[PATCH v2 04/18] mm/ksw: add HWBP pre-allocation support

Jinchao Wang
2025-09-04T00:22:28Z

Pre-allocate per-CPU hardware breakpoints at init with a dummy address,
which will be retargeted dynamically in kprobe handler. This avoids
allocation in atomic contexts.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
mm/kstackwatch/kstackwatch.h | 6 ++++
mm/kstackwatch/watch.c | 62 ++++++++++++++++++++++++++++++++++++
2 files changed, 68 insertions(+)

diff --git a/mm/kstackwatch/kstackwatch.h b/mm/kstackwatch/kstackwatch.h
index b5f1835586c1..2318779bde70 100644
--- a/mm/kstackwatch/kstackwatch.h
+++ b/mm/kstackwatch/kstackwatch.h
@@ -36,4 +36,10 @@ struct ksw_config {
char config_str[MAX_CONFIG_STR_LEN];
};

+extern bool panic_on_catch;
+
+/* watch management */
+int ksw_watch_init(struct ksw_config *config);
+void ksw_watch_exit(void);
+
#endif /* _KSTACKWATCH_H */
diff --git a/mm/kstackwatch/watch.c b/mm/kstackwatch/watch.c
index cec594032515..e7ed88700b49 100644
--- a/mm/kstackwatch/watch.c
+++ b/mm/kstackwatch/watch.c
@@ -1 +1,63 @@
// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/hw_breakpoint.h>
+#include <linux/kern_levels.h>
+#include <linux/kprobes.h>
+#include <linux/printk.h>
+#include <linux/perf_event.h>
+#include <linux/sched/debug.h>
+#include <linux/slab.h>
+#include <linux/smp.h>
+#include <linux/stacktrace.h>
+
+#include "kstackwatch.h"
+
+#define MAX_STACK_ENTRIES 64
+
+struct perf_event *__percpu *watch_events;
+struct ksw_config *watch_config;
+
+static unsigned long long watch_holder;
+
+static void ksw_watch_handler(struct perf_event *bp,
+ struct perf_sample_data *data,
+ struct pt_regs *regs)
+{
+ pr_err("========== KStackWatch: Caught stack corruption =======\n");
+ pr_err("KSW: config %s\n", watch_config->config_str);
+ show_regs(regs);
+ pr_err("=================== KStackWatch End ==================\n");
+
+ if (panic_on_catch)
+ panic("KSW: Stack corruption detected");
+}
+
+int ksw_watch_init(struct ksw_config *config)
+{
+ struct perf_event_attr attr;
+
+ hw_breakpoint_init(&attr);
+ attr.bp_addr = (unsigned long)&watch_holder;
+ attr.bp_len = HW_BREAKPOINT_LEN_8;
+ attr.bp_type = HW_BREAKPOINT_W;
+ watch_events =
+ register_wide_hw_breakpoint(&attr, ksw_watch_handler, NULL);
+ if (IS_ERR((void *)watch_events)) {
+ int ret = PTR_ERR((void *)watch_events);
+
+ pr_err("KSW: failed to register wide hw breakpoint: %d\n", ret);
+ return ret;
+ }
+
+ watch_config = config;
+ pr_info("KSW: watch inited\n");
+ return 0;
+}
+
+void ksw_watch_exit(void)
+{
+ unregister_wide_hw_breakpoint(watch_events);
+ watch_events = NULL;
+
+ pr_info("KSW: watch exited\n");
+}
--
2.43.0