On 13 May 2020, at 16:58, Eelco Chaudron wrote:
On 6 May 2020, at 3:45, Alexei Starovoitov wrote:On Wed, Apr 29, 2020 at 4:51 AM Eelco Chaudron <echaudro@xxxxxxxxxx> wrote:Hi Alexie at al. I was trying to attach a fentry/fexit trace to BPF_PROG_TYPE_EXT BPF program but I'm getting a verifier error, and not sure why. Is this supported?The intent was to make it possible. The verifier comment says:/* Cannot fentry/fexit another fentry/fexit program. * Cannot attach program extension to another extension. * It's ok to attach fentry/fexit to extension program.*/I tried it with the freplace in the fexit_bpf2bpf.c test, and here it works fine.This is the error: libbpf: -- BEGIN DUMP LOG --- libbpf: arg#0 type is not a struct Unrecognized arg#0 type PTRlooks like verifier got confused here. It should have detected correct btf_id from freplace prog. not sure what's going on.This is an EXT BPF program using the, struct xdp_md *xdp, so not sure how to connect.So I did try both: - int BPF_PROG(trace_on_entry, struct xdp_md *xdp) - int BPF_PROG(trace_on_entry, struct xdp_buff *xdp) This is the information from bpftool: ./bpftool prog show id 46 46: ext name xdp_test_I tag b5a46c6e9935298c gpl loaded_at 2020-05-13T08:54:53+0000 uid 0 xlated 136B jited 108B memlock 4096B btf_id 16 ./bpftool btf dump id 16 [1] PTR '(anon)' type_id=2 [2] STRUCT 'xdp_md' size=20 vlen=5 'data' type_id=3 bits_offset=0 'data_end' type_id=3 bits_offset=32 'data_meta' type_id=3 bits_offset=64 'ingress_ifindex' type_id=3 bits_offset=96 'rx_queue_index' type_id=3 bits_offset=128 [3] TYPEDEF '__u32' type_id=4 [4] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none) [5] FUNC_PROTO '(anon)' ret_type_id=6 vlen=1 'ctx' type_id=1 [6] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED [7] FUNC 'xdp_test_I' type_id=5 linkage=global [8] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED [9] ARRAY '(anon)' type_id=8 index_type_id=10 nr_elems=4[10] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none)[11] VAR '_license' type_id=9, linkage=global-alloc [12] DATASEC 'license' size=4 vlen=1 type_id=11 offset=0 size=4 ./bpftool prog dump xlated id 46 int xdp_test_I(struct xdp_md * ctx): ; int xdp_test_I(struct xdp_md *ctx) 0: (b7) r2 = 10 ; bpf_debug("PASS[1]: prog %u\n", ctx->ingress_ifindex); 1: (6b) *(u16 *)(r10 -8) = r2 2: (18) r2 = 0x752520676f727020 4: (7b) *(u64 *)(r10 -16) = r2 5: (18) r2 = 0x3a5d315b53534150 7: (7b) *(u64 *)(r10 -24) = r2 8: (79) r3 = *(u64 *)(r1 +40) 9: (79) r3 = *(u64 *)(r3 +0) 10: (61) r3 = *(u32 *)(r3 +256) 11: (bf) r1 = r10 ; 12: (07) r1 += -24 ; bpf_debug("PASS[1]: prog %u\n", ctx->ingress_ifindex); 13: (b7) r2 = 18 14: (85) call bpf_trace_printk#-56048 ; return XDP_PASS; 15: (b7) r0 = 2 16: (95) exit #include <linux/bpf.h> #include <bpf/bpf_helpers.h> #include <xdp/xdp_helpers.h> #define bpf_debug(fmt, ...) \ { \ char __fmt[] = fmt; \ bpf_trace_printk(__fmt, sizeof(__fmt), \ ##__VA_ARGS__); \ } SEC("xdp_test_prog_I") int xdp_test_I(struct xdp_md *ctx) { bpf_debug("PASS[1]: prog %u\n", ctx->ingress_ifindex); return XDP_PASS; }
