The patch below does not apply to the 3.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From d6e646ad7cfa7034d280459b2b2546288f247144 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Date: Mon, 11 Sep 2017 11:24:22 +0200
Subject: [PATCH] s390/runtime instrumention: fix possible memory corruption
For PREEMPT enabled kernels the runtime instrumentation (RI) code
contains a possible use-after-free bug. If a task that makes use of RI
exits, it will execute do_exit() while still enabled for preemption.
That function will call exit_thread_runtime_instr() via
exit_thread(). If exit_thread_runtime_instr() gets preempted after the
RI control block of the task has been freed but before the pointer to
it is set to NULL, then save_ri_cb(), called from switch_to(), will
write to already freed memory.
Avoid this and simply disable preemption while freeing the control
block and setting the pointer to NULL.
Fixes: e4b8b3f33fca ("s390: add support for runtime instrumentation")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.7+
Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
diff --git a/arch/s390/kernel/runtime_instr.c b/arch/s390/kernel/runtime_instr.c
index 429d3a782f1c..b9738ae2e1de 100644
--- a/arch/s390/kernel/runtime_instr.c
+++ b/arch/s390/kernel/runtime_instr.c
@@ -49,11 +49,13 @@ void exit_thread_runtime_instr(void)
{
struct task_struct *task = current;
+ preempt_disable();
if (!task->thread.ri_cb)
return;
disable_runtime_instr();
kfree(task->thread.ri_cb);
task->thread.ri_cb = NULL;
+ preempt_enable();
}
SYSCALL_DEFINE1(s390_runtime_instr, int, command)
@@ -64,9 +66,7 @@ SYSCALL_DEFINE1(s390_runtime_instr, int, command)
return -EOPNOTSUPP;
if (command == S390_RUNTIME_INSTR_STOP) {
- preempt_disable();
exit_thread_runtime_instr();
- preempt_enable();
return 0;
}