On Wed, Dec 4, 2019 at 5:20 AM Eelco Chaudron <echaudro@xxxxxxxxxx> wrote:
>
>
>
> On 2 Dec 2019, at 17:48, Yonghong Song wrote:
>
> > On 12/2/19 8:34 AM, Eelco Chaudron wrote:
> >> On 29 Nov 2019, at 17:52, Yonghong Song wrote:
>
> <SNIP>
> >
> > You need to build the kernel with
> > CONFIG_DEBUG_INFO_BTF=y
> > Make sure on the build machine you have recent pahole version >= 1.13.
>
> With the latest LLVM and CONFIG_DEBUG_INFO_BTF=y the self-test for
> bpf2bpf is passing!
>
>
> However I still have problems with my code, which is getting to the next
> step, but no my program is killed when trying to load the eBPG fexit
> code. If I replace my generated eBPF programs for the once generated by
> the self-test (test_pkt_access.o/fexit_bpf2bpf.o) it works fine.
>
>
> I decided to build my objects just like the example programs (so have a
> hacked build.sh file) but I get the same results. I.e. being killed by
> the kernel:
>
> bpf(BPF_BTF_LOAD,
> {btf="\237\353\1\0\30\0\0\0\0\0\0\0\330\0\0\0\330\0\0\0\244\0\0\0\0\0\0\0\0\0\0\2"...,
> btf_log_buf=NULL, btf_size=404, btf_log_size=0, btf_log_level=0}, 120) =
> 6
> bpf(BPF_OBJ_GET_INFO_BY_FD, {info={bpf_fd=3, info_len=208,
> info=0x7ffdfbdac3b0}}, 120) = 0
> bpf(BPF_OBJ_GET_INFO_BY_FD, {info={bpf_fd=3, info_len=208,
> info=0xafb600}}, 120) = 0
> bpf(BPF_BTF_GET_FD_BY_ID, {btf_id=90}, 120) = 5
> bpf(BPF_OBJ_GET_INFO_BY_FD, {info={bpf_fd=5, info_len=16,
> info=0x7ffdfbdac4b0}}, 120) = 0
> - Opened object file: 0xafb440
> bpf(BPF_PROG_LOAD, {prog_type=0x1a /* BPF_PROG_TYPE_??? */, insn_cnt=2,
> insns=0xafbaa0, license="GPL", log_level=7, log_size=16777215,
> log_buf="\237\353\1", kern_version=KERNEL_VERSION(0, 0, 0),
> prog_flags=0, prog_name="test_main", prog_ifindex=0,
> expected_attach_type=0x19 /* BPF_??? */, prog_btf_fd=6,
> func_info_rec_size=8, func_info=0xafb9f0, func_info_cnt=1,
> line_info_rec_size=16, line_info=0xafba10, line_info_cnt=1, ...}, 120
> ) = ?
> +++ killed by SIGKILL +++
> Killed
>
>
> [79162.619208] BUG: kernel NULL pointer dereference, address:
> 0000000000000000
> [79162.619906] #PF: supervisor read access in kernel mode
> [79162.620582] #PF: error_code(0x0000) - not-present page
> [79162.621255] PGD 80000001e2409067 P4D 80000001e2409067 PUD 22eba9067
> PMD 0
> [79162.621933] Oops: 0000 [#12] SMP PTI
> [79162.622599] CPU: 5 PID: 3191 Comm: xdp_sample_fent Tainted: G D
> 5.4.0+ #3
> [79162.623274] Hardware name: Red Hat KVM, BIOS
> 1.11.1-3.module+el8+2529+a9686a4d 04/01/2014
> [79162.623962] RIP: 0010:bpf_check+0x1648/0x250b
> [79162.624650] Code: 41 89 c5 0f 88 d1 0a 00 00 41 f6 47 02 01 0f 84 17
> 0b 00 00 41 83 7f 04 1a 0f 84 0c 0c 00 00 49 8b 47 20 48 63 db 48 8b 40
> 68 <48> 8b 04 d8 48 8b 40 30 49 89 42 50 49 8b 46 20 4c 89 cf 4c 89 95
> [79162.626088] RSP: 0018:ffffb5f6c07c3c88 EFLAGS: 00010293
> [79162.626822] RAX: 0000000000000000 RBX: 0000000000000000 RCX:
> ffffb5f6c07c3c40
> [79162.627560] RDX: ffffa0a1e6e01818 RSI: 00000000fffffffa RDI:
> 0000000000000000
> [79162.628304] RBP: ffffb5f6c07c3d70 R08: 000000000000000e R09:
> ffffa0a1f5c9dc90
> [79162.629053] R10: ffffa0a1f5c9dc80 R11: ffffa0a1e6e0199a R12:
> ffffa0a1eac48000
> [79162.629806] R13: 0000000000000000 R14: ffffb5f6c043e000 R15:
> ffffb5f6c033f000
> [79162.630562] FS: 00007f560c2e3740(0000) GS:ffffa0a1f7940000(0000)
> knlGS:0000000000000000
> [79162.631324] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [79162.632072] CR2: 0000000000000000 CR3: 00000001e242a005 CR4:
> 0000000000360ee0
> [79162.632813] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [79162.633539] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> 0000000000000400
> [79162.634255] Call Trace:
