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This was > observed during development of a MIPS32 JIT but is verifier-related. > > Initial troubleshooting [2] points to an unchecked NULL dereference in > btf_type_by_id(), with an unexpected BTF type ID. The root cause is > unclear, whether source of the ID or a potential underlying BTF > problem. Do you know what is the faulty btf ID number? What is the maximum id for vmlinux BTF? The involved helper is bpf_sk_release. static const struct bpf_func_proto bpf_sk_release_proto = { .func = bpf_sk_release, .gpl_only = false, .ret_type = RET_INTEGER, .arg1_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON, }; Eventually, the btf_id is taken from btf_sock_ids[6] where btf_sock_ids is a kernel global variable. Could you check btf_sock_ids[6] to see whether the number makes sense? The id is computed by resolve_btfids in tools/bpf/resolve_btfids, you might add verbose mode to your linux build to get more information. > > Has this been seen before? How best to debug this further or resolve? > What other details would be useful for BPF kernel developers? > > Thanks for any help, > Tony > > [1]: > (Host details) > kodidev:~/openwrt-project$ ./staging_dir/host/bin/pahole --version > v1.21 > > (Target details) > root@OpenWrt:/# uname -a > Linux OpenWrt 5.10.41 #0 SMP Tue Jun 1 00:54:31 2021 mips GNU/Linux > > root@OpenWrt:~# sysctl net.core.bpf_jit_enable=0; ./test_verifier 826 828 > net.core.bpf_jit_enable = 0 > > #826/p reference tracking: branch tracking valid pointer null comparison OK > #827/p reference tracking: branch tracking valid pointer value comparison OK > CPU 0 Unable to handle kernel paging request at virtual address > 00000000, epc == 80244654, ra == 80244654 > Oops[#1]: > CPU: 0 PID: 16274 Comm: test_verifier Not tainted 5.10.41 #0 > $ 0 : 00000000 00000001 00000000 0000a8a2 > $ 4 : 835ac580 a6280000 00000000 00000001 > $ 8 : 835ac580 a6280000 00000000 02020202 > $12 : 8348de58 834ba800 00000000 00000000 > $16 : 835ac580 8098be2c fffffff3 834bdb38 > $20 : 8098be0c 00000001 00000018 00000000 > $24 : 00000000 01415415 > $28 : 834bc000 834bdac8 00000005 80244654 > Hi : 00000017 > Lo : 0a3d70a2 > epc : 80244654 kernel_type_name+0x20/0x38 > ra : 80244654 kernel_type_name+0x20/0x38 > Status: 1000a403 KERNEL EXL IE > Cause : 00800008 (ExcCode 02) > BadVA : 00000000 > PrId : 00019300 (MIPS 24Kc) > Modules linked in: pppoe ppp_async pppox ppp_generic mac80211_hwsim > mac80211 iptable_nat ipt_REJECT cfg80211 xt_time xt_tcpudp xt_tcpmss > xt_statistic xt_state xt_recent xt_nat xt_multiport xt_mark xt_mac > xt_limit xt_length xt_hl xt_helper xt_ecn xt_dscp xt_conntrack > xt_connmark xt_connlimit xt_connbytes xt_comment xt_TCPMSS xt_REDIRECT > xt_MASQUERADE xt_LOG xt_HL xt_FLOWOFFLOAD xt_DSCP xt_CT xt_CLASSIFY > slhc sch_mqprio sch_cake pcnet32 nf_reject_ipv4 nf_nat nf_log_ipv4 > nf_flow_table nf_conntrack_netlink nf_conncount iptable_raw > iptable_mangle iptable_filter ipt_ECN ip_tables crc_ccitt compat > cls_flower act_vlan pktgen sch_teql sch_sfq sch_red sch_prio sch_pie > sch_multiq sch_gred sch_fq sch_dsmark sch_codel em_text em_nbyte > em_meta em_cmp act_simple act_police act_pedit act_ipt act_csum > libcrc32c em_ipset cls_bpf act_bpf act_ctinfo act_connmark > nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 sch_tbf sch_ingress sch_htb > sch_hfsc em_u32 cls_u32 cls_tcindex cls_route cls_matchall cls_fw > cls_flow cls_basic act_skbedit act_mirred act_gact xt_set > ip_set_list_set ip_set_hash_netportnet ip_set_hash_netport > ip_set_hash_netnet ip_set_hash_netiface ip_set_hash_net > ip_set_hash_mac ip_set_hash_ipportnet ip_set_hash_ipportip > ip_set_hash_ipport ip_set_hash_ipmark ip_set_hash_ip > ip_set_bitmap_port ip_set_bitmap_ipmac ip_set_bitmap_ip ip_set > nfnetlink nf_log_ipv6 nf_log_common ip6table_mangle ip6table_filter > ip6_tables ip6t_REJECT x_tables nf_reject_ipv6 ifb dummy netlink_diag > mii > Process test_verifier (pid: 16274, threadinfo=c1418596, task=05765195, > tls=77e5aec8) > Stack : 83428000 83428000 8098be2c 00000000 83428000 8024af78 834bacdc 834bb000 > a98a0000 834e2580 834e2c00 00000000 834e2c00 8023da9c 834bb070 00000013 > 80925164 80924f44 00000000 80925164 00000000 83428140 80bc3864 834bb070 > 834e2c00 00000000 00000010 802c441c 00000000 00000000 00000000 00000000 > 00000000 00000000 00000000 00000000 00000000 00000056 00000000 00000000 > ... > Call Trace: > [<80244654>] kernel_type_name+0x20/0x38 > [<8024af78>] check_helper_call+0x1c9c/0x1dbc > [<8024d008>] do_check_common+0x1f70/0x2a3c > [<8024fb6c>] bpf_check+0x18f8/0x2308 > [<802369ec>] bpf_prog_load+0x378/0x860 > [<80237e1c>] __do_sys_bpf+0x3e0/0x2100 > [<801142d8>] syscall_common+0x34/0x58 > > Code: afbf0014 0c099b58 02002025 <8c450000> 8fbf0014 02002025 > 8fb00010 08099b4f 27bd0018 > > ---[ end trace ab13ac5f89eb825b ]--- > Kernel panic - not syncing: Fatal exception > Rebooting in 3 seconds.. > QEMU: Terminated > > > [2]: > Function Code: > ============== > const char *kernel_type_name(u32 id) > { > return btf_name_by_offset(btf_vmlinux, > btf_type_by_id(btf_vmlinux, id)->name_off); > } > > const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id) > { > if (type_id > btf->nr_types) > return NULL; > > return btf->types[type_id]; > } > > Disassembled Code: > ================== > 0x0000000000000000: AF BF 00 14 sw $ra, 0x14($sp) > 0x0000000000000004: 0C 09 9B 58 jal btf_type_by_id > 0x0000000000000008: 02 00 20 25 move $a0, $s0 > 0x000000000000000c: 8C 45 00 00 lw $a1, ($v0) <-- NPE > 0x0000000000000010: 8F BF 00 14 lw $ra, 0x14($sp) > 0x0000000000000014: 02 00 20 25 move $a0, $s0 > 0x0000000000000018: 8F B0 00 10 lw $s0, 0x10($sp) > 0x000000000000001c: 08 09 9B 4F j btf_name_by_offset > 0x0000000000000020: 27 BD 00 18 addiu $sp, $sp, 0x18 >