| Message ID | 20221116102659.70287-6-david@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | mm/gup: remove FOLL_FORCE usage from drivers (reliable R/O long-term pinning) | expand |
On 11/16/22 11:26, David Hildenbrand wrote: > Let's catch abuse of FAULT_FLAG_WRITE early, such that we don't have to > care in all other handlers and might get "surprises" if we forget to do > so. > > Write faults without VM_MAYWRITE don't make any sense, and our > maybe_mkwrite() logic could have hidden such abuse for now. > > Write faults without VM_WRITE on something that is not a COW mapping is > similarly broken, and e.g., do_wp_page() could end up placing an > anonymous page into a shared mapping, which would be bad. > > This is a preparation for reliable R/O long-term pinning of pages in > private mappings, whereby we want to make sure that we will never break > COW in a read-only private mapping. > > Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> > --- > mm/memory.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/mm/memory.c b/mm/memory.c > index e014435a87db..c4fa378ec2a0 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5170,6 +5170,14 @@ static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma, > */ > if (!is_cow_mapping(vma->vm_flags)) > *flags &= ~FAULT_FLAG_UNSHARE; > + } else if (*flags & FAULT_FLAG_WRITE) { > + /* Write faults on read-only mappings are impossible ... */ > + if (WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE))) > + return VM_FAULT_SIGSEGV; > + /* ... and FOLL_FORCE only applies to COW mappings. */ > + if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE) && > + !is_cow_mapping(vma->vm_flags))) > + return VM_FAULT_SIGSEGV; > } > return 0; > }
diff --git a/mm/memory.c b/mm/memory.c index e014435a87db..c4fa378ec2a0 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5170,6 +5170,14 @@ static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma, */ if (!is_cow_mapping(vma->vm_flags)) *flags &= ~FAULT_FLAG_UNSHARE; + } else if (*flags & FAULT_FLAG_WRITE) { + /* Write faults on read-only mappings are impossible ... */ + if (WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE))) + return VM_FAULT_SIGSEGV; + /* ... and FOLL_FORCE only applies to COW mappings. */ + if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE) && + !is_cow_mapping(vma->vm_flags))) + return VM_FAULT_SIGSEGV; } return 0; }
Let's catch abuse of FAULT_FLAG_WRITE early, such that we don't have to care in all other handlers and might get "surprises" if we forget to do so. Write faults without VM_MAYWRITE don't make any sense, and our maybe_mkwrite() logic could have hidden such abuse for now. Write faults without VM_WRITE on something that is not a COW mapping is similarly broken, and e.g., do_wp_page() could end up placing an anonymous page into a shared mapping, which would be bad. This is a preparation for reliable R/O long-term pinning of pages in private mappings, whereby we want to make sure that we will never break COW in a read-only private mapping. Signed-off-by: David Hildenbrand <david@redhat.com> --- mm/memory.c | 8 ++++++++ 1 file changed, 8 insertions(+)