@@ -11,7 +11,20 @@
#include "lkdtm.h"
#include <linux/stackleak.h>
-void lkdtm_STACKLEAK_ERASING(void)
+/*
+ * 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);
@@ -81,3 +94,12 @@ void lkdtm_STACKLEAK_ERASING(void)
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);
+}
The lkdtm_STACKLEAK_ERASING() test is instrumentable and runs with IRQs unmasked, so it's possible for unrelated code to clobber the task stack and/or manipulate current->lowest_stack while the test is running, resulting in spurious failures. The regular stackleak erasing code is non-instrumentable and runs with IRQs masked, preventing similar issues. Make the body of the test non-instrumentable, and run it with IRQs masked, avoiding such spurious failures. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Popov <alex.popov@linux.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Kees Cook <keescook@chromium.org> Cc: Will Deacon <will@kernel.org> --- drivers/misc/lkdtm/stackleak.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-)