Please ignore the second part, as I cut/pasted the wrong info. Here is the info from the actual fexit trace program, and here it’s also a pointer:
xdp-fexit]$ bpftool btf dump file xdpdump_bpf.o [1] PTR '(anon)' type_id=2[2] INT 'long long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
[3] FUNC_PROTO '(anon)' ret_type_id=4 vlen=1 'ctx' type_id=1 [4] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED [5] FUNC 'trace_on_exit' type_id=3 [6] STRUCT 'xdp_buff' size=48 vlen=6 'data' type_id=7 bits_offset=0 'data_end' type_id=7 bits_offset=64 'data_meta' type_id=7 bits_offset=128 'data_hard_start' type_id=7 bits_offset=192 'handle' type_id=8 bits_offset=256 'rxq' type_id=9 bits_offset=320 [7] PTR '(anon)' type_id=0[8] INT 'long unsigned int' size=8 bits_offset=0 nr_bits=64 encoding=(none)
[9] PTR '(anon)' type_id=10 [10] STRUCT 'xdp_rxq_info' size=16 vlen=2 'dev' type_id=11 bits_offset=0 'queue_index' type_id=12 bits_offset=64 [11] PTR '(anon)' type_id=14 [12] TYPEDEF '__u32' type_id=13 [13] INT 'unsigned int' size=4 bits_offset=0 nr_bits=32 encoding=(none) [14] STRUCT 'net_device' size=4 vlen=1 'ifindex' type_id=4 bits_offset=0 [15] INT 'char' size=1 bits_offset=0 nr_bits=8 encoding=SIGNED [16] ARRAY '(anon)' type_id=15 index_type_id=17 nr_elems=4[17] INT '__ARRAY_SIZE_TYPE__' size=4 bits_offset=0 nr_bits=32 encoding=(none)
[18] VAR '_license' type_id=16, linkage=global-alloc [19] DATASEC 'license' size=0 vlen=1 type_id=18 offset=0 size=4Maybe you can take a quick peek why it’s failing as I have no real experience with the verifier. I created some sample code that you can easily use with the following instructions:
Checkout the xdp tools repo and build it: # git clone https://github.com/chaudron/xdp-tools.git # cd xdp-tools # git checkout dev/xdpdump_multi # make # ulimit -l unlimited # cd xdp-test # cp ../lib/libxdp/xdp-dispatcher.o .# ../xdp-loader/xdp-loader load -m skb eth0 test_two_bpf.o test_bpf.o test_long_func_name.o --force
Bpftool should now show you the programs loaded, look for xdp_test_I: # bpftool prog | grep "xdp_test_I " 199: ext name xdp_test_I tag b5a46c6e9935298c gpl Now use the id (199) in the xdp-fexit test program # cd ../xdp-fexit/ # git diff - prog_fd = bpf_prog_get_fd_by_id(56); + prog_fd = bpf_prog_get_fd_by_id(199); # make Run it: # ./fexit - Found prog_fd = 3 - Opening object file - Opened object file: 0xa526b0 libbpf: load bpf program failed: Permission denied libbpf: -- BEGIN DUMP LOG --- libbpf: func#0 @0 arg#0 type is not a struct Unrecognized arg#0 type PTR 0: R1=ctx(id=0,off=0,imm=0) R10=fp0 ; int BPF_PROG(trace_on_exit, struct xdp_buff *xdp, int ret) 0: (79) r1 = *(u64 *)(r1 +0) invalid bpf_context access off=0 size=8 verification time 145 usec stack depth 0processed 1 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
libbpf: -- END LOG -- libbpf: failed to load program 'fexit/xdp_test_I' libbpf: failed to load object './xdpdump_bpf.o' ERROR: Failed to load object file: Permission denied Any ideas are welcome…
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