multiple XDP programs using
the libxdp dispatcher model.

Patch 1 moves prog_aux->linked_prog and the trampoline to be embedded in
bpf_tracing_link on attach, and freed by the link release logic, and introduces
a mutex to protect the writing of the pointers in prog->aux.

Based on this refactoring (and previously applied patches), it becomes pretty
straight-forward to support multiple-attach for freplace programs (patch 2).
This is simply a matter of creating a second bpf_tracing_link if a target is
supplied. However, for API consistency with other types of link attach, this
option is added to the BPF_LINK_CREATE API instead of extending
bpf_raw_tracepoint_open().

Patch 3 is a port of Jiri Olsa's patch to support fentry/fexit on freplace
programs. His approach of getting the target type from the target program
reference no longer works after we've gotten rid of linked_prog (because the
bpf_tracing_link reference disappears on attach). Instead, we used the saved
reference to the target prog type that is also used to verify compatibility on
secondary freplace attachment.

Patch 4 is the accompanying libbpf update, and patches 5-7 are selftests: patch
5 tests for the multi-freplace functionality itself; patch 6 is Jiri's previous
selftest for the fentry-to-freplace fix; patch 7 is a test for the change
introduced in the previously-applied patches, blocking MODIFY_RETURN functions
from attaching to other BPF programs.

With this series, libxdp and xdp-tools can successfully attach multiple programs
one at a time. To play with this, use the 'freplace-multi-attach' branch of
xdp-tools:

$ git clone --recurse-submodules --branch freplace-multi-attach https://github.com/xdp-project/xdp-tools
$ cd xdp-tools/xdp-loader
$ make
$ sudo ./xdp-loader load veth0 ../lib/testing/xdp_drop.o
$ sudo ./xdp-loader load veth0 ../lib/testing/xdp_pass.o
$ sudo ./xdp-loader status

The series is also available here:
https://git.kernel.org/pub/scm/linux/kernel/git/toke/linux.git/log/?h=bpf-freplace-multi-attach-alt-10

Changelog:

v10:
  - Dial back the s/tgt_/dst_/ replacement a bit
  - Fix smatch warning (from ktest robot)
  - Rebase to bpf-next, drop already-applied patches

v9:
  - Clarify commit message of patch 3
  - Add new struct bpf_attach_target_info for returning from
    bpf_check_attach_target() and passing to bpf_trampoline_get()
  - Move trampoline key computation into a helper
  - Make sure we don't break bpffs debug umh
  - Add some comment blocks explaining the logic flow in
    bpf_tracing_prog_attach()
  - s/tgt_/dst_/ in prog->aux, and for local variables using those members
  - Always drop dst_trampoline and dst_prog from prog->aux on first attach
  - Don't remove syscall fmod_ret test from selftest benchmarks
  - Add saved_ prefix to dst_{prog,attach}_type members in prog_aux
  - Drop prog argument from check_attach_modify_return()
  - Add comment about possible NULL of tr_link->tgt_prog on link_release()

v8:
  - Add a separate error message when trying to attach FMOD_REPLACE to tgt_prog
  - Better error messages in bpf_program__attach_freplace()
  - Don't lock mutex when setting tgt_* pointers in prog create and verifier
  - Remove fmod_ret programs from benchmarks in selftests (new patch 11)
  - Fix a few other nits in selftests

v7:
  - Add back missing ptype == prog->type check in link_create()
  - Use tracing_bpf_link_attach() instead of separate freplace_bpf_link_attach()
  - Don't break attachment of bpf_iters in libbpf (by clobbering link_create.iter_info)

v6:
  - Rebase to latest bpf-next
  - Simplify logic in bpf_tracing_prog_attach()
  - Don't create a new attach_type for link_create(), disambiguate on prog->type
    instead
  - Use raw_tracepoint_open() in libbpf bpf_program__attach_ftrace() if called
    with NULL target
  - Switch bpf_program__attach_ftrace() to take function name as parameter
    instead of btf_id
  - Add a patch disallowing MODIFY_RETURN programs from attaching to other BPF
    programs, and an accompanying selftest (patches 1 and 10)

v5:
  - Fix typo in inline function definition of bpf_trampoline_get()
  - Don't put bpf_tracing_link in prog->aux, use a mutex to protect tgt_prog and
    trampoline instead, and move them to the link on attach.
  - Restore Jiri as author of the last selftest patch

