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>
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@ -49,11 +49,13 @@ void exit_thread_runtime_instr(void)
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{
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struct task_struct *task = current;
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preempt_disable();
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if (!task->thread.ri_cb)
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return;
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disable_runtime_instr();
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kfree(task->thread.ri_cb);
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task->thread.ri_cb = NULL;
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preempt_enable();
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}
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SYSCALL_DEFINE1(s390_runtime_instr, int, command)
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@ -64,9 +66,7 @@ SYSCALL_DEFINE1(s390_runtime_instr, int, command)
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return -EOPNOTSUPP;
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if (command == S390_RUNTIME_INSTR_STOP) {
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preempt_disable();
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exit_thread_runtime_instr();
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preempt_enable();
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return 0;
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}
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