Re: [PATCHv3 perf/core 0/6] uprobe,bpf: Allow to change app registers from uprobe registers

[Ihor Solodrai <ihor.solodrai@linux.dev>]

On 9/12/25 1:55 PM, Jiri Olsa wrote:
> On Fri, Sep 12, 2025 at 01:28:55PM -0700, Ihor Solodrai wrote:
>> On 9/9/25 9:41 AM, Andrii Nakryiko wrote:
>>> On Tue, Sep 9, 2025 at 8:39 AM Jiri Olsa <jolsa@kernel.org> wrote:
>>>>
>>>> hi,
>>>> we recently had several requests for tetragon to be able to change
>>>> user application function return value or divert its execution through
>>>> instruction pointer change.
>>>>
>>>> This patchset adds support for uprobe program to change app's registers
>>>> including instruction pointer.
>>>>
>>>> v3 changes:
>>>> - deny attach of kprobe,multi with kprobe_write_ctx set [Alexei]
>>>> - added more tests for denied kprobe attachment
>>>>
>>>> thanks,
>>>> jirka
>>>>
>>>>
>>>> ---
>>>> Jiri Olsa (6):
>>>>         bpf: Allow uprobe program to change context registers
>>>>         uprobe: Do not emulate/sstep original instruction when ip is changed
>>>>         selftests/bpf: Add uprobe context registers changes test
>>>>         selftests/bpf: Add uprobe context ip register change test
>>>>         selftests/bpf: Add kprobe write ctx attach test
>>>>         selftests/bpf: Add kprobe multi write ctx attach test
>>>>
>>>
>>> For the series:
>>>
>>> Acked-by: Andrii Nakryiko <andrii@kernel.org>
>>>
>>> Question is which tree will this go through? Most changes are in BPF,
>>> so probably bpf-next, right?
>>
>> Hi Jiri.
>>
>> This series does not apply to current bpf-next, see below.
>>
>> Could you please respin it with bpf-next tag?
>> E.g. "[PATCH v4 bpf-next 0/6] ..."
>>
> 
> hi,
> the uprobe change it needs to be on top of the optimized uprobes (tip/perf/core)
> but the bpf selftests patches could be applied on bpf-next/master and disabled
> in CI until tip/perf/core changes are merged in?

Currently the series isn't even picked up by CI properly because it
doesn't apply. It's not that the tests are failing.

If there is a dependency on external (to bpf-next) commit, we could
add it as a temporary CI patch or just wait for it to be merged in.

But if you can make this series applicable to bpf-next without
tip/perf/core changes, you can do that and add relevant tests to
`tools/testing/selftests/bpf/DENYLIST`. It's important to not forget
to remove them later though.

> 
> thanks,
> jirka
> 
> 
>> Thanks!
>>
>> $ git log -1 --oneline
>> a578b54a8ad2 (HEAD -> master, origin/master, origin/HEAD,
>> kernel-patches/bpf-next) Merge branch
>> 'bpf-report-arena-faults-to-bpf-streams'
>> $ b4 am 20250909123857.315599-1-jolsa@kernel.org
>> [...]
>> $ git am ./v3_20250909_jolsa_uprobe_bpf_allow_to_change_app_registers_from_uprobe_registers.mbx
>> Applying: bpf: Allow uprobe program to change context registers
>> Applying: uprobe: Do not emulate/sstep original instruction when ip is
>> changed
>> error: patch failed: kernel/events/uprobes.c:2768
>> error: kernel/events/uprobes.c: patch does not apply
>> Patch failed at 0002 uprobe: Do not emulate/sstep original instruction when
>> ip is changed
>> [...]
>>
>>>
>>>>    include/linux/bpf.h                                        |   1 +
>>>>    kernel/events/core.c                                       |   4 +++
>>>>    kernel/events/uprobes.c                                    |   7 +++++
>>>>    kernel/trace/bpf_trace.c                                   |   7 +++--
>>>>    tools/testing/selftests/bpf/prog_tests/attach_probe.c      |  28 +++++++++++++++++
>>>>    tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c |  27 ++++++++++++++++
>>>>    tools/testing/selftests/bpf/prog_tests/uprobe.c            | 156 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>>>    tools/testing/selftests/bpf/progs/kprobe_write_ctx.c       |  22 +++++++++++++
>>>>    tools/testing/selftests/bpf/progs/test_uprobe.c            |  38 +++++++++++++++++++++++
>>>>    9 files changed, 287 insertions(+), 3 deletions(-)
>>>>    create mode 100644 tools/testing/selftests/bpf/progs/kprobe_write_ctx.c
>>