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[79.242.61.58]) by smtp.gmail.com with ESMTPSA id m20sm1745208wmq.11.2021.11.16.00.02.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 16 Nov 2021 00:02:32 -0800 (PST) Message-ID: <4289b936-e40c-cde8-eb08-0bd13c44eba3@redhat.com> Date: Tue, 16 Nov 2021 09:02:31 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH v2] proc/vmcore: fix clearing user buffer by properly using clear_user() Content-Language: en-US To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Baoquan He , Dave Young , Vivek Goyal , Philipp Rudo , kexec@lists.infradead.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org References: <20211112092750.6921-1-david@redhat.com> <20211115140444.bca2b88cfdd992760a413442@linux-foundation.org> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20211115140444.bca2b88cfdd992760a413442@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 15.11.21 23:04, Andrew Morton wrote: > On Fri, 12 Nov 2021 10:27:50 +0100 David Hildenbrand wrote: > >> To clear a user buffer we cannot simply use memset, we have to use >> clear_user(). With a virtio-mem device that registers a vmcore_cb and has >> some logically unplugged memory inside an added Linux memory block, I can >> easily trigger a BUG by copying the vmcore via "cp": >> >> ... >> >> Some x86-64 CPUs have a CPU feature called "Supervisor Mode Access >> Prevention (SMAP)", which is used to detect wrong access from the kernel to >> user buffers like this: SMAP triggers a permissions violation on wrong >> access. In the x86-64 variant of clear_user(), SMAP is properly >> handled via clac()+stac(). >> >> To fix, properly use clear_user() when we're dealing with a user buffer. >> > > I added cc:stable, OK? > I was a bit hesitant because this would (beofe the virtio-mem changes) only trigger under XEN and I was wondering why nobody notices under XEN so far. But yes, even though it only applies to the kdump kernel, cc:stable sounds like the right think to do! Thanks Andrew! -- Thanks, David / dhildenb