The livepatch consistency model requires reliable stack tracing architecture support in order to work properly. In order to achieve this, two main issues have to be solved. First, reliable and consistent call chain backtracing has to be ensured. Second, the unwinder needs to be able to detect stack corruptions and return errors. The former should be guaranteed (see 3/3 for details), the latter is implemented by the patch set (mainly 3/3). It passes livepatch kselftests (with timeout disabled, see https://lore.kernel.org/live-patching/20191025115041.23186-1-mbenes@xxxxxxx/) and tests from https://github.com/lpechacek/qa_test_klp. Changes since v1 and questions follow: - rebased on top of v5.4-rc5. It also meant rebasing on top of ARCH_STACKWALK, which made the outcome nicer and addressed some of Joe's remarks. - sp alignment is checked in both _start and _next_frame cases - ftrace_graph_ret_addr() calling cleanup - I tried to use the existing infrastructure as much as possible with one exception. I kept unwind_next_frame_reliable() next to the ordinary unwind_next_frame(). I did not come up with a nice solution how to integrate it. The reliable unwinding is executed on a task stack only, which leads to a nice simplification. My integration attempts only obfuscated the existing unwind_next_frame() which is already not easy to read. Ideas are definitely welcome. - although not nice (Josh mentioned it in his review), I kept checking for kretprobe_trampoline in the main loop. It could go into _start and _next_frame callbacks, but more changes would be required (changing a function return type, ordinary unwinding does not need it). So I did not think it was worth it. I could change it in v3, of course. Miroslav Benes (3): s390/unwind: drop unnecessary code around calling ftrace_graph_ret_addr() s390/unwind: prepare the unwinding interface for reliable stack traces s390/livepatch: Implement reliable stack tracing for the consistency model arch/s390/Kconfig | 1 + arch/s390/include/asm/stacktrace.h | 3 +- arch/s390/include/asm/unwind.h | 15 +++--- arch/s390/kernel/dumpstack.c | 16 +++++- arch/s390/kernel/perf_event.c | 2 +- arch/s390/kernel/stacktrace.c | 48 +++++++++++++++++- arch/s390/kernel/unwind_bc.c | 79 ++++++++++++++++++++++++------ arch/s390/oprofile/init.c | 2 +- 8 files changed, 139 insertions(+), 27 deletions(-) -- 2.23.0
