On Mon, Oct 17, 2022 at 11:06:30AM +0200, Johannes Berg wrote: > From: Johannes Berg <johannes.b...@intel.com> > > Looks like this is needed now, otherwise we get RCU > splats from lockdep. But I don't know anything about > this code ...
You're getting lockdep splats now because there was no checking before. I assumed that the locking was correct before when making this change, and lockdep shows it wasn't ;-) So, you were traversing the list of VMAs with no protection against modification (ie a simulataneous call to mmap()/munmap() would lead to a UAF). I imagine you really want a call to mmap_read_lock() / mmap_read_unlock(), and you'll want to backport it as far as you care about. Maybe this RCU locking is good enough; it'll let you walk the VMAs without any locking, but you have to know that (a) fix_range() doesn't sleep and (b) that if new VMAs are added during the walk or old ones are removed, it doesn't matter whether fix_range() is called on them or not. >From the tone of the email, I infer that you probably haven't done that depth of analysis ;-) Taking the mmap_lock for read is the safe route. > Signed-off-by: Johannes Berg <johannes.b...@intel.com> > --- > arch/um/kernel/tlb.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c > index ad449173a1a1..3cc6b753e579 100644 > --- a/arch/um/kernel/tlb.c > +++ b/arch/um/kernel/tlb.c > @@ -587,8 +587,10 @@ void flush_tlb_mm(struct mm_struct *mm) > struct vm_area_struct *vma; > VMA_ITERATOR(vmi, mm, 0); > > + rcu_read_lock(); > for_each_vma(vmi, vma) > fix_range(mm, vma->vm_start, vma->vm_end, 0); > + rcu_read_unlock(); > } > > void force_flush_all(void) > @@ -597,6 +599,8 @@ void force_flush_all(void) > struct vm_area_struct *vma; > VMA_ITERATOR(vmi, mm, 0); > > + rcu_read_lock(); > for_each_vma(vmi, vma) > fix_range(mm, vma->vm_start, vma->vm_end, 1); > + rcu_read_unlock(); > } > -- > 2.37.3 > _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um
