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linux-next/kernel/bpf
Yonghong Song d36216429f bpf: Emit better log message if bpf_iter ctx arg btf_id == 0
To avoid kernel build failure due to some missing .BTF-ids referenced
functions/types, the patch ([1]) tries to fill btf_id 0 for
these types.

In bpf verifier, for percpu variable and helper returning btf_id cases,
verifier already emitted proper warning with something like
  verbose(env, "Helper has invalid btf_id in R%d\n", regno);
  verbose(env, "invalid return type %d of func %s#%d\n",
          fn->ret_type, func_id_name(func_id), func_id);

But this is not the case for bpf_iter context arguments.
I hacked resolve_btfids to encode btf_id 0 for struct task_struct.
With `./test_progs -n 7/5`, I got,
  0: (79) r2 = *(u64 *)(r1 +0)
  func 'bpf_iter_task' arg0 has btf_id 29739 type STRUCT 'bpf_iter_meta'
  ; struct seq_file *seq = ctx->meta->seq;
  1: (79) r6 = *(u64 *)(r2 +0)
  ; struct task_struct *task = ctx->task;
  2: (79) r7 = *(u64 *)(r1 +8)
  ; if (task == (void *)0) {
  3: (55) if r7 != 0x0 goto pc+11
  ...
  ; BPF_SEQ_PRINTF(seq, "%8d %8d\n", task->tgid, task->pid);
  26: (61) r1 = *(u32 *)(r7 +1372)
  Type '(anon)' is not a struct

Basically, verifier will return btf_id 0 for task_struct.
Later on, when the code tries to access task->tgid, the
verifier correctly complains the type is '(anon)' and it is
not a struct. Users still need to backtrace to find out
what is going on.

Let us catch the invalid btf_id 0 earlier
and provide better message indicating btf_id is wrong.
The new error message looks like below:
  R1 type=ctx expected=fp
  ; struct seq_file *seq = ctx->meta->seq;
  0: (79) r2 = *(u64 *)(r1 +0)
  func 'bpf_iter_task' arg0 has btf_id 29739 type STRUCT 'bpf_iter_meta'
  ; struct seq_file *seq = ctx->meta->seq;
  1: (79) r6 = *(u64 *)(r2 +0)
  ; struct task_struct *task = ctx->task;
  2: (79) r7 = *(u64 *)(r1 +8)
  invalid btf_id for context argument offset 8
  invalid bpf_context access off=8 size=8

