Implement the core HWBP management for kstackwatch with
pre-allocation strategy to enable atomic context operation.
This patch introduces the fundamental breakthrough that allows kstackwatch
to work in atomic contexts: pre-allocating hardware breakpoints across
all CPUs during initialization, then using arch_reinstall_hw_breakpoint()
to atomically update breakpoint targets without allocation overhead.
Key features:
- Pre-allocate per-CPU hardware breakpoints using register_wide_hw_breakpoint()
- Initialize with a dummy marker address that will be dynamically updated
- Comprehensive corruption detection handler with register dumps and
optional panic trigger
- Clean resource management on module exit
The pre-allocation approach is critical because:
1. Hardware breakpoint allocation can fail or sleep in atomic contexts
2. kprobes run in atomic context where allocation is not permitted
3. Pre-allocated breakpoints can be instantly retargeted using
arch_reinstall_hw_breakpoint() without any blocking operations
This foundation enables the subsequent kprobe integration to atomically
arm/disarm breakpoints on function entry/exit, providing real-time
stack corruption detection without the limitations of traditional
allocation-based approaches.
Signed-off-by: Jinchao Wang <wangjinchao...@gmail.com>
---
mm/kstackwatch/kstackwatch.h | 6 ++++
mm/kstackwatch/watch.c | 65 ++++++++++++++++++++++++++++++++++++
2 files changed, 71 insertions(+)
diff --git a/mm/kstackwatch/kstackwatch.h b/mm/kstackwatch/kstackwatch.h
index f58af36e64a7..256574cd9cb2 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 e69de29bb2d1..5cc2dfef140b 100644
--- a/mm/kstackwatch/watch.c
+++ b/mm/kstackwatch/watch.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kprobes.h>
+#include <linux/hw_breakpoint.h>
+#include <linux/perf_event.h>
+#include <linux/sched/debug.h>
+#include <linux/smp.h>
+#include <linux/slab.h>
+#include <asm/hw_breakpoint.h>
+#include <linux/stacktrace.h>
+#include <linux/delay.h>
+
+#include "kstackwatch.h"
+
+struct perf_event *__percpu *watch_events;
+struct ksw_config *watch_config;
+
+static unsigned long long marker;
+
+/* Enhanced breakpoint handler with watch identification */
+static void ksw_watch_handler(struct perf_event *bp,
+ struct perf_sample_data *data,
+ struct pt_regs *regs)
+{
+ pr_emerg("========== KStackWatch: Caught stack corruption =======\n");
+ pr_emerg("KSW: config %s\n", watch_config->config_str);
+ show_regs(regs);
+ pr_emerg("========== KStackWatch End ==========\n");
+ mdelay(100);
+
+ if (panic_on_catch)
+ panic("KSW: Stack corruption detected");
+}
+
+/* Initialize hardware breakpoint */
+int ksw_watch_init(struct ksw_config *config)
+{
+ struct perf_event_attr attr;
+
+ /* Initialize default breakpoint attributes */
+ hw_breakpoint_init(&attr);
+ attr.bp_addr = (unsigned long)▮
+ 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: HWBP initialized\n");
+ return 0;
+}
+
+/* Cleanup hardware breakpoint */
+void ksw_watch_exit(void)
+{
+ unregister_wide_hw_breakpoint(watch_events);
+ watch_events = NULL;
+
+ pr_info("KSW: HWBP cleaned up\n");
+}
--
2.43.0
