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pping: Add hint on XDP failure

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Due to a kernel bug for XDP programs loaded via libxdp that use global
functions (see https://lore.kernel.org/bpf/8735gkwy8h.fsf@toke.dk/t/),
XDP mode only works on relatively recent kernels where the bug is
patched (or kernels where the patch has been backported). As many
users may not have such a recent kernel they will only see a confusing
verifier error like the following:

Starting ePPing in standard mode tracking TCP on test123
libbpf: elf: skipping unrecognized data section(7) xdp_metadata
libbpf: elf: skipping unrecognized data section(7) xdp_metadata
libbpf: prog 'pping_xdp_ingress': BPF program load failed: Invalid argument
libbpf: prog 'pping_xdp_ingress': -- BEGIN PROG LOAD LOG --
Func#1 is safe for any args that match its prototype
Validating pping_xdp_ingress() func#0...
0: R1=ctx(id=0,off=0,imm=0) R10=fp0
; int pping_xdp_ingress(struct xdp_md *ctx)
0: (bf) r6 = r1                       ; R1=ctx(id=0,off=0,imm=0) R6_w=ctx(id=0,off=0,imm=0)
1: (b7) r7 = 0                        ; R7_w=invP0
; struct packet_info p_info = { 0 };
2: (7b) *(u64 *)(r10 -8) = r7         ; R7_w=invP0 R10=fp0 fp-8_w=00000000
3: (7b) *(u64 *)(r10 -16) = r7        ; R7_w=invP0 R10=fp0 fp-16_w=00000000
4: (7b) *(u64 *)(r10 -24) = r7        ; R7_w=invP0 R10=fp0 fp-24_w=00000000
5: (7b) *(u64 *)(r10 -32) = r7        ; R7_w=invP0 R10=fp0 fp-32_w=00000000
6: (7b) *(u64 *)(r10 -40) = r7        ; R7_w=invP0 R10=fp0 fp-40_w=00000000
7: (7b) *(u64 *)(r10 -48) = r7        ; R7_w=invP0 R10=fp0 fp-48_w=00000000
8: (7b) *(u64 *)(r10 -56) = r7        ; R7_w=invP0 R10=fp0 fp-56_w=00000000
9: (7b) *(u64 *)(r10 -64) = r7        ; R7_w=invP0 R10=fp0 fp-64_w=00000000
10: (7b) *(u64 *)(r10 -72) = r7       ; R7_w=invP0 R10=fp0 fp-72_w=00000000
11: (7b) *(u64 *)(r10 -80) = r7       ; R7_w=invP0 R10=fp0 fp-80_w=00000000
12: (7b) *(u64 *)(r10 -88) = r7       ; R7_w=invP0 R10=fp0 fp-88_w=00000000
13: (7b) *(u64 *)(r10 -96) = r7       ; R7_w=invP0 R10=fp0 fp-96_w=00000000
14: (7b) *(u64 *)(r10 -104) = r7      ; R7_w=invP0 R10=fp0 fp-104_w=00000000
15: (7b) *(u64 *)(r10 -112) = r7      ; R7_w=invP0 R10=fp0 fp-112_w=00000000
16: (7b) *(u64 *)(r10 -120) = r7      ; R7_w=invP0 R10=fp0 fp-120_w=00000000
17: (7b) *(u64 *)(r10 -128) = r7      ; R7_w=invP0 R10=fp0 fp-128_w=00000000
18: (bf) r2 = r10                     ; R2_w=fp0 R10=fp0
;
19: (07) r2 += -128                   ; R2=fp-128
; if (parse_packet_identifer_xdp(ctx, &p_info) < 0)
20: (85) call pc+13
R1 type=ctx expected=fp
Caller passes invalid args into func#1
processed 206542 insns (limit 1000000) max_states_per_insn 32 total_states 13238 peak_states 792 mark_read 40
-- END PROG LOAD LOG --
libbpf: failed to load program 'pping_xdp_ingress'
libbpf: failed to load object 'pping_kern.o'
Failed attaching ingress BPF program on interface test123: Invalid argument
Failed loading and attaching BPF programs in pping_kern.o

To help users that run into this issue when loading the program in
generic or unspecified mode, add a small hint suggesting to
upgrade the kernel or use the tc ingress mode instead in case
attaching the XDP program fails.

However, if loaded in native mode, instead give the suggestion to try
loading in generic mode instead. While libbpf and libxdp already add
some messages hinting at this, this hint clarifies how to do this with
ePPing (using the --xdp-mode argument).

Signed-off-by: Simon Sundberg <simon.sundberg@kau.se>
This commit is contained in:
Simon Sundberg
2022-11-03 16:58:12 +01:00
parent ff0c5a9b4a
commit 0b0b1e9552
1 changed files with 10 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
pping/pping.c
View File

@@ -911,6 +911,16 @@ static int load_attach_bpfprogs(struct bpf_object **obj,
/* xdp_attach() loads 'obj' through libxdp */
err = xdp_attach(*obj, config->ingress_prog, config->ifindex,
&config->xdp_prog, config->xdp_mode);
if (err) {
fprintf(stderr, "Failed attaching XDP program\n");
if (config->xdp_mode == XDP_MODE_NATIVE)
fprintf(stderr,
"%s may not have driver support for XDP, try --xdp-mode generic instead\n",
config->ifname);
else
fprintf(stderr,
"Try updating kernel or use --ingress-hook tc instead\n");
}
} else {
err = bpf_object__load(*obj);
if (err) {