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@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d6e646ad7cfa7034d280459b2b2546288f247144 Mon Sep 17 00:00:00 2001

From: Heiko Carstens heiko.carstens@de.ibm.com 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@vger.kernel.org # v3.7+ Reviewed-by: Christian Borntraeger borntraeger@de.ibm.com Signed-off-by: Heiko Carstens heiko.carstens@de.ibm.com Signed-off-by: Martin Schwidefsky schwidefsky@de.ibm.com

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; }