[PATCH v5 0/9] livepatch: Introduce replace set support

We previously proposed a BPF+livepatch method to enable rapid
experimentation with new kernel features without interrupting production
workloads:

  https://lore.kernel.org/live-patching/[email protected]/

In the resulting discussion, Song and Petr suggested adding a "replace set"
to support scenarios where specific livepatches can be selectively replaced
or skipped.

This patchset introduces a more flexible model using two new fields in
struct klp_patch:

- provides: an unsigned int id identifying the patch replace set.
  By default (provides=0), any livepatch replaces any other livepatch.

- obsoletes: an optional array of unsigned int ids specifying
  additional provides ids to be replaced. This allows a new patch
  to explicitly obsolete patches from different replace sets.

A new livepatch atomically replaces any existing livepatch whose
provides id matches either:
  1. The new patch provides id (same replace set), or
  2. Any id in the new patch obsoletes list

Additionally, this design deprecates the traditional non-atomic-replace
model. Previously, setting 'replace' to 0 was the only way to keep
certain livepatches persistent on the system, forcing developers to
disable atomic replacement entirely. With the introduction of replace set,
developers now have a selective option to keep specific livepatches
persistent while maintaining atomic replacement capabilities elsewhere.

At present, KLP state, shadow variables, and callbacks are not integrated
with the new replace_set mechanism in this patchset. Support for these
features is deferred until Petr's klp-state-transfer infrastructure is
completed and merged:

  https://github.com/pmladek/linux/tree/klp-state-transfer-v1-iter12

Future Work
===========

- Allow `provides` and `obsoletes` to be configured dynamically at
  module load time, rather than being fixed at build time.

Changes
=======

v4(RFC)->v5:
- Add selftests and Remove the RFC
- Fmprove klp_has_function_conflict() (Song)
- Fix a pre-exisiting bug
- Fix bugs reported by sashiko

v4 (RFC): https://lore.kernel.org/live-patching/[email protected]/

v3->v4(RFC):
- Allow a livepatch to replace livepatches with different provides IDs.
  Replace the single `replace_set` field with two separate fields,
  `provides` and `obsoletes`, for more flexible replacement semantics.
  (Petr, Joe)

v3: https://lore.kernel.org/live-patching/[email protected]/

v2->v3:
- Address the feedback from Sachiko AI
 - Fix the pre-existing NULL pointer dereference issue
 - Move klp_find_func into core.h
 - Don't deprecate stack_order completely

v2: https://lore.kernel.org/live-patching/[email protected]/

v1->v2:
- Incorporate feedback from Petr:
  - Initialize replace_set to 0 by default
  - Improve documentation
  - Enforce that livepatches in different replace_sets cannot use the same
    state->id.
  - Enforce that livepatches in different replace_sets cannot modify the
    same function.
  - Ensure consistent capitalization and naming usage of KLP_REPLACE_SET.
- Incorporate feedback from Sachiko AI:
  - Skip the klp_transition patch during klp_force_transition().

v1 (RFC): https://lore.kernel.org/live-patching/[email protected]/

Yafang Shao (9):
  livepatch: Fix wrong index in funcs cleanup error path
  livepatch: Make klp_find_func() non static
  livepatch: Call klp_init_patch_early() earlier
  livepatch: Implement replace set for scoped atomic replace
  livepatch: Deprecate stack_order
  selftests: livepatch: Adapt atomic replace tests to provides/obsoletes
  selftests: livepatch: Add provides/obsoletes test scenarios
  selftests: livepatch: Add test for state ID conflict across provides
  selftests: livepatch: Add test for function conflict across provides

 .../ABI/removed/sysfs-kernel-livepatch        |  16 +
 .../ABI/testing/sysfs-kernel-livepatch        |  27 +-
 .../livepatch/cumulative-patches.rst          |  93 ++--
 Documentation/livepatch/livepatch.rst         |  23 +-
 include/linux/livepatch.h                     |   7 +-
 kernel/livepatch/core.c                       | 114 +++--
 kernel/livepatch/core.h                       |   2 +
 kernel/livepatch/state.c                      |  57 ++-
 kernel/livepatch/transition.c                 |  11 +-
 scripts/livepatch/init.c                      |  71 +++-
 scripts/livepatch/klp-build                   |  77 +++-
 tools/testing/selftests/livepatch/Makefile    |   3 +-
 .../testing/selftests/livepatch/functions.sh  |  15 +
 .../selftests/livepatch/test-callbacks.sh     |   6 +
 .../selftests/livepatch/test-livepatch.sh     |   6 +
 .../livepatch/test-provides-obsoletes.sh      | 401 ++++++++++++++++++
 .../selftests/livepatch/test_modules/Makefile |  11 +
 .../test_modules/test_klp_atomic_replace.c    |  22 +
 .../test_modules/test_klp_callbacks_demo2.c   |  12 +
 .../test_modules/test_klp_livepatch.c         |   9 +
 .../test_modules/test_klp_provides.c          |  72 ++++
 .../livepatch/test_modules/test_klp_state.c   |  13 +
 .../livepatch/test_modules/test_klp_state2.c  |  23 +
 23 files changed, 968 insertions(+), 123 deletions(-)
 create mode 100644 Documentation/ABI/removed/sysfs-kernel-livepatch
 create mode 100755 tools/testing/selftests/livepatch/test-provides-obsoletes.sh
 create mode 100644 tools/testing/selftests/livepatch/test_modules/test_klp_provides.c

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2.52.0