[RFC 0/2] arm64: kprobes: Fix single-step fault and reentry handling

[Pu Hu <hupu@transsion.com>]

From: hupu <hupu@transsion.com>

This series fixes two arm64 kprobes issues observed when running
simpleperf with preemptirq tracepoints and dwarf callchains while a
kprobe is active on a frequently executed kernel function.

The crash happens in the kprobe debug exception path. While a kprobe is
preparing or executing its XOL single-step instruction, perf/trace code
can run in the same window. That code may either take a fault of its own
or hit another kprobe.

Patch 1 makes kprobe_fault_handler() handle a fault in
KPROBE_HIT_SS/KPROBE_REENTER only when the faulting PC points at the
current kprobe's XOL instruction. Otherwise the fault is left to the
normal fault handling path.

Patch 2 allows a kprobe hit in KPROBE_HIT_SS to be handled as a
recoverable one-level reentry. Only a hit while already in
KPROBE_REENTER remains unrecoverable.

This follows the same logic as the existing x86 fixes:
  6381c24cd6d5 ("kprobes/x86: Fix page-fault handling logic")
  6a5022a56ac3 ("kprobes/x86: Allow to handle reentered kprobe on single-stepping")

Reproducer:

  simpleperf record -p <pid> -f 10000 \
    -e preemptirq:preempt_disable \
    -e preemptirq:preempt_enable \
    --duration 9 --call-graph dwarf \
    -o /data/local/tmp/perf.data

Before this series, the crash reproduced frequently. With both patches
applied, it was no longer reproduced in our testing.

hupu (2):
  arm64: kprobes: Do not handle non-XOL faults as kprobe faults
  arm64: kprobes: Allow reentering kprobes while single-stepping

 arch/arm64/kernel/probes/kprobes.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

-- 
2.43.0