| Message ID | 20190823221753.2514-3-rcampbell@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/hmm: two bug fixes for hmm_range_fault() | expand |
On Fri, Aug 23, 2019 at 03:17:53PM -0700, Ralph Campbell wrote: > Normally, callers to handle_mm_fault() are supposed to check the > vma->vm_flags first. hmm_range_fault() checks for VM_READ but doesn't > check for VM_WRITE if the caller requests a page to be faulted in > with write permission (via the hmm_range.pfns[] value). > If the vma is write protected, this can result in an infinite loop: > hmm_range_fault() > walk_page_range() > ... > hmm_vma_walk_hole() > hmm_vma_walk_hole_() > hmm_vma_do_fault() > handle_mm_fault(FAULT_FLAG_WRITE) > /* returns VM_FAULT_WRITE */ > /* returns -EBUSY */ > /* returns -EBUSY */ > /* returns -EBUSY */ > /* loops on -EBUSY and range->valid */ > Prevent this by checking for vma->vm_flags & VM_WRITE before calling > handle_mm_fault(). > > Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> Looks good, Reviewed-by: Christoph Hellwig <hch@lst.de>
On Fri, Aug 23, 2019 at 03:17:53PM -0700, Ralph Campbell wrote: > Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> > mm/hmm.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/hmm.c b/mm/hmm.c > index 29371485fe94..4882b83aeccb 100644 > +++ b/mm/hmm.c > @@ -292,6 +292,9 @@ static int hmm_vma_walk_hole_(unsigned long addr, unsigned long end, > hmm_vma_walk->last = addr; > i = (addr - range->start) >> PAGE_SHIFT; > > + if (write_fault && walk->vma && !(walk->vma->vm_flags & VM_WRITE)) > + return -EPERM; Can walk->vma be NULL here? hmm_vma_do_fault() touches it unconditionally. Jason
On 8/27/19 11:41 AM, Jason Gunthorpe wrote: > On Fri, Aug 23, 2019 at 03:17:53PM -0700, Ralph Campbell wrote: > >> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> >> mm/hmm.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/mm/hmm.c b/mm/hmm.c >> index 29371485fe94..4882b83aeccb 100644 >> +++ b/mm/hmm.c >> @@ -292,6 +292,9 @@ static int hmm_vma_walk_hole_(unsigned long addr, unsigned long end, >> hmm_vma_walk->last = addr; >> i = (addr - range->start) >> PAGE_SHIFT; >> >> + if (write_fault && walk->vma && !(walk->vma->vm_flags & VM_WRITE)) >> + return -EPERM; > > Can walk->vma be NULL here? hmm_vma_do_fault() touches it > unconditionally. > > Jason > walk->vma can be NULL. hmm_vma_do_fault() no longer touches it unconditionally, that is what the preceding patch fixes. I suppose I could change hmm_vma_walk_hole_() to check for NULL and fill in the pfns[] array, I just chose to handle it in hmm_vma_do_fault().
On Tue, Aug 27, 2019 at 01:16:13PM -0700, Ralph Campbell wrote: > > On 8/27/19 11:41 AM, Jason Gunthorpe wrote: > > On Fri, Aug 23, 2019 at 03:17:53PM -0700, Ralph Campbell wrote: > > > > > Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> > > > mm/hmm.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/mm/hmm.c b/mm/hmm.c > > > index 29371485fe94..4882b83aeccb 100644 > > > +++ b/mm/hmm.c > > > @@ -292,6 +292,9 @@ static int hmm_vma_walk_hole_(unsigned long addr, unsigned long end, > > > hmm_vma_walk->last = addr; > > > i = (addr - range->start) >> PAGE_SHIFT; > > > + if (write_fault && walk->vma && !(walk->vma->vm_flags & VM_WRITE)) > > > + return -EPERM; > > > > Can walk->vma be NULL here? hmm_vma_do_fault() touches it > > unconditionally. > > > > Jason > > > walk->vma can be NULL. hmm_vma_do_fault() no longer touches it > unconditionally, that is what the preceding patch fixes. > I suppose I could change hmm_vma_walk_hole_() to check for NULL > and fill in the pfns[] array, I just chose to handle it in > hmm_vma_do_fault(). Okay, yes maybe long term it would be clearer to do the vma null check closer to the start of the callback, but this is a good enough bug fix Reviewed-by: Jason Gunthorpe <jgg@mellanox.com> Jason
diff --git a/mm/hmm.c b/mm/hmm.c index 29371485fe94..4882b83aeccb 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -292,6 +292,9 @@ static int hmm_vma_walk_hole_(unsigned long addr, unsigned long end, hmm_vma_walk->last = addr; i = (addr - range->start) >> PAGE_SHIFT; + if (write_fault && walk->vma && !(walk->vma->vm_flags & VM_WRITE)) + return -EPERM; + for (; addr < end; addr += PAGE_SIZE, i++) { pfns[i] = range->values[HMM_PFN_NONE]; if (fault || write_fault) {
Normally, callers to handle_mm_fault() are supposed to check the vma->vm_flags first. hmm_range_fault() checks for VM_READ but doesn't check for VM_WRITE if the caller requests a page to be faulted in with write permission (via the hmm_range.pfns[] value). If the vma is write protected, this can result in an infinite loop: hmm_range_fault() walk_page_range() ... hmm_vma_walk_hole() hmm_vma_walk_hole_() hmm_vma_do_fault() handle_mm_fault(FAULT_FLAG_WRITE) /* returns VM_FAULT_WRITE */ /* returns -EBUSY */ /* returns -EBUSY */ /* returns -EBUSY */ /* loops on -EBUSY and range->valid */ Prevent this by checking for vma->vm_flags & VM_WRITE before calling handle_mm_fault(). Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> --- mm/hmm.c | 3 +++ 1 file changed, 3 insertions(+)