releases/4.4.103/s390-runtime-instrumention-fix-possible-memory-corruption.patch

   1 From d6e646ad7cfa7034d280459b2b2546288f247144 Mon Sep 17 00:00:00 2001
   2 From: Heiko Carstens <heiko.carstens@de.ibm.com>
   3 Date: Mon, 11 Sep 2017 11:24:22 +0200
   4 Subject: s390/runtime instrumention: fix possible memory corruption
   5
   6 From: Heiko Carstens <heiko.carstens@de.ibm.com>
   7
   8 commit d6e646ad7cfa7034d280459b2b2546288f247144 upstream.
   9
  10 For PREEMPT enabled kernels the runtime instrumentation (RI) code
  11 contains a possible use-after-free bug. If a task that makes use of RI
  12 exits, it will execute do_exit() while still enabled for preemption.
  13
  14 That function will call exit_thread_runtime_instr() via
  15 exit_thread(). If exit_thread_runtime_instr() gets preempted after the
  16 RI control block of the task has been freed but before the pointer to
  17 it is set to NULL, then save_ri_cb(), called from switch_to(), will
  18 write to already freed memory.
  19
  20 Avoid this and simply disable preemption while freeing the control
  21 block and setting the pointer to NULL.
  22
  23 Fixes: e4b8b3f33fca ("s390: add support for runtime instrumentation")
  24 Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
  25 Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
  26 Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
  27 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  28
  29 ---
  30  arch/s390/kernel/runtime_instr.c |    4 ++--
  31  1 file changed, 2 insertions(+), 2 deletions(-)
  32
  33 --- a/arch/s390/kernel/runtime_instr.c
  34 +++ b/arch/s390/kernel/runtime_instr.c
  35 @@ -47,11 +47,13 @@ void exit_thread_runtime_instr(void)
  36  {
  37         struct task_struct *task = current;
  38
  39 +       preempt_disable();
  40         if (!task->thread.ri_cb)
  41                 return;
  42         disable_runtime_instr();
  43         kfree(task->thread.ri_cb);
  44         task->thread.ri_cb = NULL;
  45 +       preempt_enable();
  46  }
  47
  48  SYSCALL_DEFINE1(s390_runtime_instr, int, command)
  49 @@ -62,9 +64,7 @@ SYSCALL_DEFINE1(s390_runtime_instr, int,
  50                 return -EOPNOTSUPP;
  51
  52         if (command == S390_RUNTIME_INSTR_STOP) {
  53 -               preempt_disable();
  54                 exit_thread_runtime_instr();
  55 -               preempt_enable();
  56                 return 0;
  57         }
  58