From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C472EC32772 for ; Tue, 23 Aug 2022 13:09:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 030068D0001; Tue, 23 Aug 2022 09:09:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EFA276B0074; Tue, 23 Aug 2022 09:09:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D4D1C8D0001; Tue, 23 Aug 2022 09:09:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id BF5976B0073 for ; Tue, 23 Aug 2022 09:09:29 -0400 (EDT) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 85C581C69B7 for ; Tue, 23 Aug 2022 13:09:29 +0000 (UTC) X-FDA: 79830888858.30.67C79DF Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf07.hostedemail.com (Postfix) with ESMTP id 1563A40051 for ; Tue, 23 Aug 2022 13:09:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1661260167; 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; bh=w8kdBKGl71weZmKn4bSKogcjlxbB109HsgGUffsIt0g=; b=AOqcjs+t4UzvsWsGeH7n+KvaqmCiPXZLs3fiqx3tSmE3v7OUElsxX6q9S/dHD2lnm58RE6 NO516N/cUl7nBcdr47yB+kfVwDyMN1MFCrFUIC6xxmEC0lvt8dP5+6/T9QRsOlATlFAX4l q3bT1BQ5yTESbuGsy7LEeSbo7fDIAPo= 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_128_GCM_SHA256) id us-mta-530-Nq15MA09Mv2yFxIAnvFJSg-1; Tue, 23 Aug 2022 09:09:26 -0400 X-MC-Unique: Nq15MA09Mv2yFxIAnvFJSg-1 Received: by mail-wr1-f72.google.com with SMTP id l25-20020adfa399000000b002252058bad2so2251326wrb.11 for ; Tue, 23 Aug 2022 06:09:26 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:in-reply-to:subject:organization:from :references:cc:to:content-language:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc; bh=w8kdBKGl71weZmKn4bSKogcjlxbB109HsgGUffsIt0g=; b=l5DctB58rFTi6CJjSgY0Rms/hQ9ByI9RAH76u6Zwr2wcv5YVdSHnZEaLnaZ+BjLPR8 bFvaZWfX+XNKeG0uc9Vc6+CJzD3oFMUAKdPDjzpmnIdTXXd6gL5ciXuqGmildZKm2dpj BcZYBEk+7A5evEOo6o/QNRqVqyQqpI2Ignnz7QbFexFDMpaOyzLCOfCzn9qD+1G1cUug e97G61RVlRZDbWB5vHp0WgekDbzj6jEAZszraNAGINf0Vf17r8M5b5L6Hc4r+XZlI8sO ESB/ocGhA6OLAwkDUhN/f6CZ1VhZSOtQ6fbtz5H+8zmepNy4YWqW1uFpJVyz00ZVDjdH RP1A== X-Gm-Message-State: ACgBeo2LagnvybbDHD/oYbLCbORApCXLPsXEz5oNterxgz4uIEaU6wUO /XdzoqrOXGAiLpTaAqKZWAzt9vWr7JcQSW6eXhfTF2QMq2msfrihf5cTkXzehpsfsP3FlAzr1rl mx+S1PiE9g4M= X-Received: by 2002:a05:600c:410d:b0:3a6:1db8:b419 with SMTP id j13-20020a05600c410d00b003a61db8b419mr2143756wmi.119.1661260165330; Tue, 23 Aug 2022 06:09:25 -0700 (PDT) X-Google-Smtp-Source: AA6agR5mU7Ez4PSLMJo2g7PEaUmbNkIKfYQ+V6Bi9Vnw+oGoFj3xX1dzdH4M0PuWRhEY0Mq4I2cEiA== X-Received: by 2002:a05:600c:410d:b0:3a6:1db8:b419 with SMTP id j13-20020a05600c410d00b003a61db8b419mr2143724wmi.119.1661260164944; Tue, 23 Aug 2022 06:09:24 -0700 (PDT) Received: from ?IPV6:2003:cb:c70b:1600:c48b:1fab:a330:5182? (p200300cbc70b1600c48b1faba3305182.dip0.t-ipconnect.de. [2003:cb:c70b:1600:c48b:1fab:a330:5182]) by smtp.gmail.com with ESMTPSA id r1-20020a0560001b8100b002253d865715sm11072769wru.87.2022.08.23.06.09.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Aug 2022 06:09:24 -0700 (PDT) Message-ID: <01fd2b11-513d-eb91-5ce6-fcaa198f8d28@redhat.com> Date: Tue, 23 Aug 2022 15:09:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 To: Charan Teja Kalla , akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz, pasha.tatashin@soleen.com, shakeelb@google.com, sieberf@amazon.com, sjpark@amazon.de, william.kucharski@oracle.com, willy@infradead.org, quic_pkondeti@quicinc.com, minchan@google.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <1660830600-9068-1-git-send-email-quic_charante@quicinc.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH V4] mm: fix use-after free of page_ext after race with memory-offline In-Reply-To: <1660830600-9068-1-git-send-email-quic_charante@quicinc.