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

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