1 files changed, 150 insertions, 0 deletions
diff --git a/drivers/misc/lkdtm/stackleak.c b/drivers/misc/lkdtm/stackleak.c
new file mode 100644
index 000000000..f1d022160
--- /dev/null
+++ b/drivers/misc/lkdtm/stackleak.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This code tests that the current task stack is properly erased (filled
+ * with STACKLEAK_POISON).
+ *
+ * Authors:
+ *   Alexander Popov <alex.popov@linux.com>
+ *   Tycho Andersen <tycho@tycho.ws>
+ */
+
+#include "lkdtm.h"
+#include <linux/stackleak.h>
+
+#if defined(CONFIG_GCC_PLUGIN_STACKLEAK)
+/*
+ * Check that stackleak tracks the lowest stack pointer and erases the stack
+ * below this as expected.
+ *
+ * To prevent the lowest stack pointer changing during the test, IRQs are
+ * masked and instrumentation of this function is disabled. We assume that the
+ * compiler will create a fixed-size stack frame for this function.
+ *
+ * Any non-inlined function may make further use of the stack, altering the
+ * lowest stack pointer and/or clobbering poison values. To avoid spurious
+ * failures we must avoid printing until the end of the test or have already
+ * encountered a failure condition.
+ */
+static void noinstr check_stackleak_irqoff(void)
+{
+	const unsigned long task_stack_base = (unsigned long)task_stack_page(current);
+	const unsigned long task_stack_low = stackleak_task_low_bound(current);
+	const unsigned long task_stack_high = stackleak_task_high_bound(current);
+	const unsigned long current_sp = current_stack_pointer;
+	const unsigned long lowest_sp = current->lowest_stack;
+	unsigned long untracked_high;
+	unsigned long poison_high, poison_low;
+	bool test_failed = false;
+
+	/*
+	 * Check that the current and lowest recorded stack pointer values fall
+	 * within the expected task stack boundaries. These tests should never
+	 * fail unless the boundaries are incorrect or we're clobbering the
+	 * STACK_END_MAGIC, and in either casee something is seriously wrong.
+	 */
+	if (current_sp < task_stack_low || current_sp >= task_stack_high) {
+		instrumentation_begin();
+		pr_err("FAIL: current_stack_pointer (0x%lx) outside of task stack bounds [0x%lx..0x%lx]\n",
+		       current_sp, task_stack_low, task_stack_high - 1);
+		test_failed = true;
+		goto out;
+	}
+	if (lowest_sp < task_stack_low || lowest_sp >= task_stack_high) {
+		instrumentation_begin();
+		pr_err("FAIL: current->lowest_stack (0x%lx) outside of task stack bounds [0x%lx..0x%lx]\n",
+		       lowest_sp, task_stack_low, task_stack_high - 1);
+		test_failed = true;
+		goto out;
+	}
+
+	/*
+	 * Depending on what has run prior to this test, the lowest recorded
+	 * stack pointer could be above or below the current stack pointer.
+	 * Start from the lowest of the two.
+	 *
+	 * Poison values are naturally-aligned unsigned longs. As the current
+	 * stack pointer might not be sufficiently aligned, we must align
+	 * downwards to find the lowest known stack pointer value. This is the
+	 * high boundary for a portion of the stack which may have been used
+	 * without being tracked, and has to be scanned for poison.
+	 */
+	untracked_high = min(current_sp, lowest_sp);
+	untracked_high = ALIGN_DOWN(untracked_high, sizeof(unsigned long));
+
+	/*
+	 * Find the top of the poison in the same way as the erasing code.
+	 */
+	poison_high = stackleak_find_top_of_poison(task_stack_low, untracked_high);
+
+	/*
+	 * Check whether the poisoned portion of the stack (if any) consists
+	 * entirely of poison. This verifies the entries that
+	 * stackleak_find_top_of_poison() should have checked.
+	 */
+	poison_low = poison_high;
+	while (poison_low > task_stack_low) {
+		poison_low -= sizeof(unsigned long);
+
+		if (*(unsigned long *)poison_low == STACKLEAK_POISON)
+			continue;
+
+		instrumentation_begin();
+		pr_err("FAIL: non-poison value %lu bytes below poison boundary: 0x%lx\n",
+		       poison_high - poison_low, *(unsigned long *)poison_low);
+		test_failed = true;
+		goto out;
+	}
+
+	instrumentation_begin();
+	pr_info("stackleak stack usage:\n"
+		"  high offset: %lu bytes\n"
+		"  current:     %lu bytes\n"
+		"  lowest:      %lu bytes\n"
+		"  tracked:     %lu bytes\n"
+		"  untracked:   %lu bytes\n"
+		"  poisoned:    %lu bytes\n"
+		"  low offset:  %lu bytes\n",
+		task_stack_base + THREAD_SIZE - task_stack_high,
+		task_stack_high - current_sp,
+		task_stack_high - lowest_sp,
+		task_stack_high - untracked_high,
+		untracked_high - poison_high,
+		poison_high - task_stack_low,
+		task_stack_low - task_stack_base);
+
+out:
+	if (test_failed) {
+		pr_err("FAIL: the thread stack is NOT properly erased!\n");
+	} else {
+		pr_info("OK: the rest of the thread stack is properly erased\n");
+	}
+	instrumentation_end();
+}
+
+static void lkdtm_STACKLEAK_ERASING(void)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	check_stackleak_irqoff();
+	local_irq_restore(flags);
+}
+#else /* defined(CONFIG_GCC_PLUGIN_STACKLEAK) */
+static void lkdtm_STACKLEAK_ERASING(void)
+{
+	if (IS_ENABLED(CONFIG_HAVE_ARCH_STACKLEAK)) {
+		pr_err("XFAIL: stackleak is not enabled (CONFIG_GCC_PLUGIN_STACKLEAK=n)\n");
+	} else {
+		pr_err("XFAIL: stackleak is not supported on this arch (HAVE_ARCH_STACKLEAK=n)\n");
+	}
+}
+#endif /* defined(CONFIG_GCC_PLUGIN_STACKLEAK) */
+
+static struct crashtype crashtypes[] = {
+	CRASHTYPE(STACKLEAK_ERASING),
+};
+
+struct crashtype_category stackleak_crashtypes = {
+	.crashtypes = crashtypes,
+	.len	    = ARRAY_SIZE(crashtypes),
+};