[PATCH v6 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 v5:
- Fix a dangling stack pointer in the KUnit test: a probe that was
  expected to be rejected but was unexpectedly registered stayed on
  a stack-allocated kprobe.
- Add Acked-by: Masami Hiramatsu to the implementation patch.
- Annotate that test_kprobes_lrsc() is never executed and that
  reject[] must match the length of test_kprobes_lrsc_offsets[].

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                 | 33 ++++++++++
 arch/riscv/kernel/probes/decode-insn.c        |  2 +
 arch/riscv/kernel/probes/kprobes.c            | 63 +++++++++++++++----
 .../kernel/tests/kprobes/test-kprobes-asm.S   | 30 +++++++++
 .../riscv/kernel/tests/kprobes/test-kprobes.c | 31 +++++++++
 .../riscv/kernel/tests/kprobes/test-kprobes.h |  3 +
 6 files changed, 150 insertions(+), 12 deletions(-)

-- 
2.34.1