[PATCH v4 17/21] mm/ksw: add silent corruption test case

Jinchao Wang
2025-09-12T10:13:24Z

Introduce a new test scenario to simulate silent stack corruption:

- silent_corruption_buggy():
exposes a local variable address globally without resetting it.
- silent_corruption_unwitting():
reads the exposed pointer and modifies the memory, simulating a routine
that unknowingly writes to another stack frame.
- silent_corruption_victim():
demonstrates the effect of silent corruption on unrelated local variables.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
mm/kstackwatch/test.c | 96 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 95 insertions(+), 1 deletion(-)

diff --git a/mm/kstackwatch/test.c b/mm/kstackwatch/test.c
index ab1a3f92b5e8..2b196f72ffd7 100644
--- a/mm/kstackwatch/test.c
+++ b/mm/kstackwatch/test.c
@@ -20,6 +20,9 @@ static struct proc_dir_entry *test_proc;
#define BUFFER_SIZE 4
#define MAX_DEPTH 6

+/* global variables for Silent corruption test */
+static u64 *g_corrupt_ptr;
+
/*
* Test Case 0: Write to the canary position directly (Canary Test)
* use a u64 buffer array to ensure the canary will be placed
@@ -61,6 +64,92 @@ static void canary_test_overflow(void)
pr_info("canary overflow test completed\n");
}

+static void do_something(int min_ms, int max_ms)
+{
+ u32 rand;
+
+ get_random_bytes(&rand, sizeof(rand));
+ rand = min_ms + rand % (max_ms - min_ms + 1);
+ msleep(rand);
+}
+
+static void silent_corruption_buggy(int i)
+{
+ u64 local_var;
+
+ pr_info("starting %s\n", __func__);
+
+ pr_info("%s %d local_var addr: 0x%lx\n", __func__, i,
+ (unsigned long)&local_var);
+ WRITE_ONCE(g_corrupt_ptr, &local_var);
+
+ do_something(50, 150);
+ //buggy: return without resetting g_corrupt_ptr
+}
+
+static void silent_corruption_victim(int i)
+{
+ u64 local_var;
+
+ local_var = 0xdeadbeef;
+ pr_info("starting %s %dth\n", __func__, i);
+ pr_info("%s local_var addr: 0x%lx\n", __func__,
+ (unsigned long)&local_var);
+
+ do_something(50, 150);
+
+ if (local_var != 0)
+ pr_info("%s %d happy with 0x%llx\n", __func__, i, local_var);
+ else
+ pr_info("%s %d unhappy with 0x%llx\n", __func__, i, local_var);
+}
+
+static int silent_corruption_unwitting(void *data)
+{
+ u64 *local_ptr;
+
+ pr_info("starting %s\n", __func__);
+
+ do {
+ local_ptr = READ_ONCE(g_corrupt_ptr);
+ do_something(500, 1000);
+ } while (!local_ptr);
+
+ local_ptr[0] = 0;
+
+ return 0;
+}
+
+/*
+ * Test Case 2: Silent Corruption
+ * buggy() does not protect its local var correctly
+ * unwitting() simply does its intended work
+ * victim() is unaware know what happened
+ */
+static void silent_corruption_test(void)
+{
+ struct task_struct *unwitting;
+
+ pr_info("starting %s\n", __func__);
+ WRITE_ONCE(g_corrupt_ptr, NULL);
+
+ unwitting = kthread_run(silent_corruption_unwitting, NULL, "unwitting");
+ if (IS_ERR(unwitting)) {
+ pr_err("failed to create thread2\n");
+ return;
+ }
+
+ silent_corruption_buggy(0);
+
+ /*
+ * An iteration-based bug: The unwitting thread corrupts the victim's
+ * stack. In a twist of fate, the victim's subsequent repetitions ensure
+ * the corruption is contained, protecting the caller's stack.
+ */
+ for (int i = 0; i < 20; i++)
+ silent_corruption_victim(i);
+}
+
static ssize_t test_proc_write(struct file *file, const char __user *buffer,
size_t count, loff_t *pos)
{
@@ -88,6 +177,10 @@ static ssize_t test_proc_write(struct file *file, const char __user *buffer,
pr_info("triggering canary overflow test\n");
canary_test_overflow();
break;
+ case 2:
+ pr_info("triggering silent corruption test\n");
+ silent_corruption_test();
+ break;
default:
pr_err("Unknown test number %d\n", test_num);
return -EINVAL;
@@ -108,7 +201,8 @@ static ssize_t test_proc_read(struct file *file, char __user *buffer,
"==================================\n"
"Usage:\n"
" echo 'test0' > /proc/kstackwatch_test - Canary write test\n"
- " echo 'test1' > /proc/kstackwatch_test - Canary overflow test\n";
+ " echo 'test1' > /proc/kstackwatch_test - Canary overflow test\n"
+ " echo 'test2' > /proc/kstackwatch_test - Silent corruption test\n";

return simple_read_from_buffer(buffer, count, pos, usage,
strlen(usage));
--
2.43.0