> [79162.634974] ? _cond_resched+0x15/0x30
> [79162.635686] ? kmem_cache_alloc_trace+0x162/0x220
> [79162.636398] ? selinux_bpf_prog_alloc+0x1f/0x60
> [79162.637111] bpf_prog_load+0x3de/0x690
> [79162.637809] __do_sys_bpf+0x105/0x1740
> [79162.638488] do_syscall_64+0x5b/0x180
> [79162.639147] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [79162.639792] RIP: 0033:0x7f560c3fe1ad
> [79162.640415] Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa
> 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f
> 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d ab 5c 0c 00 f7 d8 64 89 01 48
> [79162.641703] RSP: 002b:00007ffdfbdac318 EFLAGS: 00000202 ORIG_RAX:
> 0000000000000141
> [79162.642363] RAX: ffffffffffffffda RBX: 0000000000afb440 RCX:
> 00007f560c3fe1ad
> [79162.643026] RDX: 0000000000000078 RSI: 00007ffdfbdac390 RDI:
> 0000000000000005
> [79162.643676] RBP: 00007ffdfbdac330 R08: 0000000000afba70 R09:
> 00007ffdfbdac390
> [79162.644310] R10: 0000000000afcf10 R11: 0000000000000202 R12:
> 0000000000402690
> [79162.644935] R13: 00007ffdfbdac790 R14: 0000000000000000 R15:
> 0000000000000000
> [79162.645559] Modules linked in: ip6t_REJECT nf_reject_ipv6
> ip6t_rpfilter ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat
> ebtable_broute ip6table_nat ip6table_mangle ip6table_raw
> ip6table_security iptable_nat nf_nat iptable_mangle iptable_raw
> iptable_security nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set
> nfnetlink ebtable_filter ebtables ip6table_filter ip6_tables
> iptable_filter intel_rapl_msr intel_rapl_common kvm_intel kvm irqbypass
> crct10dif_pclmul crc32_pclmul ghash_clmulni_intel cirrus drm_kms_helper
> virtio_net net_failover joydev drm failover i2c_piix4 virtio_balloon
> pcspkr ip_tables xfs libcrc32c crc32c_intel ata_generic floppy
> virtio_scsi serio_raw pata_acpi qemu_fw_cfg
> [79162.649591] CR2: 0000000000000000
> [79162.650272] ---[ end trace 5119c5364c1e9c83 ]---
> [79162.650957] RIP: 0010:bpf_check+0x1648/0x250b
> [79162.651646] Code: 41 89 c5 0f 88 d1 0a 00 00 41 f6 47 02 01 0f 84 17
> 0b 00 00 41 83 7f 04 1a 0f 84 0c 0c 00 00 49 8b 47 20 48 63 db 48 8b 40
> 68 <48> 8b 04 d8 48 8b 40 30 49 89 42 50 49 8b 46 20 4c 89 cf 4c 89 95
> [79162.653081] RSP: 0018:ffffb5f6c072bc88 EFLAGS: 00010293
> [79162.653807] RAX: 0000000000000000 RBX: 0000000000000000 RCX:
> ffffb5f6c072bc40
> [79162.654536] RDX: ffffa0a1e76b1418 RSI: 00000000fffffffa RDI:
> 0000000000000000
> [79162.655270] RBP: ffffb5f6c072bd70 R08: 000000000000000e R09:
> ffffa0a1e4d3fa90
> [79162.655996] R10: ffffa0a1e4d3fa80 R11: ffffa0a1e76b159a R12:
> ffffa0a1eac7c000
> [79162.656715] R13: 0000000000000000 R14: ffffb5f6c01e3000 R15:
> ffffb5f6c015f000
> [79162.657429] FS: 00007f560c2e3740(0000) GS:ffffa0a1f7940000(0000)
> knlGS:0000000000000000
> [79162.658137] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [79162.658826] CR2: 0000000000000000 CR3: 00000001e242a005 CR4:
> 0000000000360ee0
> [79162.659515] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [79162.660196] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
> 0000000000000400
>
>
> I’ve put my code on GitHub, maybe it’s just something stupid…
>
> https://github.com/chaudron/bpf2bpf-tracing
>
>
> Cheers,
>
> Eelco
>
>
> PS: If I run the latest pahole (v1.15) on the .o files, I get the
> following libbpf error: “libbpf: Cannot find bpf_func_info for main
> program sec fexit/xdp_prog_simple. Ignore all bpf_func_info.”
>
pahole is not supposed to be run on BPF object file. It's needed only
to do DWARF to BTF conversion for kernel itself. So never mind this
one. The NULL dereference, though, seems like a bug, I agree with
Yonghong.
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