[RFC 0/4] uprobe,bpf: Allow to change app registers from uprobe

[Jiri Olsa <jolsa@kernel.org>]

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 *RFC* patchset adds support for uprobe program to change app's
registers including instruction pointer.

There's a hiccup with instruction pointer change.. if uprobe handler
changes instruction pointer, the current code will still execute the
original instruction and increment the (new) ip with its length.

This makes the new instruction pointer bogus and application will
likely crash on illegal instruction execution.

I think if user decides to take execution elsewhere, we can skip
original instruction execution (patch#1), but I might be easily
wrong and overlooking something.. hence RFC ;-)

thoughts? thanks,
jirka


---
Jiri Olsa (4):
      uprobe: Do not emulate/sstep original instruction when ip is changed
      bpf: Allow uprobe program to change context registers
      selftests/bpf: Add uprobe context registers changes test
      selftests/bpf: Add uprobe context ip register change test

 include/linux/bpf.h                             |   1 +
 kernel/events/core.c                            |   4 +++
 kernel/events/uprobes.c                         |   3 ++
 kernel/trace/bpf_trace.c                        |   3 +-
 tools/testing/selftests/bpf/prog_tests/uprobe.c | 162 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 tools/testing/selftests/bpf/progs/test_uprobe.c |  38 ++++++++++++++++++++++++
 6 files changed, 208 insertions(+), 3 deletions(-)