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 6B48938654F; Thu, 18 Jun 2026 08:19:22 +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=1781770765; cv=none; b=P7leeajcdAmMilIUDsShg6cjUOzElePHiZ66pEaO5yOGvx/5AFMdm8jfVKDa72V/7NLvPWqFi3Qlr+zBy+UmmTo9d7oRPw8rQ4n6z8KcUEgrLNOOCuLUyED1UBs6aq0TlPCtbsDonjk8yNRdD6pVnmP0sbR17DBXKWVJj3mYkrA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781770765; c=relaxed/simple; bh=rXGd6XbK8o1F3hkDMu2Kr9ZKehK7T0kMEhmAFhYAelQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Z3FyyAQBlFwxapV/J58K/2h2m+FM8L+09BQT57u/Qqys8e9YxF2Jw505kW2tNW7UAucwQ9tS9MXCRbGwAkCX5Kpd5i1pDLP2r+WCSsqFRvwj7dtRom3dLwszWpNEgTKeOxMx9lP5jkptfhOZRWyjVPIankQTgmu8kLdzODnhszs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HoKv/x5q; 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="HoKv/x5q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1A6BF1F00A3A; Thu, 18 Jun 2026 08:19:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781770761; bh=gqhDjzcGQdhdiLmBswp+dNP5/7Fhe1q9r4L1hH6XVBs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HoKv/x5qawc4vbnWhIlfsU7cwH1p9bEM3g1xxvwHyOcekWMM/TBDs2xjtjxO99qiI 9XBRk3tp2HG7UyUOpbx1jiUYhdqJA7RYrTFlJ09mHzzKR/Ag6odb2C0uy663SPNkT3 +qZOXaLc3qAyKz8fi5DDoWnODwDu/8usmSOuxx/F3P2knL07OdHDVGtt1GPxaoctyZ 1O16iHdbqq3s+37Vb9e6xTiKVRQ6pg7YYqD4l7tKV6nc1n+f3+NK3lT9MCW1xTtNLK FmmK95zIZHxwJ5oZpHVWiJSsxUNqRcy0wGGuGFRrVjKN2n1XBLR6nMsL4tt6muqDT4 pbwv1MmHKoQtg== Message-ID: <5a993689-f730-406d-8515-8bb6025cc851@kernel.org> Date: Thu, 18 Jun 2026 10:19:17 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] userfaultfd: prevent registration of special VMAs To: Mike Rapoport , Andrew Morton , Linus Torvalds Cc: 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 References: <20260617194059.2529406-1-rppt@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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? -- Cheers, David