s390/kasan: avoid report in get_wchan

Reading other running task's stack can be a dangerous endeavor. Kasan
stack memory access instrumentation includes special prologue and epilogue
to mark/remove red zones in shadow memory between stack variables. For
that reason there is always a race between a task reading value in other
task's stack and that other task returning from a function and entering
another one generating different red zones pattern.

To avoid kasan reports simply perform uninstrumented memory reads.

Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 9f2727bf3cbe..b0afec673f77 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -196,12 +196,12 @@ unsigned long get_wchan(struct task_struct *p)
                 goto out;
         }
         for (count = 0; count < 16; count++) {
-                sf = (struct stack_frame *) sf->back_chain;
+                sf = (struct stack_frame *)READ_ONCE_NOCHECK(sf->back_chain);
                 if (sf <= low || sf > high) {
                         return_address = 0;
                         goto out;
                 }
-                return_address = sf->gprs[8];
+                return_address = READ_ONCE_NOCHECK(sf->gprs[8]);
                 if (!in_sched_functions(return_address))
                         goto out;
         }