lib: add optional linked list debugging

When enabled, this outputs messages like:

  list_del corruption, 000000005fe4a9d0->next is LIST_POISON1 (0000000000000100)

which can be useful when debugging.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20240103101948.2630473-2-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

3 files changed, 79 insertions, 0 deletions

diff --git a/lib/Kconfig.hardening b/lib/Kconfig.hardening
index f14b256a7d..5c8f0f1a19 100644
--- a/lib/Kconfig.hardening
+++ b/lib/Kconfig.hardening
@@ -1,5 +1,15 @@
 menu "Hardening options"
 
+config BUG_ON_DATA_CORRUPTION
+	bool "Trigger a BUG when data corruption is detected"
+	select DEBUG_LIST
+	help
+	  Select this option if barebox should BUG when it encounters
+	  data corruption in its memory structures when they get checked
+	  for validity.
+
+	  If unsure, say N.
+
 config STACK_GUARD_PAGE
 	bool "Place guard page to catch stack overflows"
 	depends on ARM && MMU
diff --git a/lib/Makefile b/lib/Makefile
index 38204c8273..853d8870fe 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -71,6 +71,7 @@ obj-$(CONFIG_FONTS)	+= fonts/
 obj-$(CONFIG_BAREBOX_LOGO)     += logo/
 obj-y			+= reed_solomon/
 obj-$(CONFIG_RATP)	+= ratp.o
+obj-$(CONFIG_DEBUG_LIST) += list_debug.o
 obj-y			+= list_sort.o
 obj-y			+= refcount.o
 obj-y			+= int_sqrt.o
diff --git a/lib/list_debug.c b/lib/list_debug.c
new file mode 100644
index 0000000000..7de4c709a3
--- /dev/null
+++ b/lib/list_debug.c
@@ -0,0 +1,68 @@
+/*
+ * Copyright 2006, Red Hat, Inc., Dave Jones
+ * Released under the General Public License (GPL).
+ *
+ * This file contains the linked list validation for DEBUG_LIST.
+ */
+
+#include <linux/export.h>
+#include <linux/list.h>
+#include <linux/bug.h>
+#include <linux/kernel.h>
+
+/*
+ * Check that the data structures for the list manipulations are reasonably
+ * valid. Failures here indicate memory corruption (and possibly an exploit
+ * attempt).
+ */
+
+bool __list_add_valid_or_report(struct list_head *new, struct list_head *prev,
+				struct list_head *next)
+{
+	if (CHECK_DATA_CORRUPTION(prev == NULL,
+			"list_add corruption. prev is NULL.\n") ||
+	    CHECK_DATA_CORRUPTION(next == NULL,
+			"list_add corruption. next is NULL.\n") ||
+	    CHECK_DATA_CORRUPTION(next->prev != prev,
+			"list_add corruption. next->prev should be prev (%px), but was %px. (next=%px).\n",
+			prev, next->prev, next) ||
+	    CHECK_DATA_CORRUPTION(prev->next != next,
+			"list_add corruption. prev->next should be next (%px), but was %px. (prev=%px).\n",
+			next, prev->next, prev) ||
+	    CHECK_DATA_CORRUPTION(new == prev || new == next,
+			"list_add double add: new=%px, prev=%px, next=%px.\n",
+			new, prev, next))
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL(__list_add_valid_or_report);
+
+bool __list_del_entry_valid_or_report(struct list_head *entry)
+{
+	struct list_head *prev, *next;
+
+	prev = entry->prev;
+	next = entry->next;
+
+	if (CHECK_DATA_CORRUPTION(next == NULL,
+			"list_del corruption, %px->next is NULL\n", entry) ||
+	    CHECK_DATA_CORRUPTION(prev == NULL,
+			"list_del corruption, %px->prev is NULL\n", entry) ||
+	    CHECK_DATA_CORRUPTION(next == LIST_POISON1,
+			"list_del corruption, %px->next is LIST_POISON1 (%px)\n",
+			entry, LIST_POISON1) ||
+	    CHECK_DATA_CORRUPTION(prev == LIST_POISON2,
+			"list_del corruption, %px->prev is LIST_POISON2 (%px)\n",
+			entry, LIST_POISON2) ||
+	    CHECK_DATA_CORRUPTION(prev->next != entry,
+			"list_del corruption. prev->next should be %px, but was %px. (prev=%px)\n",
+			entry, prev->next, prev) ||
+	    CHECK_DATA_CORRUPTION(next->prev != entry,
+			"list_del corruption. next->prev should be %px, but was %px. (next=%px)\n",
+			entry, next->prev, next))
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL(__list_del_entry_valid_or_report);