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

Matthew Wilcox
2020-06-25T17:31:31Z

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.christopherson@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?)