[PATCH v5 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 v4:
- Reject the LR and SC instructions themselves in the decode stage
  (riscv_probe_decode_insn()), so a probe placed directly on them is
  caught independently of the kallsyms offset (fixes the case where the
  probe address is exactly the enclosing symbol's start).
- Bound the sequence scan by instruction count (MAX_LRSC_GAP = 16)
  instead of bytes, matching the Zalrsc "at most 16 instructions"
  constraint and avoiding ambiguity with compressed instructions.
- Fold the LR/SC scan into arch_check_kprobe() so the function is walked
  only once; arch_check_kprobe() now returns an error code.
- Use the existing GET_INSN_LENGTH() macro and a single unaligned 32-bit
  load instead of two separate loads.
- Extend the KUnit test to check a probe right before, on the LR, inside,
  on the SC, and right after the sequence, storing absolute probe
  addresses instead of 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   | 24 +++++++
 .../riscv/kernel/tests/kprobes/test-kprobes.c | 26 ++++++++
 .../riscv/kernel/tests/kprobes/test-kprobes.h |  3 +
 6 files changed, 139 insertions(+), 12 deletions(-)

-- 
2.34.1