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

On 9/12/25 1:55 PM, Jiri Olsa wrote:

On Fri, Sep 12, 2025 at 01:28:55PM -0700, Ihor Solodrai wrote:

quoted

On 9/9/25 9:41 AM, Andrii Nakryiko wrote:

quoted

On Tue, Sep 9, 2025 at 8:39 AM Jiri Olsa [off-list ref] wrote:

quoted

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

quoted

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
[...]

quoted

quoted

   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