bpf: Allow BPF_PROG_TYPE_STRUCT_OPS programs to be sleepable

BPF struct_ops programs currently cannot be marked as sleepable. This
need not be the case -- struct_ops programs can be sleepable, and e.g.
invoke kfuncs that export the KF_SLEEPABLE flag. So as to allow future
struct_ops programs to invoke such kfuncs, this patch updates the
verifier to allow struct_ops programs to be sleepable. A follow-on patch
will add support to libbpf for specifying struct_ops.s as a sleepable
struct_ops program, and then another patch will add testcases to the
dummy_st_ops selftest suite which test sleepable struct_ops behavior.
Signed-off-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230125164735.785732-2-void@manifault.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/verifier.c

@@ -17114,7 +17114,8 @@ static bool can_be_sleepable(struct bpf_prog *prog)
 		}
 	}
 	return prog->type == BPF_PROG_TYPE_LSM ||
-	       prog->type == BPF_PROG_TYPE_KPROBE; /* only for uprobes */
+	       prog->type == BPF_PROG_TYPE_KPROBE /* only for uprobes */ ||
+	       prog->type == BPF_PROG_TYPE_STRUCT_OPS;
 }
 
 static int check_attach_btf_id(struct bpf_verifier_env *env)
@@ -17136,7 +17137,7 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 	}
 
 	if (prog->aux->sleepable && !can_be_sleepable(prog)) {
-		verbose(env, "Only fentry/fexit/fmod_ret, lsm, iter and uprobe programs can be sleepable\n");
+		verbose(env, "Only fentry/fexit/fmod_ret, lsm, iter, uprobe, and struct_ops programs can be sleepable\n");
 		return -EINVAL;
 	}
 

tools/testing/selftests/bpf/verifier/sleepable.c

@@ -85,7 +85,7 @@
 	.expected_attach_type = BPF_TRACE_RAW_TP,
 	.kfunc = "sched_switch",
 	.result = REJECT,
-	.errstr = "Only fentry/fexit/fmod_ret, lsm, iter and uprobe programs can be sleepable",
+	.errstr = "Only fentry/fexit/fmod_ret, lsm, iter, uprobe, and struct_ops programs can be sleepable",
 	.flags = BPF_F_SLEEPABLE,
 	.runs = -1,
 },