Merge branch 'bpf-cgroup-multi-prog'

Alexei Starovoitov says:

====================
bpf: muli prog support for cgroup-bpf

v1->v2:
- fixed accidentally swapped two lines which caused static_key not going to zero
- addressed Martin's feedback and changed prog_query to be consistent
  with verifier output: return -enospc and fill supplied buffer instead
  of just returning -enospc when buffer is too small to fit all prog_ids

v1:
cgroup-bpf use cases are getting more advanced and running only
one program per cgroup is no longer enough. Therefore introduce
support for attaching multiple programs per cgroup and running
a set of effective programs.

These patches introduces BPF_F_ALLOW_MULTI flag for BPF_PROG_ATTACH cmd.
The default is still NONE and behavior of BPF_F_ALLOW_OVERRIDE flag
is unchanged.
The difference between three possible flags for BPF_PROG_ATTACH command:
- NONE(default): No further bpf programs allowed in the subtree.
- BPF_F_ALLOW_OVERRIDE: If a sub-cgroup installs some bpf program,
  the program in this cgroup yields to sub-cgroup program.
- BPF_F_ALLOW_MULTI: If a sub-cgroup installs some bpf program,
  that cgroup program gets run in addition to the program in this cgroup.

Most of the logic is in patch 1. Even when cgroup doesn't have
any programs attached its set of effective program can be non-empty.
To quickly execute them and avoid penalizing cgroups without
any effective programs introduce 'struct bpf_prog_array'
which has an optimization for cgroups with zero effective programs.

Patch 2 introduces BPF_PROG_QUERY command for introspection
Patch 3 makes verifier more strict for cgroup-bpf program types.
Patch 4+ are tests.

More details in individual patches
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 52 insertions, 3 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 6d2137b4cf38..cb2b9f95160a 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -92,6 +92,7 @@ enum bpf_cmd {
 	BPF_PROG_GET_FD_BY_ID,
 	BPF_MAP_GET_FD_BY_ID,
 	BPF_OBJ_GET_INFO_BY_FD,
+	BPF_PROG_QUERY,
 };
 
 enum bpf_map_type {
@@ -143,11 +144,47 @@ enum bpf_attach_type {
 
 #define MAX_BPF_ATTACH_TYPE __MAX_BPF_ATTACH_TYPE
 
-/* If BPF_F_ALLOW_OVERRIDE flag is used in BPF_PROG_ATTACH command
- * to the given target_fd cgroup the descendent cgroup will be able to
- * override effective bpf program that was inherited from this cgroup
+/* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
+ *
+ * NONE(default): No further bpf programs allowed in the subtree.
+ *
+ * BPF_F_ALLOW_OVERRIDE: If a sub-cgroup installs some bpf program,
+ * the program in this cgroup yields to sub-cgroup program.
+ *
+ * BPF_F_ALLOW_MULTI: If a sub-cgroup installs some bpf program,
+ * that cgroup program gets run in addition to the program in this cgroup.
+ *
+ * Only one program is allowed to be attached to a cgroup with
+ * NONE or BPF_F_ALLOW_OVERRIDE flag.
+ * Attaching another program on top of NONE or BPF_F_ALLOW_OVERRIDE will
+ * release old program and attach the new one. Attach flags has to match.
+ *
+ * Multiple programs are allowed to be attached to a cgroup with
+ * BPF_F_ALLOW_MULTI flag. They are executed in FIFO order
+ * (those that were attached first, run first)
+ * The programs of sub-cgroup are executed first, then programs of
+ * this cgroup and then programs of parent cgroup.
+ * When children program makes decision (like picking TCP CA or sock bind)
+ * parent program has a chance to override it.
+ *
+ * A cgroup with MULTI or OVERRIDE flag allows any attach flags in sub-cgroups.
+ * A cgroup with NONE doesn't allow any programs in sub-cgroups.
+ * Ex1:
+ * cgrp1 (MULTI progs A, B) ->
+ *    cgrp2 (OVERRIDE prog C) ->
+ *      cgrp3 (MULTI prog D) ->
+ *        cgrp4 (OVERRIDE prog E) ->
+ *          cgrp5 (NONE prog F)
+ * the event in cgrp5 triggers execution of F,D,A,B in that order.
+ * if prog F is detached, the execution is E,D,A,B
+ * if prog F and D are detached, the execution is E,A,B
+ * if prog F, E and D are detached, the execution is C,A,B
+ *
+ * All eligible programs are executed regardless of return code from
+ * earlier programs.
  */
 #define BPF_F_ALLOW_OVERRIDE	(1U << 0)
+#define BPF_F_ALLOW_MULTI	(1U << 1)
 
 /* If BPF_F_STRICT_ALIGNMENT is used in BPF_PROG_LOAD command, the
  * verifier will perform strict alignment checking as if the kernel
@@ -175,6 +212,9 @@ enum bpf_attach_type {
 /* Specify numa node during map creation */
 #define BPF_F_NUMA_NODE		(1U << 2)
 
+/* flags for BPF_PROG_QUERY */
+#define BPF_F_QUERY_EFFECTIVE	(1U << 0)
+
 #define BPF_OBJ_NAME_LEN 16U
 
 union bpf_attr {
@@ -253,6 +293,15 @@ union bpf_attr {
 		__u32		info_len;
 		__aligned_u64	info;
 	} info;
+
+	struct { /* anonymous struct used by BPF_PROG_QUERY command */
+		__u32		target_fd;	/* container object to query */
+		__u32		attach_type;
+		__u32		query_flags;
+		__u32		attach_flags;
+		__aligned_u64	prog_ids;
+		__u32		prog_cnt;
+	} query;
 } __attribute__((aligned(8)));
 
 /* BPF helper function descriptions: