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[2003:cb:c702:9000:3d6:e434:f8b4:80cf]) by smtp.gmail.com with ESMTPSA id j15-20020a5d452f000000b002416e383e1csm11584060wra.25.2022.11.28.09.37.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 28 Nov 2022 09:37:48 -0800 (PST) Message-ID: <66cfc9ba-868c-9620-fbfc-38931c76ff50@redhat.com> Date: Mon, 28 Nov 2022 18:37:47 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.1 Subject: Re: [PATCH v3 3/3] mm/khugepaged: Invoke MMU notifiers in shmem/file collapse paths To: Jann Horn , security@kernel.org, Andrew Morton Cc: Yang Shi , Peter Xu , John Hubbard , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20221125213714.4115729-1-jannh@google.com> <20221125213714.4115729-3-jannh@google.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20221125213714.4115729-3-jannh@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1669657073; a=rsa-sha256; cv=none; b=Zl1TSbQPdSwUjSQMzt4t53KC8ImeIGVP42zJQIugwoEdjdH1boylulWA14VqbGazsLI6Z0 JGNcq1caMUFmHoHmbDB3ys7h2dd09JtdLFD0VOILXwBpx5HngNCX8YC3LFPIBcRFq0I+dJ gI8FwYbDlG2LCVjiUHBOLY8WhmOLQA8= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=DjCOTsXS; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1669657073; h=from:from:sender: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:dkim-signature; bh=jT1tAFSnCzDikHJ9CZbuhgF0BEJlLq1HTdxSmwB6uss=; b=mq6dUeQbj++rjvVft7PezUKWCtQcinJowmq+1LFbNnFRG/7d+TK5kfyl4dUmYhPREA53Yk WZh5vwks3Rm4FiOU6NnAM9Zo8pBazupwmABPFzwI3UWmEb9ZPy0s/oxFyyrBDsbFIUKBf4 4/DV+etPQDaTuATeHkzh7FmBSvFS5Rc= X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 5F33940006 X-Rspam-User: Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=DjCOTsXS; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: m5rwha86m4p6huxzmeqmcjnwjbfbpha7 X-HE-Tag: 1669657073-362699 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 25.11.22 22:37, Jann Horn wrote: > Any codepath that zaps page table entries must invoke MMU notifiers to > ensure that secondary MMUs (like KVM) don't keep accessing pages which > aren't mapped anymore. Secondary MMUs don't hold their own references to > pages that are mirrored over, so failing to notify them can lead to page > use-after-free. > > I'm marking this as addressing an issue introduced in commit f3f0e1d2150b > ("khugepaged: add support of collapse for tmpfs/shmem pages"), but most of > the security impact of this only came in commit 27e1f8273113 ("khugepaged: > enable collapse pmd for pte-mapped THP"), which actually omitted flushes > for the removal of present PTEs, not just for the removal of empty page > tables. > > Cc: stable@kernel.org > Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages") I'm curious, do you have a working reproducer for this? Change looks sane on quick glimpse. -- Thanks, David / dhildenb