[PATCH v2] kfence: enable check kfence canary in panic via boot param

[Shaobo Huang]

From: huangshaobo <huangshaobo6@xxxxxxxxxx>

when writing out of bounds to the red zone, it can only be
detected at kfree. However, the system may have been reset
before freeing the memory, which would result in undetected
oob. Therefore, it is necessary to detect oob behavior in
panic. Since only the allocated mem call stack is available,
it may be difficult to find the oob maker. Therefore, this
feature is disabled by default and can only be enabled via
boot parameter.

Suggested-by: chenzefeng <chenzefeng2@xxxxxxxxxx>
Signed-off-by: huangshaobo <huangshaobo6@xxxxxxxxxx>
---
v2:
- it is only detected in panic.
- it is disabled by default.
- can only be enabled via boot parameter.
- the code is moved to the specified partition.
Thanks to Marco for the valuable modification suggestion.
---
 mm/kfence/core.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 9b2b5f56f4ae..0b2b934a1666 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -29,6 +29,8 @@
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/string.h>
+#include <linux/notifier.h>
+#include <linux/panic_notifier.h>
 
 #include <asm/kfence.h>
 
@@ -99,6 +101,10 @@ module_param_named(skip_covered_thresh, kfence_skip_covered_thresh, ulong, 0644)
 static bool kfence_deferrable __read_mostly = IS_ENABLED(CONFIG_KFENCE_DEFERRABLE);
 module_param_named(deferrable, kfence_deferrable, bool, 0444);
 
+/* If true, check kfence canary in panic. */
+static bool kfence_check_on_panic;
+module_param_named(check_on_panic, kfence_check_on_panic, bool, 0444);
+
 /* The pool of pages used for guard pages and objects. */
 char *__kfence_pool __read_mostly;
 EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */
@@ -727,6 +733,30 @@ static int __init kfence_debugfs_init(void)
 
 late_initcall(kfence_debugfs_init);
 
+/* === Panic Notifier ====================================================== */
+static void kfence_check_all_canary(void)
+{
+	int i;
+
+	for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
+		struct kfence_metadata *meta = &kfence_metadata[i];
+
+		if (meta->state == KFENCE_OBJECT_ALLOCATED)
+			for_each_canary(meta, check_canary_byte);
+	}
+}
+
+static int kfence_check_canary_callback(struct notifier_block *nb,
+					unsigned long reason, void *arg)
+{
+	kfence_check_all_canary();
+	return NOTIFY_OK;
+}
+
+static struct notifier_block kfence_check_canary_notifier = {
+	.notifier_call = kfence_check_canary_callback,
+};
+
 /* === Allocation Gate Timer ================================================ */
 
 static struct delayed_work kfence_timer;
@@ -804,6 +834,9 @@ static void kfence_init_enable(void)
 	else
 		INIT_DELAYED_WORK(&kfence_timer, toggle_allocation_gate);
 
+	if (kfence_check_on_panic)
+		atomic_notifier_chain_register(&panic_notifier_list, &kfence_check_canary_notifier);
+
 	WRITE_ONCE(kfence_enabled, true);
 	queue_delayed_work(system_unbound_wq, &kfence_timer, 0);
 
-- 
2.12.3