On 27 May 2020, at 18:54, Eelco Chaudron wrote:
On 14 May 2020, at 13:56, Eelco Chaudron wrote: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 thissupported?<SNIP>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 --forceBpftool 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 0libbpf: -- 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…Hi Alexei,I’m still trying to get attach an fentry to a EXT program, however I did found the verifier issues… If I attach fentry to an XDP entry point, the BPF_PROG() macro casts the ctx to long int *, which works:SEC("fentry/func") int BPF_PROG(trace_on_entry, struct xdp_buff *xdp) { }Is there a difference between attaching to an XDP program vs EXT that it is requiring a struct?So if I change my function to the below the verifier stops complaining for the EXT program:#define bpf_debug(fmt, ...) \ { \ char __fmt[] = fmt; \ bpf_trace_printk(__fmt, sizeof(__fmt), \ ##__VA_ARGS__); \ } SEC("fentry/func") int trace_on_entry(struct xdp_md *xdp) { bpf_debug("HALLO ID: %u", xdp->rx_queue_index); return 0; }However now the verifier complains about the following and have no clue why:libbpf: map:xdpdump_perf_map container_name:____btf_map_xdpdump_perf_map cannot be found in BTF. Missing BPF_ANNOTATE_KV_PAIR?libbpf: created map xdpdump_perf_map: fd=7 libbpf: created map xdpdump_.data: fd=8libbpf: load_attr.prog_type 26,load_attr.attach_prog_fd 6, load_attr.attach_btf_id 7libbpf: load bpf program failed: Permission denied libbpf: -- BEGIN DUMP LOG --- libbpf: Unrecognized arg#0 type PTR ; int trace_on_entry(struct xdp_md *xdp) 0: (b7) r2 = 1965367354 ; bpf_debug("HALLO ID: %u", xdp->rx_queue_index); 1: (63) *(u32 *)(r10 -8) = r2 2: (18) r2 = 0x4449204f4c4c4148 4: (7b) *(u64 *)(r10 -16) = r2 5: (b7) r2 = 0 6: (73) *(u8 *)(r10 -4) = r2 last_idx 6 first_idx 0 regs=4 stack=0 before 5: (b7) r2 = 0 7: (61) r3 = *(u32 *)(r1 +16) func 'xdp_test_I' doesn't have 3-th argument invalid bpf_context access off=16 size=4processed 7 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0libbpf: -- END LOG -- libbpf: failed to load program 'fentry/func' libbpf: failed to load object './xdpdump_multi_bpf.o'ERROR: Can't load eBPF object: Kernel verifier blocks program loading(-4007)This is the program details I try to attach too: 49: type 28 name xdp_test_I tag b5a46c6e9935298c gpl loaded_at 2020-05-27T11:40:55+0000 uid 0 xlated 136B jited 108B memlock 4096B btf_id 12 # bpftool btf dump id 12 [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
As attaching to an XDP entry point with fentry required not to use the xdp_md struct, but the xdp_buff struct, I tried this also. But as you can see below, also here it compliant about the xdp_test_I function an argument (note the xdp_test_I function is the EXT function I try to attach to).
This is the new code:
struct xdp_rxq_info {
/* Structure does not need to contain all entries,
* as "preserve_access_index" will use BTF to fix this...
*/
struct net_device *dev;
__u32 queue_index;
} __attribute__((preserve_access_index));
struct xdp_buff {
void *data;
void *data_end;
void *data_meta;
void *data_hard_start;
unsigned long handle;
struct xdp_rxq_info *rxq;
} __attribute__((preserve_access_index));
SEC("fentry/func")
int trace_on_entry(struct xdp_buff *xdp)
{
bpf_debug("HALLO ID: %u", xdp->rxq->queue_index);
return 0;
}
The result of the kernel:
libbpf: map:xdpdump_perf_map
container_name:____btf_map_xdpdump_perf_map cannot be found in BTF.
Missing BPF_ANNOTATE_KV_PAIR?
libbpf: created map xdpdump_perf_map: fd=7 libbpf: created map xdpdump_.data: fd=8 libbpf: loading kernel BTF '/sys/kernel/btf/vmlinux': 0 libbpf: prog 'fentry/func': performing 2 CO-RE offset relocslibbpf: prog 'fentry/func': relo #0: kind 0, spec is [2] xdp_buff + 0:5 => 40.0 @ &x[0].rxq
libbpf: [2] xdp_buff: found candidate [19906] xdp_bufflibbpf: prog 'fentry/func': relo #0: matching candidate #0 xdp_buff against spec [19906] xdp_buff + 0:4 => 32.0 @ &x[0].rxq: 1 libbpf: prog 'fentry/func': relo #0: patched insn #7 (LDX/ST/STX) off 40 -> 32 libbpf: prog 'fentry/func': relo #1: kind 0, spec is [9] xdp_rxq_info + 0:1 => 8.0 @ &x[0].queue_index
libbpf: [9] xdp_rxq_info: found candidate [3409] xdp_rxq_infolibbpf: prog 'fentry/func': relo #1: matching candidate #0 xdp_rxq_info against spec [3409] xdp_rxq_info + 0:1 => 8.0 @ &x[0].queue_index: 1 libbpf: prog 'fentry/func': relo #1: patched insn #8 (LDX/ST/STX) off 8 -> 8 libbpf: load_attr.prog_type 26,load_attr.attach_prog_fd 6, load_attr.attach_btf_id 7
libbpf: load bpf program failed: Permission denied
libbpf: -- BEGIN DUMP LOG ---
libbpf:
Unrecognized arg#0 type PTR
; int trace_on_entry(struct xdp_buff *xdp)
0: (b7) r2 = 1965367354
; bpf_debug("HALLO ID: %u", xdp->rxq->queue_index);
1: (63) *(u32 *)(r10 -8) = r2
2: (18) r2 = 0x4449204f4c4c4148
4: (7b) *(u64 *)(r10 -16) = r2
5: (b7) r2 = 0
6: (73) *(u8 *)(r10 -4) = r2
last_idx 6 first_idx 0
regs=4 stack=0 before 5: (b7) r2 = 0
7: (79) r1 = *(u64 *)(r1 +32)
func 'xdp_test_I' doesn't have 5-th argument
invalid bpf_context access off=32 size=8
processed 7 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 'fentry/func' libbpf: failed to load object './xdpdump_multi_bpf.o'ERROR: Can't load eBPF object: Kernel verifier blocks program loading(-4007)
Any input is welcome. I included the bpf list to see if others might have any input (thought it was already).
Cheers, Eelco
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