[PATCH bpf-next v5 0/3] bpf: Fix tailcall infinite loop caused by freplace

[Leon Hwang <leon.hwang@linux.dev>]

Previously, I fixed a tailcall infinite loop issue caused by trampoline[0].

At this time, I fix a tailcall infinite loop issue caused by tailcall and
freplace combination by preventing updating extended prog to prog_array map
and preventing extending tail callee prog with freplace:

1. If a prog or its subprog has been extended by freplace prog, the prog
   can not be updated to prog_array map.
2. If a prog has been updated to prog_array map, it or its subprog can not
   be extended by freplace prog.

v4 -> v5:
  * Move code of linking/unlinking target prog of freplace to trampoline.c.
  * Address comments from Alexei:
    * Change type of prog_array_member_cnt to u64.
    * Combine two patches to one.

v3 -> v4:
  * Address comments from Eduard:
    * Rename 'tail_callee_cnt' to 'prog_array_member_cnt'.
    * Add comment to 'prog_array_member_cnt'.
    * Use a mutex to protect 'is_extended' and 'prog_array_member_cnt'.

v2 -> v3:
  * Address comments from Alexei:
    * Stop hacking JIT.
    * Prevent the specific use case at attach/update time.

v1 -> v2:
  * Address comment from Eduard:
    * Explain why nop5 and xor/nop3 are swapped at prologue.
  * Address comment from Alexei:
    * Disallow attaching tail_call_reachable freplace prog to
      not-tail_call_reachable target in verifier.
  * Update "bpf, arm64: Fix tailcall infinite loop caused by freplace" with
    latest arm64 JIT code.

Links:
[0] https://lore.kernel.org/bpf/20230912150442.2009-1-hffilwlqm@gmail.com/

Leon Hwang (3):
  bpf: Prevent tailcall infinite loop caused by freplace
  selftests/bpf: Add a test case to confirm a tailcall infinite loop
    issue has been prevented
  selftests/bpf: Add cases to test tailcall in freplace

 include/linux/bpf.h                           |  21 ++
 kernel/bpf/arraymap.c                         |  23 +-
 kernel/bpf/core.c                             |   1 +
 kernel/bpf/syscall.c                          |  21 +-
 kernel/bpf/trampoline.c                       |  43 ++++
 .../selftests/bpf/prog_tests/tailcalls.c      | 196 +++++++++++++++++-
 .../tailcall_bpf2bpf_hierarchy_freplace.c     |  30 +++
 .../testing/selftests/bpf/progs/tc_bpf2bpf.c  |  37 +++-
 8 files changed, 361 insertions(+), 11 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy_freplace.c

-- 
2.44.0