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b=YM57K2za+CC6RytagmjmCqXnGQc+SkdnKMBuOZwnO2NqsfRcfFEpbGzEn72iCkPg7 Adu28iwlNOIklDbu/PZI1NjZFE2MY/VVPalsuFkVouPiL9IY8E7E0rGoOGeHei/Rnp YA0W3poKHIA6DCrOmWDA37W/6mQ6Di08BvfNXJuagpMB9PVY0I2cIR9kKo0trJy20Z 2eHZLmiFXByxMoz2YPVv4mXkjmjCA35cnnAvKV8gxesoW/n2n1njTLodZfUhP9hZ96 uFJm7n0ajHBoYrRdjyJ3qv/dH65lDSVgOM16OoKUwWqjw2BVqsN/vSjy1h8PEK4v0m /I3p8zP71uT4g== Date: Thu, 18 Jun 2026 11:34:05 +0300 From: Mike Rapoport To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Linus Torvalds , Alexander Viro , Christian Brauner , Jan Kara , Oleg Nesterov , Peter Xu , vova tokarev , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Subject: Re: [PATCH] userfaultfd: prevent registration of special VMAs Message-ID: References: <20260617194059.2529406-1-rppt@kernel.org> <5a993689-f730-406d-8515-8bb6025cc851@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5a993689-f730-406d-8515-8bb6025cc851@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D47DE2000D X-Stat-Signature: 1inbgk45xwizcgdyu6hxh68fsyfo5iog X-HE-Tag: 1781771652-677320 X-HE-Meta: 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 54b1/kjm WLUUcfvOSwdWQJmIQtTIue600iiogr6UcNQ/VIdheLTlxTaTkBBq9d7/oitrB/fBFK6abxIBk46Hzz7RyRmYoBAwNEdac5fooBi31T+fwumeM+7qstRNTM0qeMAurmNr4b5SFF+/pzLxy+/+XWIADWslbYMs7tqx6C7sIR4TfZHNEQL0Uucc7m2/f8aiUmbQazPgotoIY1I2NcjPSffdPBh4NLUvnUSPL/G0Arp1jc3/BK9jS+v3V3tOS0gcBkx3QavLLIqoSOZiNHBbVHJ4/bpElWBj0eTUS4UEmrPZySeldkp4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jun 18, 2026 at 10:19:17AM +0200, David Hildenbrand (Arm) wrote: > On 6/17/26 21:40, Mike Rapoport wrote: > > From: "Mike Rapoport (Microsoft)" > > > > Vova Tokarev says: > > > > userfaultfd allows registration on shadow stack VMAs. With userfaultfd > > access, you can register on the shadow stack, discard a page ... and > > inject a page with chosen return addresses via UFFDIO_COPY. > > > > Update vma_can_userfault() to reject VM_SHADOW_STACK. > > > > While on it, also reject VM_IO, VM_MIXEDMAP and VM_PFNMAP so that if a > > driver would implement vm_uffd_ops, it wouldn't be possible to register > > special VMAs with userfaultfd. > > > > Reported-by: vova tokarev > > Fixes: 54007f818206 ("mm: Introduce VM_SHADOW_STACK for shadow stack memory") > > Cc: > > Signed-off-by: Mike Rapoport (Microsoft) > > --- > > mm/userfaultfd.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > > index 246af12bf801..b8d2d87ce8d7 100644 > > --- a/mm/userfaultfd.c > > +++ b/mm/userfaultfd.c > > @@ -2111,7 +2111,8 @@ static bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags, > > { > > const struct vm_uffd_ops *ops = vma_uffd_ops(vma); > > > > - if (vma->vm_flags & VM_DROPPABLE) > > + if (vma->vm_flags & (VM_DROPPABLE | VM_IO | VM_MIXEDMAP | VM_PFNMAP | > > + VM_SHADOW_STACK)) > > I'm sure you considered VM_SPECIAL, which additionally includes VM_DONTEXPAND. > > Would that be better, or what was the reason to allow VM_DONTEXPAND? By itself VM_DONTEXPAND won't matter, as uffd can't resize a VMA. But thinking more about it, it's better to make vma_can_userfault() more restrictive and just use VM_SPECIAL. > -- > Cheers, > > David -- Sincerely yours, Mike.