[PATCH bpf-next 1/2] libbpf: Add probe for large INSN limit

[Michal Rostecki]

Introduce a new probe which checks whether kernel has large maximum
program size (1M) which was increased in commit c04c0d2b968a ("bpf:
increase complexity limit and maximum program size").

Based on the similar check in Cilium[0], authored by Daniel Borkmann.

[0] https://github.com/cilium/cilium/commit/657d0f585afd26232cfa5d4e70b6f64d2ea91596

Co-authored-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Michal Rostecki <mrostecki@xxxxxxx>
---
 tools/lib/bpf/libbpf.h        |  1 +
 tools/lib/bpf/libbpf.map      |  1 +
 tools/lib/bpf/libbpf_probes.c | 23 +++++++++++++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index fe592ef48f1b..26bf539f1b3c 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -521,6 +521,7 @@ LIBBPF_API bool bpf_probe_prog_type(enum bpf_prog_type prog_type,
 LIBBPF_API bool bpf_probe_map_type(enum bpf_map_type map_type, __u32 ifindex);
 LIBBPF_API bool bpf_probe_helper(enum bpf_func_id id,
 				 enum bpf_prog_type prog_type, __u32 ifindex);
+LIBBPF_API bool bpf_probe_large_insn_limit(__u32 ifindex);
 
 /*
  * Get bpf_prog_info in continuous memory
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index e9713a574243..b300d74c921a 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -219,6 +219,7 @@ LIBBPF_0.0.7 {
 		bpf_object__detach_skeleton;
 		bpf_object__load_skeleton;
 		bpf_object__open_skeleton;
+		bpf_probe_large_insn_limit;
 		bpf_prog_attach_xattr;
 		bpf_program__attach;
 		bpf_program__name;
diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
index a9eb8b322671..925f95106a52 100644
--- a/tools/lib/bpf/libbpf_probes.c
+++ b/tools/lib/bpf/libbpf_probes.c
@@ -17,6 +17,8 @@
 #include "libbpf.h"
 #include "libbpf_internal.h"
 
+#define INSN_REPEAT 4128
+
 static bool grep(const char *buffer, const char *pattern)
 {
 	return !!strstr(buffer, pattern);
@@ -321,3 +323,24 @@ bool bpf_probe_helper(enum bpf_func_id id, enum bpf_prog_type prog_type,
 
 	return res;
 }
+
+/*
+ * Probe for availability of kernel commit (5.3):
+ *
+ * c04c0d2b968a ("bpf: increase complexity limit and maximum program size")
+ */
+bool bpf_probe_large_insn_limit(__u32 ifindex)
+{
+	struct bpf_insn insns[INSN_REPEAT + 1];
+	int i;
+
+	for (i = 0; i < INSN_REPEAT; i++)
+		insns[i] = BPF_MOV64_IMM(BPF_REG_0, 1);
+	insns[INSN_REPEAT] = BPF_EXIT_INSN();
+
+	errno = 0;
+	probe_load(BPF_PROG_TYPE_SCHED_CLS, insns, ARRAY_SIZE(insns), NULL, 0,
+		   ifindex);
+
+	return errno != E2BIG && errno != EINVAL;
+}
-- 
2.16.4