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1661260168; a=rsa-sha256; cv=none; b=YLthqyx49MWuCmdMockMehveIWr51Rq5RxMoYhCHkmA7phM05JElsP1ozN999P465en9QJ xjvoynvfeeuKB7s6ep2geQPIr4Or95JCcn94Hhrq8TaZtC40b+4ujBA2XMLYXy+H8E5J28 SzscMoWWgetfYd80auithdRqFj1BVbI= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=AOqcjs+t; spf=pass (imf07.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 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=1661260168; 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=w8kdBKGl71weZmKn4bSKogcjlxbB109HsgGUffsIt0g=; b=V1HCjT+SJEx7FAuV5M9cEtt3vUe/k+C7yJHMtLmwt0NgE6TpsG1DdIeTPQvrfC9P/yAPwj x7ogCTgTsLsdCRKbZIxmKB6C1KDxeBRXc4t5K1epeVZSNrLhMtKHE6NLKD2hY4SGEFiQzs NbvTVeVsR1wndc4xjUJroh0hszxx45M= X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 1563A40051 Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=AOqcjs+t; spf=pass (imf07.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: uq4t5wzfbxfwmkb3hqdr1a1xi5n7om4d X-HE-Tag: 1661260167-802026 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 18.08.22 15:50, Charan Teja Kalla wrote: > The below is one path where race between page_ext and offline of the > respective memory blocks will cause use-after-free on the access of > page_ext structure. > > process1 process2 > --------- --------- > a)doing /proc/page_owner doing memory offline > through offline_pages. > > b)PageBuddy check is failed > thus proceed to get the > page_owner information > through page_ext access. > page_ext = lookup_page_ext(page); > > migrate_pages(); > ................. > Since all pages are successfully > migrated as part of the offline > operation,send MEM_OFFLINE notification > where for page_ext it calls: > offline_page_ext()--> > __free_page_ext()--> > free_page_ext()--> > vfree(ms->page_ext) > mem_section->page_ext = NULL > > c) Check for the PAGE_EXT flags > in the page_ext->flags access > results into the use-after-free(leading > to the translation faults). > > As mentioned above, there is really no synchronization between page_ext > access and its freeing in the memory_offline. > > The memory offline steps(roughly) on a memory block is as below: > 1) Isolate all the pages > 2) while(1) > try free the pages to buddy.(->free_list[MIGRATE_ISOLATE]) > 3) delete the pages from this buddy list. > 4) Then free page_ext.(Note: The struct page is still alive as it is > freed only during hot remove of the memory which frees the memmap, which > steps the user might not perform). > > This design leads to the state where struct page is alive but the struct > page_ext is freed, where the later is ideally part of the former which > just representing the page_flags (check [3] for why this design is > chosen). > > The above mentioned race is just one example __but the problem persists > in the other paths too involving page_ext->flags access(eg: > page_is_idle())__. > > Fix all the paths where offline races with page_ext access by > maintaining synchronization with rcu lock and is achieved in 3 steps: > 1) Invalidate all the page_ext's of the sections of a memory block by > storing a flag in the LSB of mem_section->page_ext. > > 2) Wait till all the existing readers to finish working with the > ->page_ext's with synchronize_rcu(). Any parallel process that starts > after this call will not get page_ext, through lookup_page_ext(), for > the block parallel offline operation is being performed. > > 3) Now safely free all sections ->page_ext's of