On Wed, May 17, 2023 at 02:37:41PM -0400, Peter Xu wrote: > On Wed, May 17, 2023 at 06:20:55PM +0100, Lorenzo Stoakes wrote: > > On Wed, May 17, 2023 at 11:04:07AM -0400, Peter Xu wrote: > > > It seems vma merging with uffd paths is broken with either > > > register/unregister, where right now we can feed wrong parameters to > > > vma_merge() and it's found by recent patch which moved asserts upwards in > > > vma_merge() by Lorenzo Stoakes: > > > > > > https://lore.kernel.org/all/ZFunF7DmMdK05MoF@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > > > > > The problem is in the current code base we didn't fixup "prev" for the case > > > where "start" address can be within the "prev" vma section. In that case > > > we should have "prev" points to the current vma rather than the previous > > > one when feeding to vma_merge(). > > > > This doesn't seem quite correct, perhaps - "where start is contained within vma > > but not clamped to its start. We need to convert this into case 4 which permits > > subdivision of prev by assigning vma to prev. As we loop, each subsequent VMA > > will be clamped to the start." > > I think it covers more than case 4 - it can also be case 0 where no merge > will happen? Ugh please let's not call a case that doesn't merge by a number :P but sure of course it might also not merge. > > > > > > > > > This patch will eliminate the report and make sure vma_merge() calls will > > > become legal again. > > > > > > One thing to mention is that the "Fixes: 29417d292bd0" below is there only > > > to help explain where the warning can start to trigger, the real commit to > > > fix should be 69dbe6daf104. Commit 29417d292bd0 helps us to identify the > > > issue, but unfortunately we may want to keep it in Fixes too just to ease > > > kernel backporters for easier tracking. > > > > > > Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx> > > > Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> > > > Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> > > > Reported-by: Mark Rutland <mark.rutland@xxxxxxx> > > > Fixes: 29417d292bd0 ("mm/mmap/vma_merge: always check invariants") > > > Fixes: 69dbe6daf104 ("userfaultfd: use maple tree iterator to iterate VMAs") > > > Closes: https://lore.kernel.org/all/ZFunF7DmMdK05MoF@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > > Cc: linux-stable <stable@xxxxxxxxxxxxxxx> > > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> > > > --- > > > fs/userfaultfd.c | 5 +++++ > > > 1 file changed, 5 insertions(+) > > > > > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > > > index 0fd96d6e39ce..17c8c345dac4 100644 > > > --- a/fs/userfaultfd.c > > > +++ b/fs/userfaultfd.c > > > @@ -1459,6 +1459,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, > > > > > > vma_iter_set(&vmi, start); > > > prev = vma_prev(&vmi); > > > + if (vma->vm_start < start) > > > + prev = vma; > > > > > > ret = 0; > > > for_each_vma_range(vmi, vma, end) { > > > @@ -1625,6 +1627,9 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, > > > > > > vma_iter_set(&vmi, start); > > > prev = vma_prev(&vmi); > > > + if (vma->vm_start < start) > > > + prev = vma; > > > + > > > ret = 0; > > > for_each_vma_range(vmi, vma, end) { > > > cond_resched(); > > > -- > > > 2.39.1 > > > > > > > Other than that looks good:- > > > > Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx> > > Thanks to both on the quick reviews! No problem! > > -- > Peter Xu >
