[PATCH v7 0/2] riscv: kprobes: reject probes inside LR/SC sequences

[Xiaofeng Yuan <yuanxiaofeng@eswincomputing.com>]

A breakpoint trap taken in the middle of an LR/SC sequence clears the
load reservation, so an SC following the probed instruction always fails
and the enclosing retry loop re-enters the breakpoint, livelocking the
CPU.  This series makes the RISC-V kprobes implementation reject probes
placed on an LR/SC instruction or between them, following arm64's
approach for its equivalent exclusive load/store instructions.

Changes since v6:
- Fix an off-by-one in the LR/SC tracking window: a constrained loop
  holds at most 16 instructions (the LR, the SC, and up to 14 between
  them), and the walk now stops tracking after 14 intermediate
  instructions, as the spec requires.
- Use the existing RV_EXTRACT_FUNCT3()/RV_EXTRACT_RS2_REG() helpers and
  add RV_EXTRACT_FUNCT5() in riscv_insn_is_lr()/riscv_insn_is_sc() to
  avoid code duplication.
- Rename test_kprobes_lrsc_offsets[] and split it into separate
  test_kprobes_lrsc_allowed_addresses[]/test_kprobes_lrsc_rejected_
  addresses[] so that adding an entry does not force a change in a
  parallel reject[] table.
- Add a KUnit boundary case pinning the 16-instruction tracking window:
  the 15th instruction after an LR must be rejected and the 16th must be
  accepted (this fails without the off-by-one fix).

Verified by cross-compiling for RISC-V and running the kprobes KUnit
test in QEMU (ok 2 kprobes_riscv).

Xiaofeng Yuan (2):
  riscv: kprobes: reject probes inside LR/SC sequences
  riscv: kprobes: add KUnit test for LR/SC sequence rejection

 arch/riscv/include/asm/insn.h                 | 63 ++++++++++++++----
 arch/riscv/kernel/probes/decode-insn.c        |  2 +
 arch/riscv/kernel/probes/kprobes.c            | 65 +++++++++++++++----
 .../kernel/tests/kprobes/test-kprobes-asm.S   | 60 +++++++++++++++++
 .../riscv/kernel/tests/kprobes/test-kprobes.c | 34 ++++++++++
 .../riscv/kernel/tests/kprobes/test-kprobes.h |  6 ++
 6 files changed, 207 insertions(+), 23 deletions(-)

-- 
2.34.1