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[2003:cb:c709:8000:b502:8c1c:3624:99d4]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37cd566a41fsm2476804f8f.45.2024.09.27.05.59.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 27 Sep 2024 05:59:41 -0700 (PDT) Message-ID: <813b9bcb-afde-40b6-a604-cdb71b4b6d7a@redhat.com> Date: Fri, 27 Sep 2024 14:59:39 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/7] support for mm-local memory allocations and use it To: Fares Mehanna Cc: nh-open-source@amazon.com, Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Andrew Morton , Kemeng Shi , =?UTF-8?Q?Pierre-Cl=C3=A9ment_Tosi?= , Ard Biesheuvel , Mark Rutland , Javier Martinez Canillas , Arnd Bergmann , Fuad Tabba , Mark Brown , Joey Gouly , Kristina Martsenko , Randy Dunlap , Bjorn Helgaas , Jean-Philippe Brucker , "Mike Rapoport (IBM)" , Roman Kagan , "moderated list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" , "open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" , open list , "open list:MEMORY MANAGEMENT" References: <20240911143421.85612-1-faresx@amazon.de> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 90212A0011 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: kidb1wgbwmrq3a5jg5r5zx64iad1gzr1 X-HE-Tag: 1727441986-951789 X-HE-Meta: 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 QjmdBFA+ jxY6spVZbTQUmoFbZ2RSiOMkJN2s1JaCEKSprJ+5y3npIyq4F/SKfDvDBr4TygXpfmwosF+bOHxIT4v3TgxRNuJ/aN/dtbDKNsgN8NYmyrenDKctnpN+PSmHxFrbYnCn2YPplR8DUUUYQSQnva7kDT1WhEVtuLTuGnE5wH/XivePIBLagtZ9uTpN6GCGqvk7hxnUKhsHeJImVi6QyJsRgThx3CAduSvPt0SMIQn79NZAHZ+/4BJ4OiPrnjDtdgSPloHrLbxYb+HyAmho9Xb9kwDM6+PoBNbN8xSf3uXqNkWUnV1rvm7wKXlheP1yNEscib9TRsqEAkDPqqvhT7BsQ+genQRHf0AQCltCb26Jbn/ESod5AjKWRBba8m208SwK4hjsk5Deyf63ce4dHfm+Jw7GFsQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11.09.24 16:33, 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