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ftrace_direct (used by bpf trampoline) conflicts with live patch #237

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ftrace_direct (used by bpf trampoline) conflicts with live patch #237

wants to merge 2 commits into from

Commits on Apr 1, 2022

  1. adding ci files

    Nobody committed Apr 1, 2022
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  2. ftrace_direct (used by bpf trampoline) conflicts with live patch 

    Hi Steven,

We hit an issue with bpf trampoline and kernel live patch on the
same function.

Basically, we have tracing and live patch on the same function.
If we use kprobe (over ftrace) for tracing, it works fine with
live patch. However, fentry on the same function does not work
with live patch (the one comes later fails to attach).

After digging into this, I found this is because bpf trampoline
uses register_ftrace_direct, which enables IPMODIFY by default.
OTOH, it seems that BPF doesn't really need IPMODIFY. As BPF
trampoline does a "goto do_fexit" in jit for BPF_TRAMP_MODIFY_RETURN.

IIUC, we can let bpf trampoline and live patch work together with
an ipmodify-less version of register_ftrace_direct, like attached
below.

Does this make sense to you? Did I miss something?

Thanks in advance,
Song
    @liu-song-6
    liu-song-6 authored and Nobody committed Apr 1, 2022
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