Re: eBPF verifier does not load libxdp dispatcher eBPF program

[Eduard Zingerman <eddyz87@gmail.com>]

On Tue, 2025-02-25 at 16:55 +0100, Marc Kleine-Budde wrote:
> On 23.01.2023 12:35:41, Chris Ward wrote:
> > The 5.15.0 kernel (built by 'git checkout v5.15' from the kernel.org
> > torvalds tree) fails in the same way that the 6.2.0-rc5+ kernel fails.
> > So it seems that something Canonical did for the Ubuntu 20.04 kernel
> > causes eBPF to work correctly.
> > 
> > On Mon, 23 Jan 2023 at 11:06, Chris Ward <tjcw01@gmail.com> wrote:
> > > 
> > > 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 ?
> 
> I'm seeing the same failure on 32 bit ARM on v6.13.
> 
> Have you found a solution?
> 
> regards,
> Marc
> 

Hello,

When I try the link from the discussion:
https://github.com/tjcw/bpf-examples/tree/tjcw-explore-sameeth
I get a 404 error from github.

(Sorry for previous email, it was sent unintentionally).