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s390/runtime instrumention: fix possible memory corruption

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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>
This commit is contained in:
Heiko Carstens 2017-09-11 11:24:22 +02:00 committed by Martin Schwidefsky
parent 8076428f0c
commit d6e646ad7c
1 changed files with 2 additions and 2 deletions
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4
arch/s390/kernel/runtime_instr.c
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@ -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;
}