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b=UR41z7fPG6eVHeAWjFEh8fwBtmodmDzk+F3Lk7VGgBEcVCo7xuYoZlzv7ajxbUgqL 8NHszgXK/0ld2fcayuwb183RFUP1LmOuiz8CbdQgQ+g0aO0woiBL8P+QQK+hbRFoDO scrCxeHw9o6SozJBMF197xUAr85od+/VUepcFepPuO7ob6AsDpPB7baAHXFqQU9bze tLh/Di3w+K881gfrWsflutns/P2W3oo92/VVrZ4xA6cB4Z+qMlmLgc5MtZAvTm2jQo anD2gB94b5c2C0p9yp04vf7bSzD4EtsceR/sSm0clC8omBqYDROVEDgjC8FNutME9t 0mcXH1jXo+WWA== Date: Thu, 18 Jun 2026 11:43:44 +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: X-Rspamd-Queue-Id: 15C6A180002 X-Stat-Signature: 5h3m6bxiokg3fxzss8jb1ddx14saz5xu X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1781772231-716361 X-HE-Meta: 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 jbc1ObEH BPBygqvcvsJKy5HYufz6Hc7I+gUxzaaVKlxsJ5KhiHcT8Nw//RJtr2q+Bt1qQqcktTHBTnWtapJc/1t0QaIngA7uzW0gboszuWpMu9YADuNFvMdrQI1RrXbAPqUbJl4Qxzjjw2AQfLLJvxd+C5umQ4P0e1cUF3IpyozZso/9W2Myz+Og4SgQav2FdRSlNrH5TofoOIOarLCEDHk33TwUfX05J2BMuhzxw4XheDzDsczLPeHx2YwSuloB8XzRB+c+jmX8GHskoKMVa63T4hHF7T5hQcTh/xeGKWF94Hoi/HtCylNM= 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 11:34:12AM +0300, Mike Rapoport wrote: > 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. Ah, hugetlb sets VM_DONTEXPAND, so it must me excluded to allow uffd with hugetlb. -- Sincerely yours, Mike.