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[209.85.167.43]) by smtp.gmail.com with ESMTPSA id h4sm537184lfc.97.2020.05.13.16.03.36 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 May 2020 16:03:36 -0700 (PDT) Received: by mail-lf1-f43.google.com with SMTP id v5so906552lfp.13 for ; Wed, 13 May 2020 16:03:36 -0700 (PDT) X-Received: by 2002:ac2:58c8:: with SMTP id u8mr1177915lfo.142.1589411015919; Wed, 13 May 2020 16:03:35 -0700 (PDT) MIME-Version: 1.0 References: <20200513160038.2482415-1-hch@lst.de> <20200513160038.2482415-12-hch@lst.de> <20200513192804.GA30751@lst.de> <0c1a7066-b269-9695-b94a-bb5f4f20ebd8@iogearbox.net> In-Reply-To: <0c1a7066-b269-9695-b94a-bb5f4f20ebd8@iogearbox.net> From: Linus Torvalds Date: Wed, 13 May 2020 16:03:20 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 11/18] maccess: remove strncpy_from_unsafe To: Daniel Borkmann Cc: Christoph Hellwig , "the arch/x86 maintainers" , Alexei Starovoitov , Masami Hiramatsu , Andrew Morton , linux-parisc@vger.kernel.org, linux-um , Netdev , bpf@vger.kernel.org, Linux-MM , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" 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: On Wed, May 13, 2020 at 3:36 PM Daniel Borkmann wrote: > > It's used for both. Daniel, BPF real;ly needs to make up its mind about that. You *cannot* use ti for both. Yes, it happens to work on x86 and some other architectures. But on other architectures, the exact same pointer value can be a kernel pointer or a user pointer. > Given this is enabled on pretty much all program types, my > assumption would be that usage is still more often on kernel memory than user one. You need to pick one. If you know it is a user pointer, use strncpy_from_user() (possibly with disable_pagefault() aka strncpy_from_user_nofault()). And if you know it is a kernel pointer, use strncpy_from_unsafe() (aka strncpy_from_kernel_nofault()). You really can't pick the "randomly one or the other guess what I mean " option. Linus