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bpf: Remove OUTPUT_SKB&HAS_KPROBE_MULTI macros #455

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merged 4 commits into from
Nov 19, 2024

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Asphaltt
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When call set_skb_btf() or set_shinfo_btf(), these functions are protected by constant CFG.

Then, while loading kprobe_pwru into kernel, if no --output-skb/--output-skb-shared-info, set_skb_btf()/set_shinfo_btf() won't be verified. Next, these unreachable code will be eliminated by verifier.

@Asphaltt Asphaltt changed the title bpf: Remove unnecessary OUTPUT_SKB macro bpf: Remove OUTPUT_SKB&HAS_KPROBE_MULTI macros Nov 10, 2024
@jschwinger233
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Just for the record:

  1. 6.1 and bpf-next see pwru --backend kprobe-multi broken while --backend kprobe stil works.
  2. 5.4 fails due to CO-RE issues on sk_buff. My guess is some members are deleted / renamed between 5.4 and 5.15.

@Asphaltt Asphaltt force-pushed the feat/simplify-build branch 2 times, most recently from f93ebd2 to 194dbff Compare November 12, 2024 14:57
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@jschwinger233 jschwinger233 left a comment

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Always love to see code simplification! Left some comments to discuss.

internal/pwru/btf.go Show resolved Hide resolved
bpf/features.c Outdated Show resolved Hide resolved
bpf/features.c Outdated Show resolved Hide resolved
It's to avoid the following issue for next commit, especially on Ubuntu
20.04:

 ; instruction poisoned by CO-RE
 938: (85) call unknown#195896080
 invalid func unknown#195896080
 processed 519 insns (limit 1000000) max_states_per_insn 0 total_states 29 peak_states 29 mark_read 27

Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>
When call set_skb_btf() or set_shinfo_btf(), these functions are
protected by constant CFG.

Then, while loading kprobe_pwru into kernel, if no
--output-skb/--output-skb-shared-info, set_skb_btf()/set_shinfo_btf()
won't be verified. Next, these unreachable code will be eliminated by
verifier.

Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>
Simplify bpf code.

And use Go to determine loading kprobe or kprobe.multi bpf prog.

Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>
Fix this panic:

$ sudo ./pwru --output-tuple 'dst host 1.0.0.1 and port 8080'
2024/11/12 13:58:41 Attaching kprobes (via kprobe)...
102 / 1255 [---------->_________________________________________________________________________________________________________________________] 8.13% 96 p/s
231 / 1255 [----------------------->__________________________________________________________________________________________________________] 18.41% 120 p/s
2024/11/12 13:58:43 Listening for events..
SKB                CPU PROCESS          NETNS      MARK/x        IFACE       PROTO  MTU   LEN   TUPLE FUNC
2024/11/12 13:58:43 Received signal, exiting program..
2024/11/12 13:58:43 Detaching kprobes...
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x6675d8]

goroutine 1 [running]:
github.com/cilium/pwru/internal/pwru.(*kprober).DetachKprobes(0x0)
	/root/Projects/leonhwang/pwru/internal/pwru/kprobe.go:130 +0xb8
main.main()
	/root/Projects/leonhwang/pwru/main.go:322 +0x2013

Signed-off-by: Leon Hwang <hffilwlqm@gmail.com>
@Asphaltt Asphaltt marked this pull request as ready for review November 14, 2024 02:31
@Asphaltt Asphaltt requested a review from a team as a code owner November 14, 2024 02:31
@Asphaltt Asphaltt requested review from brb and removed request for a team November 14, 2024 02:31
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Thanks!

@brb brb merged commit dbaa406 into cilium:main Nov 19, 2024
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3 participants