Re: [PATCH v33 10/21] mm: Introduce vm_ops->may_mprotect()

[Matthew Wilcox]

On Thu, Jun 25, 2020 at 07:14:16PM +0200, Borislav Petkov wrote:
> On Thu, Jun 18, 2020 at 01:08:32AM +0300, Jarkko Sakkinen wrote:
> > From: Sean Christopherson <sean.j.christopher...@intel.com>
> 
> Something ate the Cc:s. Lemme add the mm list, akpm is already on Cc.
> 
> Leaving in the rest for mm folks.

Thanks!

> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index dc7b87310c10..be40b9c29327 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -542,6 +542,8 @@ struct vm_operations_struct {
> >     void (*close)(struct vm_area_struct * area);
> >     int (*split)(struct vm_area_struct * area, unsigned long addr);
> >     int (*mremap)(struct vm_area_struct * area);
> > +   int (*may_mprotect)(struct vm_area_struct *vma, unsigned long start,
> > +                       unsigned long end, unsigned long prot);

This is unlike any other vm operation.  Every other one is a verb.

> > diff --git a/mm/mprotect.c b/mm/mprotect.c
> > index ce8b8a5eacbb..f7731dc13ff0 100644
> > --- a/mm/mprotect.c
> > +++ b/mm/mprotect.c
> > @@ -603,13 +603,21 @@ static int do_mprotect_pkey(unsigned long start, 
> > size_t len,
> >                     goto out;
> >             }
> >  
> > +           tmp = vma->vm_end;
> > +           if (tmp > end)
> > +                   tmp = end;
> > +
> > +           if (vma->vm_ops && vma->vm_ops->may_mprotect) {
> > +                   error = vma->vm_ops->may_mprotect(vma, nstart, tmp,
> > +                                                     prot);
> > +                   if (error)
> > +                           goto out;
> > +           }
> > +
> >             error = security_file_mprotect(vma, reqprot, prot);
> >             if (error)
> >                     goto out;
> >  

I think the right way to do this is:

                error = security_file_mprotect(vma, reqprot, prot);
                if (error)
                        goto out;

                tmp = vma->vm_end;
                if (tmp > end)
                        tmp = end;
+               if (vma->vm_ops->mprotect)
+                       error = vma->vm_ops->mprotect(vma, &prev, nstart, tmp,
+                                       newflags);
+               else
+                       error = mprotect_fixup(vma, &prev, nstart, tmp,
+                                       newflags);
-               error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
                if (error)
                        goto out;

and then the vma owner can do whatever it needs to before calling
mprotect_fixup(), which is already not static.

(how did we get to v33 with this kind of problem still in the patch set?)