the block on which > offline operation is being performed. > > Note: If synchronize_rcu() takes time then optimizations can be done in > this path through call_rcu()[2]. > > Thanks to David Hildenbrand for his views/suggestions on the initial > discussion[1] and Pavan kondeti for various inputs on this patch. > > [1] https://lore.kernel.org/linux-mm/59edde13-4167-8550-86f0-11fc67882107@quicinc.com/ > [2] https://lore.kernel.org/all/a26ce299-aed1-b8ad-711e-a49e82bdd180@quicinc.com/T/#u > [3] https://lore.kernel.org/all/6fa6b7aa-731e-891c-3efb-a03d6a700efa@redhat.com/ > > Suggested-by: David Hildenbrand > Suggested-by: Michal Hocko > Signed-off-by: Charan Teja Kalla In general, LGTM, one comment below. > > static ssize_t > @@ -508,6 +527,14 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) > /* Find an allocated page */ > for (; pfn < max_pfn; pfn++) { > /* > + * This temporary page_owner is required so > + * that we can avoid the context switches while holding > + * the rcu lock and copying the page owner information to > + * user through copy_to_user() or GFP_KERNEL allocations. > + */ > + struct page_owner page_owner_tmp; > + > + /* > * If the new page is in a new MAX_ORDER_NR_PAGES area, > * validate the area as existing, skip it if not > */ > @@ -525,7 +552,7 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) > continue; > } > > - page_ext = lookup_page_ext(page); > + page_ext = page_ext_get(page); > if (unlikely(!page_ext)) > continue; > > @@ -534,14 +561,14 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) > * because we don't hold the zone lock. > */ > if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) > - continue; > + goto loop; > > /* > * Although we do have the info about past allocation of free > * pages, it's not relevant for current memory usage. > */ > if (!test_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags)) > - continue; > + goto loop; > > page_owner = get_page_owner(page_ext); > > @@ -550,7 +577,7 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) > * would inflate the stats. > */ > if (!IS_ALIGNED(pfn, 1 << page_owner->order)) > - continue; > + goto loop; > > /* > * Access to page_ext->handle isn't synchronous so we should > @@ -558,13 +585,17 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) > */ > handle = READ_ONCE(page_owner->handle); > if (!handle) > - continue; > + goto loop; > > /* Record the next PFN to read in the file offset */ > *ppos = (pfn - min_low_pfn) + 1; > > + page_owner_tmp = *page_owner; > + page_ext_put(page_ext); > return print_page_owner(buf, count, pfn, page, > - page_owner, handle); > + &page_owner_tmp, handle); > +loop: > + page_ext_put(page_ext); > } > > return 0; > @@ -617,18 +648,20 @@ static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone) > if (PageReserved(page)) > continue; > > - page_ext = lookup_page_ext(page); > + page_ext = page_ext_get(page); > if (unlikely(!page_ext)) > continue; > > /* Maybe overlapping zone */ > if (test_bit(PAGE_EXT_OWNER, &page_ext->flags)) > - continue; > + goto loop; > > /* Found early allocated page */ > __set_page_owner_handle(page_ext, early_handle, > 0, 0); > count++; > +loop: > + page_ext_put(page_ext); > } I kind-of dislike the "loop" labels. Can we come up with a more expressive name? "put_continue" or something? One alternative would be to add to the beginning of the loop, and after the loop sth like if (page_ext) { page_ext_put(page_ext); page_ext = NULL; } One could wrap that in a function, but not sure if that improves the situation. -- Thanks, David / dhildenb