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KVM: s390: fix locking order problem in enable_sie

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There are potential locking problem in enable_sie. We take the task_lock
and the mmap_sem. As exit_mm uses the same locks vice versa, this triggers
a lockdep warning.
The second problem is that dup_mm and mmput might sleep, so we must not
hold the task_lock at that moment.

The solution is to dup the mm unconditional and use the task_lock before and
afterwards to check  if we can use the new mm. dup_mm and mmput are called
outside the task_lock, but we run update_mm while holding the task_lock,
protection us against ptrace.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Carsten Otte <cotte@de.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Christian Borntraeger 2008-05-21 13:37:29 +02:00 committed by Avi Kivity
parent b8cee18cc7
commit 74b6b522ec
1 changed files with 27 additions and 17 deletions
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44
arch/s390/mm/pgtable.c
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@ -254,36 +254,46 @@ void disable_noexec(struct mm_struct *mm, struct task_struct *tsk)
int s390_enable_sie(void)
{
struct task_struct *tsk = current;
struct mm_struct *mm;
int rc;
struct mm_struct *mm, *old_mm;
task_lock(tsk);
rc = 0;
/* Do we have pgstes? if yes, we are done */
if (tsk->mm->context.pgstes)
goto unlock;
return 0;
rc = -EINVAL;
/* lets check if we are allowed to replace the mm */
task_lock(tsk);
if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||
tsk->mm != tsk->active_mm || tsk->mm->ioctx_list)
goto unlock;
tsk->mm != tsk->active_mm || tsk->mm->ioctx_list) {
task_unlock(tsk);
return -EINVAL;
}
task_unlock(tsk);
tsk->mm->context.pgstes = 1; /* dirty little tricks .. */
/* we copy the mm with pgstes enabled */
tsk->mm->context.pgstes = 1;
mm = dup_mm(tsk);
tsk->mm->context.pgstes = 0;
rc = -ENOMEM;
if (!mm)
goto unlock;
mmput(tsk->mm);
return -ENOMEM;
/* Now lets check again if somebody attached ptrace etc */
task_lock(tsk);
if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||
tsk->mm != tsk->active_mm || tsk->mm->ioctx_list) {
mmput(mm);
task_unlock(tsk);
return -EINVAL;
}
/* ok, we are alone. No ptrace, no threads, etc. */
old_mm = tsk->mm;
tsk->mm = tsk->active_mm = mm;
preempt_disable();
update_mm(mm, tsk);
cpu_set(smp_processor_id(), mm->cpu_vm_mask);
preempt_enable();
rc = 0;
unlock:
task_unlock(tsk);
return rc;
mmput(old_mm);
return 0;
}
EXPORT_SYMBOL_GPL(s390_enable_sie);