From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 2C3A520C470 for ; Fri, 11 Oct 2024 12:58:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728651526; cv=none; b=fWCn1sEg3X88KyQQt7RHRVukerFm0/0OIHx/F6fLxJd4P+vtkI5ZP8vDu/ylVOA+oABLHk5tVUD2L9Y1o8nQ+LNJLV46HJqNIONzeDmVuY9UgIKM1LExBjFLrKc677FtunLAe3nc9Knb5WQSzSRksvwfR76I49fKnYC+nZLliLM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728651526; c=relaxed/simple; bh=+7mddZED1wYsecI+uoxMxnniKJWRDPds6zSxyllw4ZQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=AfvPGbuM9mUVfWxb9dTEoOCs/uWhnTeOG/fGW4SSsIDJtxq46Qp0A72rIfQNAbZhGMyuDVqd5wzoiFot0fEm+PRQqPOUrYo0nLlDBJ0VufRNQ1VYzErhGFk08nYhcwXezw1CeoeDhs44WNuYduhIuFOnMCI16IkEiW0cwNHSOZg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=h8HJHi3K; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="h8HJHi3K" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1728651523; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=HymYYfVW1qZz3H508wC+nWBcyxC6MerXDfv7v9abyNQ=; b=h8HJHi3Kh23lxBCpudRKCKWjaI6ThFBxTHh4eTDysVnzMSYjeynTQ+Cbo4pq7W1b09GzMl Dj/BjP8D6p/M/Zh5cYL8j8YxN8tsW6tE+kLi74qv+S9iuiMfp4igmj/fudPCN/OKnzpf3w l7l2jan7VMSPLhcI2lpBBfDngrNvtkI= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-267-jV1BEIkfMPiKH6dpqPkJdA-1; Fri, 11 Oct 2024 08:58:41 -0400 X-MC-Unique: jV1BEIkfMPiKH6dpqPkJdA-1 Received: by mail-wr1-f72.google.com with SMTP id ffacd0b85a97d-37d5016d21eso613808f8f.3 for ; Fri, 11 Oct 2024 05:58:41 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1728651521; x=1729256321; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:from:references:cc:to:subject:user-agent :mime-version:date:message-id:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=HymYYfVW1qZz3H508wC+nWBcyxC6MerXDfv7v9abyNQ=; b=IYrU6l35s2QLDB89HSWVPu6J5DjE6mvo2eYVqvvRFIOdbXG8ff4rhHEnrqvs6NMYi+ 51mPpf2sv/4ujrnrgoch8dDIpc/v7lwH1RozufDWnsbGCI6PDHFsw9VJSXzy4EKrwk6/ hmhoBZgPvrLkydWWVS1ZNZwAM1J6pPyYBN9NYsHkuHeNW6dDYey+P4g97bYUqgJnFGrr 5N/r0aKFuzgpLuM/oA6omimYG10hxf0EkwdEpegDYn3AqVcp3oiCVhEr0PuKuBkgwZYf bauP50iJ0+LiGA0G6yJqu29BEIk/+9t96UIg6FzaIolpp57hxIlo54i/ii8EHSefEVyR w50g== X-Forwarded-Encrypted: i=1; AJvYcCXg9Lvu01rjCHDEoGg4Yr9eWOEetleiu2cKMqZE3X1zEna0pX3/PXKeYx8LTmBoRs6gMm89aSI5TcHt3wk=@vger.kernel.org X-Gm-Message-State: AOJu0YzM1W60zQEIFI99gQKNxYK2Uea4Lzo7Fto0Pk8PxPJIYR0maV92 2FcalELEe2sPDj2IOVfmuoopBLJD1cpN7Kk1xUjkWv4LBAQFP+XTxWdylpD2GHBj1HjrxchHG5K 6+VBCTauXf+4d9X1A0oEmZvZUeH3oioSW1bIRWZj6hCLb6zo3Xw8K66ynjmE8IA== X-Received: by 2002:adf:a111:0:b0:37d:4a80:c395 with SMTP id ffacd0b85a97d-37d551b965dmr1729813f8f.21.1728651520613; Fri, 11 Oct 2024 05:58:40 -0700 (PDT) X-Google-Smtp-Source: AGHT+IE1xS+pAjaQ098/BCA16JIYTmXKgXmYVulc5ENoXgDJM+UuCSTduUy8KRzdbADsXgm3sUTwlA== X-Received: by 2002:adf:a111:0:b0:37d:4a80:c395 with SMTP id ffacd0b85a97d-37d551b965dmr1729779f8f.21.1728651520150; Fri, 11 Oct 2024 05:58:40 -0700 (PDT) Received: from ?IPV6:2003:cb:c749:9100:c078:eec6:f2f4:dd3b? (p200300cbc7499100c078eec6f2f4dd3b.dip0.t-ipconnect.de. [2003:cb:c749:9100:c078:eec6:f2f4:dd3b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37d4b6a8ac3sm3875758f8f.3.2024.10.11.05.58.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Oct 2024 05:58:39 -0700 (PDT) Message-ID: <63d112d8-62d0-4e95-81f0-3031f990abc4@redhat.com> Date: Fri, 11 Oct 2024 14:58:38 +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: [RFC PATCH 0/7] support for mm-local memory allocations and use it To: "Mediouni, Mohamed" Cc: "Mehanna, Fares" , "akpm@linux-foundation.org" , "ardb@kernel.org" , "arnd@arndb.de" , "bhelgaas@google.com" , "broonie@kernel.org" , "catalin.marinas@arm.com" , "james.morse@arm.com" , "javierm@redhat.com" , "jean-philippe@linaro.org" , "joey.gouly@arm.com" , "kristina.martsenko@arm.com" , "kvmarm@lists.linux.dev" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "mark.rutland@arm.com" , "maz@kernel.org" , "nh-open-source@amazon.com" , "oliver.upton@linux.dev" , "ptosi@google.com" , "rdunlap@infradead.org" , "Kagan, Roman" , "rppt@kernel.org" , "shikemeng@huaweicloud.com" , "suzuki.poulose@arm.com" , "tabba@google.com" , "will@kernel.org" , "yuzenghui@huawei.com" References: <813b9bcb-afde-40b6-a604-cdb71b4b6d7a@redhat.com> <20241010155210.13321-1-faresx@amazon.de> <465ce78b-d023-40e6-b066-5e4a01e266b6@redhat.com> <6E620679-FC47-4B13-BEF6-B63975881CCD@amazon.de> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 11.10.24 14:56, Mediouni, Mohamed wrote: > > >> On 11. Oct 2024, at 14:36, Mediouni, Mohamed wrote: >> >> >> >>> On 11. Oct 2024, at 14:04, David Hildenbrand wrote: >>> >>> On 10.10.24 17:52, Fares Mehanna wrote: >>>>>> In a series posted a few years ago [1], a proposal was put forward to allow the >>>>>> kernel to allocate memory local to a mm and thus push it out of reach for >>>>>> current and future speculation-based cross-process attacks. We still believe >>>>>> this is a nice thing to have. >>>>>> >>>>>> However, in the time passed since that post Linux mm has grown quite a few new >>>>>> goodies, so we'd like to explore possibilities to implement this functionality >>>>>> with less effort and churn leveraging the now available facilities. >>>>>> >>>>>> An RFC was posted few months back [2] to show the proof of concept and a simple >>>>>> test driver. >>>>>> >>>>>> In this RFC, we're using the same approach of implementing mm-local allocations >>>>>> piggy-backing on memfd_secret(), using regular user addresses but pinning the >>>>>> pages and flipping the user/supervisor flag on the respective PTEs to make them >>>>>> directly accessible from kernel. >>>>>> In addition to that we are submitting 5 patches to use the secret memory to hide >>>>>> the vCPU gp-regs and fp-regs on arm64 VHE systems. >>>>> >>>>> I'm a bit lost on what exactly we want to achieve. The point where we >>>>> start flipping user/supervisor flags confuses me :) >>>>> >>>>> With secretmem, you'd get memory allocated that >>>>> (a) Is accessible by user space -- mapped into user space. >>>>> (b) Is inaccessible by kernel space -- not mapped into the direct map >>>>> (c) GUP will fail, but copy_from / copy_to user will work. >>>>> >>>>> >>>>> Another way, without secretmem, would be to consider these "secrets" >>>>> kernel allocations that can be mapped into user space using mmap() of a >>>>> special fd. That is, they wouldn't have their origin in secretmem, but >>>>> in KVM as a kernel allocation. It could be achieved by using VM_MIXEDMAP >>>>> with vm_insert_pages(), manually removing them from the directmap. >>>>> >>>>> But, I am not sure who is supposed to access what. Let's explore the >>>>> requirements. I assume we want: >>>>> >>>>> (a) Pages accessible by user space -- mapped into user space. >>>>> (b) Pages inaccessible by kernel space -- not mapped into the direct map >>>>> (c) GUP to fail (no direct map). >>>>> (d) copy_from / copy_to user to fail? >>>>> >>>>> And on top of that, some way to access these pages on demand from kernel >>>>> space? (temporary CPU-local mapping?) >>>>> >>>>> Or how would the kernel make use of these allocations? >>>>> >>>>> -- >>>>> Cheers, >>>>> >>>>> David / dhildenb >>>> Hi David, >>> >>> Hi Fares! >>> >>>> Thanks for taking a look at the patches! >>>> We're trying to allocate a kernel memory that is accessible to the kernel but >>>> only when the context of the process is loaded. >>>> So this is a kernel memory that is not needed to operate the kernel itself, it >>>> is to store & process data on behalf of a process. The requirement for this >>>> memory is that it would never be touched unless the process is scheduled on this >>>> core. otherwise any other access will crash the kernel. >>>> So this memory should only be directly readable and writable by the kernel, but >>>> only when the process context is loaded. The