On Mon, Nov 30, 2020 at 7:49 PM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>
> Implement libbpf support for performing CO-RE relocations against types in
> kernel module BTFs, in addition to existing vmlinux BTF support.
>
> This is a first step towards fully supporting kernel module BTFs. Subsequent
> patch sets will expand kernel and libbpf sides to allow using other
> BTF-powered capabilities (fentry/fexit, struct_ops, ksym externs, etc). For
> CO-RE relocations support, though, no extra kernel changes are necessary.
>
> This patch set also sets up a convenient and fully-controlled custom kernel
> module (called "bpf_testmod"), that is a predictable playground for all the
> BPF selftests, that rely on module BTFs.
>
> v2->v3:
> - fix subtle uninitialized variable use in BTF ID iteration code;
While testing this patch I've hit this:
#111 test_bpffs:OK
[ 222.418122] 9pnet_virtio: no channels available for device hostshare0
[ 222.688972] sysfs: cannot create duplicate filename '/kernel/btf/bpf_preload'
[ 222.689811] CPU: 0 PID: 2485 Comm: modprobe Tainted: G O
5.10.0-rc3-00874-gfe521960f79f #3078
[ 222.690813] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.11.0-2.el7 04/01/2014
[ 222.691681] Call Trace:
[ 222.691937] dump_stack+0x9a/0xcc
[ 222.692303] sysfs_warn_dup.cold+0x17/0x24
[ 222.692714] sysfs_add_file_mode_ns+0x38c/0x560
[ 222.693200] sysfs_create_bin_file+0xf8/0x150
[ 222.693635] ? sysfs_add_file_to_group+0x150/0x150
[ 222.694140] ? __kasan_kmalloc.constprop.0+0xc2/0xd0
[ 222.694648] btf_module_notify+0x6ac/0xd30
[ 222.695111] notifier_call_chain_robust+0xa6/0x1a0
[ 222.695658] blocking_notifier_call_chain_robust+0x61/0x90
[ 222.696251] load_module+0x62da/0x9f40
[ 222.696627] ? rcu_read_lock_sched_held+0x81/0xb0
[ 222.697156] ? module_frob_arch_sections+0x20/0x20
[ 222.697632] ? ima_read_file+0x140/0x140
[ 222.698027] ? security_kernel_post_read_file+0x68/0xb0
[ 222.698643] ? __do_sys_finit_module+0xf7/0x150
[ 222.699126] __do_sys_finit_module+0xf7/0x150
[ 222.699588] ? __ia32_sys_init_module+0xa0/0xa0
[ 222.700049] ? bpf_prog_32007c34f7726d29_bpf_prog1+0x198/0x7ec
[ 222.700690] ? rcu_read_lock_bh_held+0x90/0x90
[ 222.701161] ? __bpf_trace_sys_enter+0x4f/0x60
[ 222.701601] ? syscall_trace_enter.isra.0+0x174/0x230
[ 222.702123] do_syscall_64+0x2d/0x40
[ 222.702483] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 222.703002] RIP: 0033:0x7fd909d727f9
[ 222.703385] Code: 00 f3 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40
00 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 57 76 2b 00 f7 d8 64 89
01 48
[ 222.705258] RSP: 002b:00007ffeecdb8e28 EFLAGS: 00000206 ORIG_RAX:
0000000000000139
[ 222.706010] RAX: ffffffffffffffda RBX: 0000000000625380 RCX: 00007fd909d727f9
[ 222.706778] RDX: 0000000000000000 RSI: 000000000041a213 RDI: 0000000000000000
[ 222.707522] RBP: 000000000041a213 R08: 0000000000000000 R09: 00000000006242a0
[ 222.708241] R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
[ 222.708932] R13: 0000000000625530 R14: 0000000000040000 R15: 0000000000625380
[ 222.709715] failed to register module [bpf_preload] BTF in sysfs: -17
[ 222.892778] sysfs: cannot create duplicate filename '/kernel/btf/bpf_testmod'
[ 222.893609] CPU: 2 PID: 2493 Comm: test_progs Tainted: G
O 5.10.0-rc3-00874-gfe521960f79f #3078
[ 222.894622] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.11.0-2.el7 04/01/2014
[ 222.895498] Call Trace:
[ 222.895768] dump_stack+0x9a/0xcc
[ 222.896128] sysfs_warn_dup.cold+0x17/0x24
[ 222.896573] sysfs_add_file_mode_ns+0x38c/0x560
[ 222.897047] sysfs_create_bin_file+0xf8/0x150
[ 222.897506] ? sysfs_add_file_to_group+0x150/0x150
[ 222.898004] ? __kasan_kmalloc.constprop.0+0xc2/0xd0
[ 222.898524] btf_module_notify+0x6ac/0xd30
[ 222.898968] notifier_call_chain_robust+0xa6/0x1a0
[ 222.899477] blocking_notifier_call_chain_robust+0x61/0x90
[ 222.900040] load_module+0x62da/0x9f40
[ 222.900434] ? rcu_read_lock_sched_held+0x81/0xb0
[ 222.900951] ? module_frob_arch_sections+0x20/0x20
[ 222.901474] ? ima_read_file+0x140/0x140
[ 222.901881] ? security_kernel_post_read_file+0x68/0xb0
[ 222.902450] ? __do_sys_finit_module+0xf7/0x150
[ 222.902937] __do_sys_finit_module+0xf7/0x150
[ 222.903401] ? __ia32_sys_init_module+0xa0/0xa0
[ 222.903867] ? bpf_prog_32007c34f7726d29_bpf_prog1+0x198/0x7ec
[ 222.904480] ? rcu_read_lock_bh_held+0x90/0x90
[ 222.904935] ? __bpf_trace_sys_enter+0x4f/0x60
[ 222.905401] ? syscall_trace_enter.isra.0+0x174/0x230
[ 222.905925] do_syscall_64+0x2d/0x40
[ 222.906304] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 222.906818] RIP: 0033:0x7fd58327e7f9
[ 222.907193] Code: 00 f3 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40
00 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 57 76 2b 00 f7 d8 64 89
01 48
[ 222.909049] RSP: 002b:00007ffce1e96fe8 EFLAGS: 00000246 ORIG_RAX:
0000000000000139
[ 222.909823] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fd58327e7f9
[ 222.910541] RDX: 0000000000000000 RSI: 000000000165481f RDI: 0000000000000004
[ 222.911260] RBP: 0000000000000004 R08: 00007ffce1e97230 R09: 0000000000000000
[ 222.911995] R10: 0000000000002011 R11: 0000000000000246 R12: 0000000000000000
[ 222.912710] R13: 00007ffce1e97230 R14: 0000000000000000 R15: 0000000000000000
[ 222.913503] failed to register module [bpf_testmod] BTF in sysfs: -17
