linux-kernel - eBPF verifier does not load libxdp dispatcher eBPF program

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Message-ID: <CAC=wTOhhyaoyCcAbX1xuBf5v-D=oPjjo1RLUmit=Uj9y0-3jrw@mail.gmail.com>
Date:   Mon, 23 Jan 2023 11:06:43 +0000
From:   Chris Ward <tjcw01@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Chris Ward <tjcw@...ibm.com>
Subject: eBPF verifier does not load libxdp dispatcher eBPF program

I am trying to use the 'bleeding edge' kernel to determine whether a
problem I see has already been fixed, but with this kernel the eBPF
verifier will not load the dispatcher program that is contained within
libxdp. I am testing kernel commit hash 2475bf0 which fails, and the
kernel in Ubuntu 22.04 (5.15.0-58-generic) works properly. I am
running the test case from
https://github.com/tjcw/bpf-examples/tree/tjcw-explore-sameeth ; to
build it go to the AF_XDP-filter directory and type 'make', and to run
it go to the AF_XDP-filter/runscripts/iperf3-namespace directory and
type 'sudo FILTER=af_xdp_kern PORT=50000 ./run.sh' .
The lines from the run output indicating the failure are
libbpf: prog 'xdp_dispatcher': BPF program load failed: Invalid argument
libbpf: prog 'xdp_dispatcher': -- BEGIN PROG LOAD LOG --
Func#11 is safe for any args that match its prototype
btf_vmlinux is malformed
reg type unsupported for arg#0 function xdp_dispatcher#29
0: R1=ctx(off=0,imm=0) R10=fp0
; int xdp_dispatcher(struct xdp_md *ctx)
0: (bf) r6 = r1                       ; R1=ctx(off=0,imm=0)
R6_w=ctx(off=0,imm=0)
1: (b7) r0 = 2                        ; R0_w=2
; __u8 num_progs_enabled = conf.num_progs_enabled;
2: (18) r8 = 0xffffb2f6c06d8000       ; R8_w=map_value(off=0,ks=4,vs=84,imm=0)
4: (71) r7 = *(u8 *)(r8 +0)           ; R7=1
R8=map_value(off=0,ks=4,vs=84,imm=0)
; if (num_progs_enabled < 1)
5: (15) if r7 == 0x0 goto pc+141      ; R7=1
; ret = prog0(ctx);
6: (bf) r1 = r6                       ; R1_w=ctx(off=0,imm=0)
R6=ctx(off=0,imm=0)
7: (85) call pc+140
btf_vmlinux is malformed
R1 type=ctx expected=fp
Caller passes invalid args into func#1
processed 84 insns (limit 1000000) max_states_per_insn 0 total_states
9 peak_states 9 mark_read 1
-- END PROG LOAD LOG --
libbpf: prog 'xdp_dispatcher': failed to load: -22
libbpf: failed to load object 'xdp-dispatcher.o'
libxdp: Failed to load dispatcher: Invalid argument
libxdp: Falling back to loading single prog without dispatcher

Can this regression be fixed before kernel 6.2 ships ?