[PATCH v2 3/3] lkdtm/bugs: Add CORRUPT_STACK_END to test the scheduler stack end check

[Chris Down <chris@chrisdown.name>]

There's no existing test for the stack end check in schedule(), so add
one.

CORRUPT_STACK_END overwrites the magic at the end of the current task's
stack and then calls schedule(). That should panic when the check is
enabled. When it isn't, the test restores the magic and uses
pr_expected_config_param() to say whether that was expected.

Signed-off-by: Chris Down <chris@chrisdown.name>
---
 drivers/misc/lkdtm/bugs.c               | 21 +++++++++++++++++++++
 tools/testing/selftests/lkdtm/tests.txt |  1 +
 2 files changed, 22 insertions(+)

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index 2761685cf4f8..a39cde7495d3 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -215,6 +215,26 @@ static noinline void lkdtm_CORRUPT_STACK_STRONG(void)
 	__lkdtm_CORRUPT_STACK((void *)&data);
 }
 
+static void lkdtm_CORRUPT_STACK_END(void)
+{
+	unsigned long *stack_end = end_of_stack(current);
+
+	if (READ_ONCE(*stack_end) != STACK_END_MAGIC) {
+		pr_err("FAIL: stack end magic is already corrupted\n");
+		return;
+	}
+
+	pr_info("Corrupting stack end magic and calling schedule() ...\n");
+	WRITE_ONCE(*stack_end, ~STACK_END_MAGIC);
+	schedule_timeout_uninterruptible(1);
+
+	/* Still alive, so let's restore the magic so nothing else trips over it. */
+	WRITE_ONCE(*stack_end, STACK_END_MAGIC);
+	pr_err("FAIL: corrupted stack end was not detected by the scheduler\n");
+	pr_expected_config_param(CONFIG_SCHED_STACK_END_CHECK,
+				 "sched_stack_end_check");
+}
+
 static pid_t stack_pid;
 static unsigned long stack_addr;
 
@@ -885,6 +905,7 @@ static struct crashtype crashtypes[] = {
 	CRASHTYPE(EXHAUST_STACK),
 	CRASHTYPE(CORRUPT_STACK),
 	CRASHTYPE(CORRUPT_STACK_STRONG),
+	CRASHTYPE(CORRUPT_STACK_END),
 	CRASHTYPE(REPORT_STACK),
 	CRASHTYPE(REPORT_STACK_CANARY),
 	CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE),
diff --git a/tools/testing/selftests/lkdtm/tests.txt b/tools/testing/selftests/lkdtm/tests.txt
index bec57a02913a..2d856ed77a64 100644
--- a/tools/testing/selftests/lkdtm/tests.txt
+++ b/tools/testing/selftests/lkdtm/tests.txt
@@ -10,6 +10,7 @@ EXCEPTION
 #EXHAUST_STACK Corrupts memory on failure
 #CORRUPT_STACK Crashes entire system on success
 #CORRUPT_STACK_STRONG Crashes entire system on success
+#CORRUPT_STACK_END Crashes entire system on success
 ARRAY_BOUNDS call trace:|UBSAN: array-index-out-of-bounds
 FAM_BOUNDS call trace:|UBSAN: array-index-out-of-bounds
 PTR_BOUNDS call trace:|UBSAN: array-index-out-of-bounds
-- 
2.56.1