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 BC96F10785; Fri, 3 Jul 2026 13:54:48 +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=1783086889; cv=none; b=NphcS5aBPkJOeAApvsRYY70VCxJ/i62aowfYlGJCorcng8cPJ47nifVrMgNcU4orfrz/pcLRVhdLrHwSYX2gv8sgfqtVHjke+lJhPFOi30RFEGHBsr3Mm7d98Vl60Ypye5aknweDlFsK3VsCVwvSbMWS7u5qx1feqJpUxRFllk4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783086889; c=relaxed/simple; bh=/CtZ3Exkjc6idb1NSE6jDuYoj19Za6xd4nFYiO/AITs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=P6Yx+Rx47Q/whrAWFrplkAHlVziK8R1ISx05td02rHKBwVu0ek8ZXCtyr0qvtpIapadzle/A8GvIsNEatiYvDKWHVMyfB5NTI9h/DIkOUHR1ULgKU4gQ8T24n3uMi75u8NSMoNAnh86ELbsuBngIWQU91cmo6C6NKdYWQzF2+48= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Un1KjgIk; 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="Un1KjgIk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A65891F000E9; Fri, 3 Jul 2026 13:54:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783086888; bh=J7lXeUh6QUNy9Z3dsTupqf3hFsqiT1T6e75ZkSXnH6k=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Un1KjgIkbys6cN/Ii43o3pl8ddXkKk6LxBp1QYwYHVqAumvwlkRdXioMPGIN73xeO 0xk4NWKagLR/ZCxwnwzAc9l/4JEU6U6ODbg4IgW3LPAjFRC1bwK9Oo3RkCQIbtqo70 BaiHodMnXNQjWymSuQbrfD/LEMSd+0awXY8eztt5DK3e36nZ01Lq0GYK3ETzo4dRpe O/ogiFKynuZcJMJwJY8qEx/r70lwjCf7kVWcKreUbYBDIbY2fp2zmMEtxwIEIj7fCs 34e0oGkdAAfjBshDpXVqlbYjplyBtc8Jt0vwD7THDyxyrACXBBSoktmOYJHngsoo6U 1tHF48iLRtTgQ== Date: Fri, 3 Jul 2026 14:54:41 +0100 From: Lorenzo Stoakes To: Mike Rapoport Cc: Andrew Morton , Linus Torvalds , Alexander Viro , Christian Brauner , David Hildenbrand , Jan Kara , Oleg Nesterov , Peter Xu , vova tokarev , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Subject: Re: [PATCH v2] userfaultfd: prevent registration of special VMAs Message-ID: References: <20260618095017.2553004-1-rppt@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: <20260618095017.2553004-1-rppt@kernel.org> On Thu, Jun 18, 2026 at 12:50:17PM +0300, 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_SPECIAL so that if a driver would implement > vm_uffd_ops, it wouldn't be possible to register special VMAs with > userfaultfd. > > Since VM_SPECIAL includes VM_DONTEXPAND which is set but hugetlb, > exclude hugetlb VMAs from the check for VM_SPECIAL. > > Reported-by: vova tokarev > Fixes: 54007f818206 ("mm: Introduce VM_SHADOW_STACK for shadow stack memory") > Cc: > Signed-off-by: Mike Rapoport (Microsoft) LGTM, so: Reviewed-by: Lorenzo Stoakes I'm working on a series to take care of the issues discussed at [0]. [0]:https://lore.kernel.org/all/20260618183442.BBCD71F000E9@smtp.kernel.org > --- > > v2 changes: > * reject all VM_SPECIAL except hugetlb > > v1: https://lore.kernel.org/all/20260617194059.2529406-1-rppt@kernel.org > > mm/userfaultfd.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 246af12bf801..c3adedaaf7d5 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -2111,7 +2111,10 @@ 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_SHADOW_STACK)) > + return false; > + > + if (!is_vm_hugetlb_page(vma) && (vma->vm_flags & VM_SPECIAL)) > return false; > > vm_flags &= __VM_UFFD_FLAGS; > > base-commit: e3d8707358ea76b78bdec9928937bb9a797f2c8f > -- > 2.53.0 > > Cheers, Lorenzo