arm64: kprobes: Use BRK instead of single-step when executing instructions out-of...

arm64: kprobes: Use BRK instead of single-step when executing instructions out-of-line

Commit 8f804e0f5bdd ("kprobes: Init kprobes in early_initcall") enabled
using kprobes from early_initcall. Unfortunately at this point the
hardware debug infrastructure is not operational. The OS lock may still
be locked, and the hardware watchpoints may have unknown values when
kprobe enables debug monitors to single-step instructions.

Rather than using hardware single-step, append a BRK instruction after
the instruction to be executed out-of-line.

Fixes: 8f804e0f5bdd ("kprobes: Init kprobes in early_initcall")
Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20201103134900.337243-1-jean-philippe@linaro.org
Signed-off-by: Will Deacon <will@kernel.org>