bpf: remove useless version check for prog load

borkmann · Alexei Starovoitov · commit 6c4fc209fcf9 · 2018-12-17T13:41:35.000-08:00
Existing libraries and tracing frameworks work around this kernel version check by automatically deriving the kernel version from uname(3) or similar such that the user does not need to do it manually; these workarounds also make the version check useless at the same time. Moreover, most other BPF tracing types enabling bpf_probe_read()-like functionality have /not/ adapted this check, and in general these days it is well understood anyway that all the tracing programs are not stable with regards to future kernels as kernel internal data structures are subject to change from release to release. Back at last netconf we discussed [0] and agreed to remove this check from bpf_prog_load() and instead document it here in the uapi header that there is no such guarantee for stable API for these programs. [0] http://vger.kernel.org/netconf2018_files/DanielBorkmann_netconf2018.pdf Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Quentin Monnet <quentin.monnet@netronome.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
@@ -133,6 +133,14 @@ enum bpf_map_type {
 	BPF_MAP_TYPE_STACK,
 };
 
+/* Note that tracing related programs such as
+ * BPF_PROG_TYPE_{KPROBE,TRACEPOINT,PERF_EVENT,RAW_TRACEPOINT}
+ * are not subject to a stable API since kernel internal data
+ * structures can change from release to release and may
+ * therefore break existing tracing BPF programs. Tracing BPF
+ * programs correspond to /a/ specific kernel which is to be
+ * analyzed, and not /a/ specific kernel /and/ all future ones.
+ */
 enum bpf_prog_type {
 	BPF_PROG_TYPE_UNSPEC,
 	BPF_PROG_TYPE_SOCKET_FILTER,
@@ -343,7 +351,7 @@ union bpf_attr {
 		__u32		log_level;	/* verbosity level of verifier */
 		__u32		log_size;	/* size of user buffer */
 		__aligned_u64	log_buf;	/* user supplied buffer */
-		__u32		kern_version;	/* checked when prog_type=kprobe */
+		__u32		kern_version;	/* not used */
 		__u32		prog_flags;
 		char		prog_name[BPF_OBJ_NAME_LEN];
 		__u32		prog_ifindex;	/* ifindex of netdev to prep for */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
@@ -1473,11 +1473,6 @@ static int bpf_prog_load(union bpf_attr *attr, union bpf_attr __user *uattr)
 
 	if (attr->insn_cnt == 0 || attr->insn_cnt > BPF_MAXINSNS)
 		return -E2BIG;
-
-	if (type == BPF_PROG_TYPE_KPROBE &&
-	    attr->kern_version != LINUX_VERSION_CODE)
-		return -EINVAL;
-
 	if (type != BPF_PROG_TYPE_SOCKET_FILTER &&
 	    type != BPF_PROG_TYPE_CGROUP_SKB &&
 	    !capable(CAP_SYS_ADMIN))
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
@@ -133,6 +133,14 @@ enum bpf_map_type {
 	BPF_MAP_TYPE_STACK,
 };
 
+/* Note that tracing related programs such as
+ * BPF_PROG_TYPE_{KPROBE,TRACEPOINT,PERF_EVENT,RAW_TRACEPOINT}
+ * are not subject to a stable API since kernel internal data
+ * structures can change from release to release and may
+ * therefore break existing tracing BPF programs. Tracing BPF
+ * programs correspond to /a/ specific kernel which is to be
+ * analyzed, and not /a/ specific kernel /and/ all future ones.
+ */
 enum bpf_prog_type {
 	BPF_PROG_TYPE_UNSPEC,
 	BPF_PROG_TYPE_SOCKET_FILTER,
@@ -343,7 +351,7 @@ union bpf_attr {
 		__u32		log_level;	/* verbosity level of verifier */
 		__u32		log_size;	/* size of user buffer */
 		__aligned_u64	log_buf;	/* user supplied buffer */
-		__u32		kern_version;	/* checked when prog_type=kprobe */
+		__u32		kern_version;	/* not used */
 		__u32		prog_flags;
 		char		prog_name[BPF_OBJ_NAME_LEN];
 		__u32		prog_ifindex;	/* ifindex of netdev to prep for */
