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 A71A43DB629; Thu, 18 Jun 2026 09:35:12 +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=1781775314; cv=none; b=tNgLPX9ua/0ztgBJFnjO7VabpMan07EgyngbiVMDETLanfUhd56mGUvMKLouZHOqhnFgdxe5k9xLnDwD9DBngB7DIFYpGVfwd8A01xz2n/HDskLTKLluap2sgWlvUoM0N2tr3lAK8p6m0BsjzdCmLQYx7Pz+cGSys5zm8bFSPNA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781775314; c=relaxed/simple; bh=zJ7sNs1B62D4n270G/YGpBK00wf5ZQUjvww5dvPiLUM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FDlteH/IyW++JyXX4QZ5I8u0GTHS8DCpwfm4B9UNfJ69rlUsW3vY6mAB3opMAMg4ek1S5owNpmz5MmYY7DCK0ukSCKD796iq0lPY2nMkbwO7wHOMhNk/3rodka6McYF/vYeQM+XT71JwM0mgvcioRQj9QrCjBIPnY+kJC9avO00= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cJVdV6Se; 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="cJVdV6Se" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EDA151F000E9; Thu, 18 Jun 2026 09:35:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781775312; bh=svnJRlqC7nBj8+wumxi3S0D0nQwN9ygt9ENMd/YHoEc=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=cJVdV6SelfsuOc/iIjycuLFBI9QO16gDia1DU906oY9Ep28XwzavtBGwP1CKqO1tm X/upK8GZWfXwOPQUNWjgYujhlCU/dKGy/emkNdqHKJ0XMZ7PaXR8sJYNhXj9hqI9D/ ZyME1MMPXDUgQ8NnAOe03iLKG9Cg+zhJI10/3snoUD1RmCI9lTpG5pnGS0aoxchhMa IcyGmH8Y+MAoYLste+BY/2DzAg9b/lcDp9hdeiGXuJzGG7MwKqT6aoQcIl8VtBUKkE IxY3sKC+z9AJbANQ4BbLx+Jwf24TU9dGs5cKEe3C3t7IVI88dzcgT4YAnu8JbX48AK PBGH1kAftespA== Date: Thu, 18 Jun 2026 12:35:04 +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> <41ef0dce-e973-4947-b5e3-150fdb07f1a6@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: On Thu, Jun 18, 2026 at 11:25:31AM +0200, David Hildenbrand (Arm) wrote: > On 6/18/26 11:21, Mike Rapoport wrote: > > On Thu, Jun 18, 2026 at 10:47:19AM +0200, David Hildenbrand (Arm) wrote: > >> On 6/18/26 10:43, Mike Rapoport wrote: > >>> > >>> Ah, hugetlb sets VM_DONTEXPAND, so it must me excluded to allow uffd with > >>> hugetlb. > >> > >> It would probably be cleaner to just allow hugetlb, and then check for > >> VM_SPECIAL if not hugetlb. > > > > Cleaner in what sense? > > Will be uglier for sure, just take a look at vma_can_userfault(). > > I was thinking of this: > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 180bad42fc79..8a6803618a91 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -2029,7 +2029,10 @@ 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_SHADOW_STACK)) > + return false; > + > + if (!is_vm_hugetlb_page(vma) && (vma->vm_flags & VM_SPECIAL)) > return false; In a way that's an extra check for hugetlb, but it will work. Will respin. > vm_flags &= __VM_UFFD_FLAGS; > > -- > Cheers, > David -- Sincerely yours, Mike.