1 files changed, 99 insertions, 46 deletions

diff --git a/drivers/misc/lkdtm/stackleak.c b/drivers/misc/lkdtm/stackleak.c
index 00db21ff115e..82369c6f889e 100644
--- a/drivers/misc/lkdtm/stackleak.c
+++ b/drivers/misc/lkdtm/stackleak.c
@@ -11,72 +11,125 @@
 #include "lkdtm.h"
 #include <linux/stackleak.h>
 
-void lkdtm_STACKLEAK_ERASING(void)
+#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)
 {
-	unsigned long *sp, left, found, i;
-	const unsigned long check_depth =
-			STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
+	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;
 
 	/*
-	 * For the details about the alignment of the poison values, see
-	 * the comment in stackleak_track_stack().
+	 * 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.
 	 */
-	sp = PTR_ALIGN(&i, sizeof(unsigned long));
-
-	left = ((unsigned long)sp & (THREAD_SIZE - 1)) / sizeof(unsigned long);
-	sp--;
+	if (current_sp < task_stack_low || current_sp >= task_stack_high) {
+		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) {
+		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;
+	}
 
 	/*
-	 * One 'long int' at the bottom of the thread stack is reserved
-	 * and not poisoned.
+	 * 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.
 	 */
-	if (left > 1) {
-		left--;
-	} else {
-		pr_err("FAIL: not enough stack space for the test\n");
-		test_failed = true;
-		goto end;
-	}
+	untracked_high = min(current_sp, lowest_sp);
+	untracked_high = ALIGN_DOWN(untracked_high, sizeof(unsigned long));
 
-	pr_info("checking unused part of the thread stack (%lu bytes)...\n",
-					left * 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);
 
 	/*
-	 * Search for 'check_depth' poison values in a row (just like
-	 * stackleak_erase() does).
+	 * 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.
 	 */
-	for (i = 0, found = 0; i < left && found <= check_depth; i++) {
-		if (*(sp - i) == STACKLEAK_POISON)
-			found++;
-		else
-			found = 0;
-	}
+	poison_low = poison_high;
+	while (poison_low > task_stack_low) {
+		poison_low -= sizeof(unsigned long);
+
+		if (*(unsigned long *)poison_low == STACKLEAK_POISON)
+			continue;
 
-	if (found <= check_depth) {
-		pr_err("FAIL: the erased part is not found (checked %lu bytes)\n",
-						i * sizeof(unsigned long));
+		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 end;
 	}
 
-	pr_info("the erased part begins after %lu not poisoned bytes\n",
-				(i - found) * sizeof(unsigned long));
-
-	/* The rest of thread stack should be erased */
-	for (; i < left; i++) {
-		if (*(sp - i) != STACKLEAK_POISON) {
-			pr_err("FAIL: bad value number %lu in the erased part: 0x%lx\n",
-								i, *(sp - i));
-			test_failed = true;
-		}
-	}
+	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);
 
-end:
+out:
 	if (test_failed) {
 		pr_err("FAIL: the thread stack is NOT properly erased!\n");
-		pr_expected_config(CONFIG_GCC_PLUGIN_STACKLEAK);
 	} else {
 		pr_info("OK: the rest of the thread stack is properly erased\n");
 	}
 }
+
+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) */
+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) */