[1] https://lore.kernel.org/bpf/20210727132532.2473636-1-hengqi.chen@gmail.com/

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210728183025.1461750-1-yhs@fb.com
2021-07-29 15:10:11 -07:00
..
preload libbpf: Move BPF_SEQ_PRINTF and BPF_SNPRINTF to bpf_helpers.h 2021-05-26 10:45:41 -07:00
arraymap.c bpf: Add map side support for bpf timers. 2021-07-15 22:31:10 +02:00
bpf_inode_storage.c bpf: Fix spelling mistakes 2021-05-24 21:13:05 -07:00
bpf_iter.c bpf: tcp: Support bpf_(get|set)sockopt in bpf tcp iter 2021-07-23 16:45:07 -07:00
bpf_local_storage.c bpf: Prevent deadlock from recursive bpf_task_storage_[get|delete] 2021-02-26 11:51:48 -08:00
bpf_lru_list.c bpf_lru_list: Read double-checked variable once without lock 2021-02-10 15:54:26 -08:00
bpf_lru_list.h bpf: Fix a typo "inacitve" -> "inactive" 2020-04-06 21:54:10 +02:00
bpf_lsm.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2021-06-17 11:54:56 -07:00
bpf_struct_ops_types.h bpf: tcp: Support tcp_congestion_ops in bpf 2020-01-09 08:46:18 -08:00
bpf_struct_ops.c bpf: Fix fexit trampoline. 2021-03-18 00:22:51 +01:00
bpf_task_storage.c bpf: Make symbol 'bpf_task_storage_busy' static 2021-03-16 12:24:20 -07:00
btf.c bpf: Emit better log message if bpf_iter ctx arg btf_id == 0 2021-07-29 15:10:11 -07:00
cgroup.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2021-02-16 13:14:06 -08:00
core.c bpf: Track subprog poke descriptors correctly and fix use-after-free 2021-07-09 12:08:27 +02:00
cpumap.c bpf: cpumap: Implement generic cpumap 2021-07-07 20:01:45 -07:00
devmap.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2021-07-15 22:40:10 -07:00
disasm.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2021-04-09 20:48:35 -07:00
disasm.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 295 2019-06-05 17:36:38 +02:00
dispatcher.c bpf: Remove bpf_image tree 2020-03-13 12:49:52 -07:00
hashtab.c bpf: Add map side support for bpf timers. 2021-07-15 22:31:10 +02:00
helpers.c bpf: Add ambient BPF runtime context stored in current 2021-07-16 21:15:28 +02:00
inode.c bpf: Fix regression on BPF_OBJ_GET with non-O_RDWR flags 2021-06-22 14:57:43 +02:00
Kconfig sock_map: Relax config dependency to CONFIG_NET 2021-07-15 18:17:49 -07:00
local_storage.c bpf: Increase supported cgroup storage value size 2021-07-27 15:59:29 -07:00
lpm_trie.c bpf: Allow RCU-protected lookups to happen from bh context 2021-06-24 19:41:15 +02:00
Makefile bpf: Enable task local storage for tracing programs 2021-02-26 11:51:47 -08:00
map_in_map.c bpf: Remember BTF of inner maps. 2021-07-15 22:31:10 +02:00
map_in_map.h bpf: Add map_meta_equal map ops 2020-08-28 15:41:30 +02:00
map_iter.c bpf: Implement link_query callbacks in map element iterators 2020-08-21 14:01:39 -07:00
net_namespace.c bpf: Add support for forced LINK_DETACH command 2020-08-01 20:38:28 -07:00
offload.c bpf, offload: Replace bitwise AND by logical AND in bpf_prog_offload_info_fill 2020-02-17 16:53:49 +01:00
percpu_freelist.c bpf: Use raw_spin_trylock() for pcpu_freelist_push/pop in NMI 2020-10-06 00:04:11 +02:00
percpu_freelist.h bpf: Use raw_spin_trylock() for pcpu_freelist_push/pop in NMI 2020-10-06 00:04:11 +02:00
prog_iter.c bpf: Refactor bpf_iter_reg to have separate seq_info member 2020-07-25 20:16:32 -07:00
queue_stack_maps.c bpf: Eliminate rlimit-based memory accounting for queue_stack_maps maps 2020-12-02 18:32:46 -08:00
reuseport_array.c bpf: Fix spelling mistakes 2021-05-24 21:13:05 -07:00
ringbuf.c bpf: Fix false positive kmemleak report in bpf_ringbuf_area_alloc() 2021-06-28 15:57:46 +02:00
stackmap.c bpf: Refcount task stack in bpf_get_task_stack 2021-04-01 13:58:07 -07:00
syscall.c bpf: Add map side support for bpf timers. 2021-07-15 22:31:10 +02:00
sysfs_btf.c bpf: Load and verify kernel module BTFs 2020-11-10 15:25:53 -08:00
task_iter.c bpf: Introduce task_vma bpf_iter 2021-02-12 12:56:53 -08:00
tnum.c bpf, tnums: Provably sound, faster, and more precise algorithm for tnum_mul 2021-06-01 13:34:15 +02:00
trampoline.c bpf: Enable BPF_TRAMP_F_IP_ARG for trampolines with call_get_func_ip 2021-07-15 17:16:06 -07:00
verifier.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2021-07-15 22:40:10 -07:00