bpf: remove useless version check for prog load

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

Daniel Borkmann committed 7 years ago

Commit 6c4fc201 parent 034565d3 files · +18 −7Browse files

Showing the changes to include/uapi/linux (1 of 3 files). Show all

Unified · Split

include/uapi/linux/bpf.h+9−1

@@ -133,6 +133,14 @@ enum bpf_map_type { · 132 unmodified lines
133	133	BPF_MAP_TYPE_STACK,
134	134	};
135	135
	136	+/* Note that tracing related programs such as
	137	+ * BPF_PROG_TYPE_{KPROBE,TRACEPOINT,PERF_EVENT,RAW_TRACEPOINT}
	138	+ * are not subject to a stable API since kernel internal data
	139	+ * structures can change from release to release and may
	140	+ * therefore break existing tracing BPF programs. Tracing BPF
	141	+ * programs correspond to /a/ specific kernel which is to be
	142	+ * analyzed, and not /a/ specific kernel /and/ all future ones.
	143	+ */
136	144	enum bpf_prog_type {
137	145	BPF_PROG_TYPE_UNSPEC,
138	146	BPF_PROG_TYPE_SOCKET_FILTER,
@@ -343,7 +351,7 @@ union bpf_attr { · 204 unmodified lines
343	351	__u32 log_level; /* verbosity level of verifier */
344	352	__u32 log_size; /* size of user buffer */
345	353	__aligned_u64 log_buf; /* user supplied buffer */
346		− __u32 kern_version; /* checked when prog_type=kprobe */
	354	+ __u32 kern_version; /* not used */
347	355	__u32 prog_flags;
348	356	char prog_name[BPF_OBJ_NAME_LEN];
349	357	__u32 prog_ifindex; /* ifindex of netdev to prep for */