memory shouldn't be readable or >>>> writable by the owner process at all. >>>> This is basically done by removing those pages from kernel linear address and >>>> attaching them only in the process mm_struct. So during context switching the >>>> kernel loses access to the secret memory scheduled out and gain access to the >>>> new process secret memory. >>>> This generally protects against speculation attacks, and if other process managed >>>> to trick the kernel to leak data from memory. In this case the kernel will crash >>>> if it tries to access other processes secret memory. >>>> Since this memory is special in the sense that it is kernel memory but only make >>>> sense in the term of the owner process, I tried in this patch series to explore >>>> the possibility of reusing memfd_secret() to allocate this memory in user virtual >>>> address space, manage it in a VMA, flipping the permissions while keeping the >>>> control of the mapping exclusively with the kernel. >>>> Right now it is: >>>> (a) Pages not accessible by user space -- even though they are mapped into user >>>> space, the PTEs are marked for kernel usage. >>> >>> Ah, that is the detail I was missing, now I see what you are trying to achieve, thanks! >>> >>> It is a bit architecture specific, because ... imagine architectures that have separate kernel+user space page table hierarchies, and not a simple PTE flag to change access permissions between kernel/user space. >>> >>> IIRC s390 is one such architecture that uses separate page tables for the user-space + kernel-space portions. >>> >>>> (b) Pages accessible by kernel space -- even though they are not mapped into the >>>> direct map, the PTEs in uvaddr are marked for kernel usage. >>>> (c) copy_from / copy_to user won't fail -- because it is in the user range, but >>>> this can be fixed by allocating specific range in user vaddr to this feature >>>> and check against this range there. >>>> (d) The secret memory vaddr is guessable by the owner process -- that can also >>>> be fixed by allocating bigger chunk of user vaddr for this feature and >>>> randomly placing the secret memory there. >>>> (e) Mapping is off-limits to the owner process by marking the VMA as locked, >>>> sealed and special. >>> >>> Okay, so in this RFC you are jumping through quite some hoops to have a kernel allocation unmapped from the direct map but mapped into a per-process page table only accessible by kernel space. :) >>> >>> So you really don't want this mapped into user space at all (consequently, no GUP, no access, no copy_from_user ...). In this RFC it's mapped but turned inaccessible by flipping the "kernel vs. user" switch. >>> >>>> Other alternative (that was implemented in the first submission) is to track those >>>> allocations in a non-shared kernel PGD per process, then handle creating, forking >>>> and context-switching this PGD. >>> >>> That sounds like a better approach. So we would remove the pages from the shared kernel direct map and map them into a separate kernel-portion in the per-MM page tables? >>> >>> Can you envision that would also work with architectures like s390x? I assume we would not only need the per-MM user space page table hierarchy, but also a per-MM kernel space page table hierarchy, into which we also map the common/shared-among-all-processes kernel space page tables (e.g., directmap). >> Yes, that’s also applicable to arm64. There’s currently no separate per-mm user space page hierarchy there. > typo, read kernel Okay, thanks. So going into that direction makes more sense. I do wonder if we really have to deal with fork() ... if the primary users don't really have meaning in the forked child (e.g., just like fork() with KVM IIRC) we might just get away by "losing" these allocations in the child process. Happy to learn why fork() must be supported. -- Cheers, David / dhildenb