v4:
  - Cleanup the refactored check_attach_btf_id() to make the logic easier to follow
  - Fix cleanup paths for bpf_tracing_link
  - Use xchg() for removing the bpf_tracing_link from prog->aux and restore on (some) failures
  - Use BPF_LINK_CREATE operation to create link with target instead of extending raw_tracepoint_open
  - Fold update of tools/ UAPI header into main patch
  - Update arg dereference patch to use skeletons and set_attach_target()

v3:
  - Get rid of prog_aux->linked_prog entirely in favour of a bpf_tracing_link
  - Incorporate Jiri's fix for attaching fentry to freplace programs

v2:
  - Drop the log arguments from bpf_raw_tracepoint_open
  - Fix kbot errors
  - Rebase to latest bpf-next
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 18 insertions, 8 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 768b533ba48e..50e5c4b52bd1 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -640,8 +640,8 @@ static __always_inline unsigned int bpf_dispatcher_nop_func(
 	return bpf_func(ctx, insnsi);
 }
 #ifdef CONFIG_BPF_JIT
-int bpf_trampoline_link_prog(struct bpf_prog *prog);
-int bpf_trampoline_unlink_prog(struct bpf_prog *prog);
+int bpf_trampoline_link_prog(struct bpf_prog *prog, struct bpf_trampoline *tr);
+int bpf_trampoline_unlink_prog(struct bpf_prog *prog, struct bpf_trampoline *tr);
 struct bpf_trampoline *bpf_trampoline_get(u64 key,
 					  struct bpf_attach_target_info *tgt_info);
 void bpf_trampoline_put(struct bpf_trampoline *tr);
@@ -688,11 +688,13 @@ void bpf_image_ksym_del(struct bpf_ksym *ksym);
 void bpf_ksym_add(struct bpf_ksym *ksym);
 void bpf_ksym_del(struct bpf_ksym *ksym);
 #else
-static inline int bpf_trampoline_link_prog(struct bpf_prog *prog)
+static inline int bpf_trampoline_link_prog(struct bpf_prog *prog,
+					   struct bpf_trampoline *tr)
 {
 	return -ENOTSUPP;
 }
-static inline int bpf_trampoline_unlink_prog(struct bpf_prog *prog)
+static inline int bpf_trampoline_unlink_prog(struct bpf_prog *prog,
+					     struct bpf_trampoline *tr)
 {
 	return -ENOTSUPP;
 }
@@ -763,7 +765,11 @@ struct bpf_prog_aux {
 	u32 max_rdonly_access;
 	u32 max_rdwr_access;
 	const struct bpf_ctx_arg_aux *ctx_arg_info;
-	struct bpf_prog *linked_prog;
+	struct mutex dst_mutex; /* protects dst_* pointers below, *after* prog becomes visible */
+	struct bpf_prog *dst_prog;
+	struct bpf_trampoline *dst_trampoline;
+	enum bpf_prog_type saved_dst_prog_type;
+	enum bpf_attach_type saved_dst_attach_type;
 	bool verifier_zext; /* Zero extensions has been inserted by verifier. */
 	bool offload_requested;
 	bool attach_btf_trace; /* true if attaching to BTF-enabled raw tp */
@@ -771,7 +777,6 @@ struct bpf_prog_aux {
 	bool sleepable;
 	bool tail_call_reachable;
 	enum bpf_tramp_prog_type trampoline_prog_type;
-	struct bpf_trampoline *trampoline;
 	struct hlist_node tramp_hlist;
 	/* BTF_KIND_FUNC_PROTO for valid attach_btf_id */
 	const struct btf_type *attach_func_proto;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 96ddb00b91dc..2b1d3f16cbd1 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -639,8 +639,13 @@ union bpf_attr {
 		};
 		__u32		attach_type;	/* attach type */
 		__u32		flags;		/* extra flags */
-		__aligned_u64	iter_info;	/* extra bpf_iter_link_info */
-		__u32		iter_info_len;	/* iter_info length */
+		union {
+			__u32		target_btf_id;	/* btf_id of target to attach to */
+			struct {
+				__aligned_u64	iter_info;	/* extra bpf_iter_link_info */
+				__u32		iter_info_len;	/* iter_info length */
+			};
+		};
 	} link_create;
 
 	struct { /* struct used by BPF_LINK_UPDATE command */