[PATCH v2 0/4] openrisc: Add support for KProbes

[Sahil Siddiq]

Hi,

Apologies for the delay. This is v2 of the patch series to add KProbe
support for OpenRISC.

The series also adds support for Kretprobes (which depends on the rethook
framework [1]). Kretprobes are fired on function return.

In order to build the kernel with Kprobes and Kretprobes enabled, the
following config options are required:
1. CONFIG_HAVE_KPROBES=y
2. CONFIG_KPROBES=y
3. CONFIG_RETHOOK=y
4. CONFIG_KRETPROBES=y

I tested the generic functionality of Kprobes and Kretprobes using the
tests located at "lib/tests" [2], samples located at "samples/kprobes" [3],
as well as a few test modules that I have published here [4]. The following
options are required to build the samples and tests:
1. CONFIG_SAMPLES=y
2. CONFIG_SAMPLE_KPROBES=m
3. CONFIG_SAMPLE_KRETPROBES=m
4. CONFIG_KPROBES_SANITY_TEST=m

I have also added unit tests at "arch/openrisc/kernel/tests" to verify
that Kprobes work properly when inserted at branch instructions, and
that delay slots are handled correctly. The tests are based on the Kprobe
testsuite added for RISC-V. The following options need to be enabled to
build the tests:
1. CONFIG_KUNIT=y
2. CONFIG_RUNTIME_KERNEL_TESTING_MENU=y
3. CONFIG_OR_KPROBES_KUNIT=m

Below are the results of the tests and sample modules when run in my
environment.

- kretprobe_example:

/home # insmod kretprobe_example.ko 
Planted return probe at kernel_clone: (ptrval)
/home # ls >/dev/null
kernel_clone returned 35 and took 1302450 ns to execute
/home # rmmod kretprobe_example.ko 
kernel_clone returned 36 and took 1121200 ns to execute
kretprobe at (ptrval) unregistered
Missed probing 0 instances of kernel_clone

- test_kprobes:

/home # insmod test_kprobes.ko 
KTAP version 1
1..1
    KTAP version 1
    # Subtest: kprobes_test
    # module: test_kprobes
    1..5
    ok 1 test_kprobe
    ok 2 test_kprobes
    ok 3 test_kprobe_missed
    ok 4 test_kretprobe
    ok 5 test_kretprobes
# kprobes_test: pass:5 fail:0 skip:0 total:5
# Totals: pass:5 fail:0 skip:0 total:5
ok 1 kprobes_test

- openrisc_test_kprobes:

/home # insmod openrisc_test_kprobes.ko 
KTAP version 1
1..1
    KTAP version 1
    # Subtest: kprobes_openrisc
    # module: openrisc_test_kprobes
    1..1
    ok 1 test_kprobe_openrisc
ok 1 kprobes_openrisc

I have also made changes based on the review comments I received for
v1 [5] including several of Sachiko's comments [6]. I chose not to make
changes in a few places. I'll send emails as a reply to this thread
explaining my reasoning inline.

Thanks,
Sahil

[1] https://lkml.rescloud.iu.edu/2203.0/05974.html
[2] https://github.com/torvalds/linux/tree/master/lib/tests
[3] https://github.com/torvalds/linux/tree/master/samples/kprobes
[4] https://github.com/valdaarhun/or-dev
[5] https://lwn.net/ml/all/20260407185650.79816-1-sahilcdq0@xxxxxxxxx/
[6] https://sashiko.dev/#/patchset/20260407185650.79816-1-sahilcdq0%40gmail.com

Sahil Siddiq (4):
  openrisc: Add utilities and clean up simulation of instructions
  openrisc: Add KProbes
  openrisc: Add unit tests for KProbes on branch instructions
  openrisc: Add Kretprobes

 arch/openrisc/Kconfig                         |   3 +
 arch/openrisc/Kconfig.debug                   |  30 +-
 arch/openrisc/configs/or1ksim_defconfig       |   2 +
 arch/openrisc/configs/virt_defconfig          |   2 +
 arch/openrisc/include/asm/asm.h               |  22 +
 arch/openrisc/include/asm/break.h             |  19 +
 arch/openrisc/include/asm/cpuinfo.h           |   3 +
 arch/openrisc/include/asm/insn-def.h          |  64 ++-
 arch/openrisc/include/asm/kprobes.h           |  77 ++++
 arch/openrisc/include/asm/spr_defs.h          |   1 +
 arch/openrisc/kernel/Makefile                 |   5 +-
 arch/openrisc/kernel/entry.S                  |  16 +
 arch/openrisc/kernel/insn.c                   |  84 ++++
 arch/openrisc/kernel/kprobes.c                | 400 ++++++++++++++++++
 arch/openrisc/kernel/rethook.c                |  32 ++
 arch/openrisc/kernel/rethook.h                |   8 +
 arch/openrisc/kernel/rethook_trampoline.S     |  97 +++++
 arch/openrisc/kernel/setup.c                  |   4 +
 arch/openrisc/kernel/tests/Makefile           |   3 +
 arch/openrisc/kernel/tests/test_kprobes.c     |  59 +++
 arch/openrisc/kernel/tests/test_kprobes.h     |  24 ++
 arch/openrisc/kernel/tests/test_kprobes_asm.S | 147 +++++++
 arch/openrisc/kernel/traps.c                  |  82 ++--
 arch/openrisc/lib/memcpy.c                    |   2 +
 arch/openrisc/lib/memset.S                    |   4 +
 arch/openrisc/mm/fault.c                      |   5 +
 samples/kprobes/kprobe_example.c              |   8 +
 27 files changed, 1152 insertions(+), 51 deletions(-)
 create mode 100644 arch/openrisc/include/asm/asm.h
 create mode 100644 arch/openrisc/include/asm/break.h
 create mode 100644 arch/openrisc/include/asm/kprobes.h
 create mode 100644 arch/openrisc/kernel/insn.c
 create mode 100644 arch/openrisc/kernel/kprobes.c
 create mode 100644 arch/openrisc/kernel/rethook.c
 create mode 100644 arch/openrisc/kernel/rethook.h
 create mode 100644 arch/openrisc/kernel/rethook_trampoline.S
 create mode 100644 arch/openrisc/kernel/tests/Makefile
 create mode 100644 arch/openrisc/kernel/tests/test_kprobes.c
 create mode 100644 arch/openrisc/kernel/tests/test_kprobes.h
 create mode 100644 arch/openrisc/kernel/tests/test_kprobes_asm.S

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2.55.0