linux-hardening - Re: inconsistence in mprotect_fixup mlock_fixup madvise_update

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Message-ID: <ZIjOlU5EfVNt6NRU@x1n>
Date:   Tue, 13 Jun 2023 16:16:21 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Jeff Xu <jeffxu@...omium.org>
Cc:     linux-mm@...ck.org, linux-hardening@...r.kernel.org,
        Liam.Howlett@...cle.com, zhangpeng.00@...edance.com,
        akpm@...ux-foundation.org, koct9i@...il.com, david@...hat.com,
        ak@...ux.intel.com, hughd@...gle.com, emunson@...mai.com,
        rppt@...ux.ibm.com, aarcange@...hat.com,
        linux-kernel@...r.kernel.org, Lorenzo Stoakes <lstoakes@...il.com>
Subject: Re: inconsistence in mprotect_fixup mlock_fixup madvise_update_vma

Hi, Jeff,

On Tue, Jun 13, 2023 at 08:26:26AM -0700, Jeff Xu wrote:
> + more ppl to the list.
> 
> On Mon, Jun 12, 2023 at 6:04 PM Jeff Xu <jeffxu@...omium.org> wrote:
> >
> > Hello,
> >
> > There seems to be inconsistency in different VMA fixup
> > implementations, for example:
> > mlock_fixup will skip VMA that is hugettlb, etc, but those checks do
> > not exist in mprotect_fixup and madvise_update_vma. Wouldn't this be a
> > problem? the merge/split skipped by mlock_fixup, might get acted on in
> > the madvice/mprotect case.
> >
> > mlock_fixup currently check for
> > if (newflags == oldflags || (oldflags & VM_SPECIAL) ||
> > is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm) ||
> > vma_is_dax(vma) || vma_is_secretmem(vma))

The special handling you mentioned in mlock_fixup mostly makes sense to me.

E.g., I think we can just ignore mlock a hugetlb page if it won't be
swapped anyway.

Do you encounter any issue with above?

> > Should there be a common function to handle VMA merge/split ?

IMHO vma_merge() and split_vma() are the "common functions".  Copy Lorenzo
as I think he has plan to look into the interface to make it even easier to
use.

-- 
Peter Xu