From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 706863B19AC; Thu, 18 Jun 2026 08:34:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781771654; cv=none; b=WhTEXLifHoJ/7RsEZl304CX0ydt3ITab3E46JVtgbS2VWIaodbd8ZI/Qm2Ks11fpNamZJbSvwiAZD+FCqSQnwbCcHRrYl4nOW75aMAWK1m/jInFg+oeCiUqJRqmpHoOHmW7KmlJYsg/zSA1vs+E5eZN1R6r40R1nnSVred0KRjY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781771654; c=relaxed/simple; bh=jezyeuQMv93oGNybyWc8x5xshbJ7G+UGosXMEBGPnNA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=LkM9KFyEOPBlRsNLRLCnvluvkSEQcD0EVS3tkzode10d9Oy10KBBJTS2wqagYsA9hDZlITVkDFoXAYaAwfMVA8UHPPA2EKFW1GdQsWwHxo651tk31M4MV5nQQq59iRWxf6EUJWXwY72JNepl0zm1QDP8+zonbe70rVKbFWGiAl8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YM57K2za; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="YM57K2za" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D96471F000E9; Thu, 18 Jun 2026 08:34:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781771651; bh=SB6+ZWqOYOVD8J6Bm8SL4mIshI5oOydkw8DYdXdWOWI=; h=Date:From:To:Cc:Subject:References:In-Reply-To; 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5a993689-f730-406d-8515-8bb6025cc851@kernel.org> 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.