This patch series introduces KStackWatch, a lightweight debugging tool to detect kernel stack corruption in real time. It installs a hardware breakpoint (watchpoint) at a function's specified offset using `kprobe.post_handler` and removes it in `fprobe.exit_handler`. This covers the full execution window and reports corruption immediately with time, location, and a call stack.
The motivation comes from scenarios where corruption occurs silently in one function but manifests later in another, without a direct call trace linking the two. Such bugs are often extremely hard to debug with existing tools. These scenarios are demonstrated in test 3–5 (silent corruption test, patch 20). Key features include: * Immediate and precise corruption detection * Support multiple watchpoints for concurrently called functions * Lockless design, usable in any context * Depth filter for recursive calls * Minimal impact on reproducibility * Flexible procfs configuration with key=val syntax To validate the approach, the patch includes a test module and a test script. There is a workflow example described in detail in the documentation (patch 22). Please read the document first if you want an overview. --- Patches 1–3 of this series are also used in the wprobe work proposed by Masami Hiramatsu, so there may be some overlap between our patches. Patch 3 comes directly from Masami Hiramatsu (thanks). --- Changelog V5: * Support key=value input format * Support multiple watchpoints * Support watching instruction inside loop * Support recursion depth tracking with generation * Ignore triggers from fprobe trampoline * Split watch_on into watch_get and watch_on to fail fast * Handle ksw_stack_prepare_watch error * Rewrite silent corruption test * Add multiple watchpoints test * Add an example in documentation V4: https://lore.kernel.org/all/20250912101145.465708-1-wangjinchao...@gmail.com/ * Solve the lockdep issues with: * per-task KStackWatch context to track depth * atomic flag to protect watched_addr * Use refactored version of arch_reinstall_hw_breakpoint V3: https://lore.kernel.org/all/20250910052335.1151048-1-wangjinchao...@gmail.com/ * Use modify_wide_hw_breakpoint_local() (from Masami) * Add atomic flag to restrict /proc/kstackwatch to a single opener * Protect stack probe with an atomic PID flag * Handle CPU hotplug for watchpoints * Add preempt_disable/enable in ksw_watch_on_local_cpu() * Introduce const struct ksw_config *ksw_get_config(void) and use it * Switch to global watch_attr, remove struct watch_info * Validate local_var_len in parser() * Handle case when canary is not found * Use dump_stack() instead of show_regs() to allow module build * Reduce logging and comments * Format logs with KBUILD_MODNAME * Remove unused headers * Add new document V2: https://lore.kernel.org/all/20250904002126.1514566-1-wangjinchao...@gmail.com/ * Make hardware breakpoint and stack operations architecture-independent. V1: https://lore.kernel.org/all/20250828073311.1116593-1-wangjinchao...@gmail.com/ * Replaced kretprobe with fprobe for function exit hooking, as suggested by Masami Hiramatsu * Introduced per-task depth logic to track recursion across scheduling * Removed the use of workqueue for a more efficient corruption check * Reordered patches for better logical flow * Simplified and improved commit messages throughout the series * Removed initial archcheck which should be improved later * Replaced the multiple-thread test with silent corruption test * Split self-tests into a separate patch to improve clarity. * Added a new entry for KStackWatch to the MAINTAINERS file. RFC: https://lore.kernel.org/lkml/20250818122720.434981-1-wangjinchao...@gmail.com/ --- The series is structured as follows: Jinchao Wang (22): x86/hw_breakpoint: Unify breakpoint install/uninstall x86/hw_breakpoint: Add arch_reinstall_hw_breakpoint mm/ksw: add build system support mm/ksw: add ksw_config struct and parser mm/ksw: add singleton /proc/kstackwatch interface mm/ksw: add HWBP pre-allocation mm/ksw: Add atomic watchpoint management api mm/ksw: ignore false positives from exit trampolines mm/ksw: support CPU hotplug sched: add per-task context mm/ksw: add entry kprobe and exit fprobe management mm/ksw: add per-task ctx tracking mm/ksw: resolve stack watch addr and len mm/ksw: manage probe and HWBP lifecycle via procfs mm/ksw: add self-debug helpers mm/ksw: add test module mm/ksw: add stack overflow test mm/ksw: add recursive depth test mm/ksw: add multi-thread corruption test cases tools/ksw: add test script docs: add KStackWatch document MAINTAINERS: add entry for KStackWatch Masami Hiramatsu (Google) (1): HWBP: Add modify_wide_hw_breakpoint_local() API Documentation/dev-tools/index.rst | 1 + Documentation/dev-tools/kstackwatch.rst | 316 ++++++++++++++++++++++ MAINTAINERS | 8 + arch/Kconfig | 10 + arch/x86/Kconfig | 1 + arch/x86/include/asm/hw_breakpoint.h | 8 + arch/x86/kernel/hw_breakpoint.c | 148 ++++++----- include/linux/hw_breakpoint.h | 6 + include/linux/kstackwatch_types.h | 14 + include/linux/sched.h | 5 + kernel/events/hw_breakpoint.c | 37 +++ mm/Kconfig.debug | 18 ++ mm/Makefile | 1 + mm/kstackwatch/Makefile | 8 + mm/kstackwatch/kernel.c | 263 +++++++++++++++++++ mm/kstackwatch/kstackwatch.h | 58 +++++ mm/kstackwatch/stack.c | 240 +++++++++++++++++ mm/kstackwatch/test.c | 332 ++++++++++++++++++++++++ mm/kstackwatch/watch.c | 305 ++++++++++++++++++++++ tools/kstackwatch/kstackwatch_test.sh | 52 ++++ 20 files changed, 1769 insertions(+), 62 deletions(-) create mode 100644 Documentation/dev-tools/kstackwatch.rst create mode 100644 include/linux/kstackwatch_types.h create mode 100644 mm/kstackwatch/Makefile create mode 100644 mm/kstackwatch/kernel.c create mode 100644 mm/kstackwatch/kstackwatch.h create mode 100644 mm/kstackwatch/stack.c create mode 100644 mm/kstackwatch/test.c create mode 100644 mm/kstackwatch/watch.c create mode 100755 tools/kstackwatch/kstackwatch_test.sh -- 2.43.0
