From patchwork Thu Apr 1 18:21:25 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 414273 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT, USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 09860C433ED for ; Thu, 1 Apr 2021 19:22:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D8F2361001 for ; Thu, 1 Apr 2021 19:22:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235030AbhDATWx (ORCPT ); Thu, 1 Apr 2021 15:22:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51212 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234326AbhDATWr (ORCPT ); Thu, 1 Apr 2021 15:22:47 -0400 Received: from mail-qv1-xf49.google.com (mail-qv1-xf49.google.com [IPv6:2607:f8b0:4864:20::f49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0CFA1C049FD1 for ; Thu, 1 Apr 2021 11:21:39 -0700 (PDT) Received: by mail-qv1-xf49.google.com with SMTP id gy8so3855913qvb.4 for ; Thu, 01 Apr 2021 11:21:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc:content-transfer-encoding; bh=1v73NpRb4gNLtIJ6f4iTsLt04NK7xDWlZvvGIJeIyOY=; b=BGhVoWtyVDS11um69GvHWaBxjInp0xc3nZ5igQbDAiVstwD+DwfnURZTAVsHvefgul 54CNcu4PR19AQT/0CY7RzNPbivkK8sBS4gr5l9Y8nIqdzfWJXgPSfyuryUbXs1i117CW ypS9RQXBq/eURlzTCMmK5OT5dgKf2sJM9PYhQwlJ24MLApAGorTD0mAVAvC8SCFmekKR rJ53gDagXqpf+orSrLVUX6slrSoSNg32aHBosaupo8IXy6ULWRPhUqVFRP319BpvKy4q 0jADW5Au3xewFYvz4nt8yaXmmPjjO63lVrGa6MCKaHqCIhu3+iCbTWipUikh7ZnmJxXZ YgBw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc:content-transfer-encoding; bh=1v73NpRb4gNLtIJ6f4iTsLt04NK7xDWlZvvGIJeIyOY=; b=tCjhmXAKTd/H8OeqXDOTNnm9PkxbryiQoqMZf2ipnep2XiZQfw25UXzDmKpASrU3VN ZK8gfSDIM6TGCkbllZgB/NrahAOr6PTGZdzgGTqzmSESeXywSMBmrRk1QptDe/5RB1kJ gAYBlhOXetXQpa9BuxXd9EEon7GG2VlUl2Fk5zAR51ng2Pwwfacf2cBhkYNaJpOWBnOa 01KroUwT6SyxiUycUYeltLGbHAEiBoVkfSxtYnJc8W8Lqs2zTHzAoN28fdiWHWOOHG1Y nJU85gqXY9wv+V5v2aRTfmL6cMQcFKS7e6osHFqewI4Sthe1xBqzAP6fpM4/N+hrtUyR rGdw== X-Gm-Message-State: AOAM533jRBKRYlpBbmqVyttqNL3bjWBP8xWaeeywAgO9HKwupLKvYl0i BTteKUNg0EyUvKSKMjX8j+7Dpo6FZtAlaM/XKKSXTRm3xARI/++QsR77GaRoBmvsXaA17oXJhfG QBRgk1JfejQmNDnJinlcPtJz/oQjYY8DOhU73JKvK0UTBbVHYH7BNtz5NQ9lLVg== X-Google-Smtp-Source: ABdhPJwxEkRxWitj7VWGtbxQbGP2KZXXbWNT/3WR7Y0OIP2YMtheTtde/hB1RIvwzNn28Us9gKp/DzrgxuY= X-Received: from surenb1.mtv.corp.google.com ([2620:15c:211:200:899:1066:21fc:b3c5]) (user=surenb job=sendgmr) by 2002:ad4:50c7:: with SMTP id e7mr9408265qvq.58.1617301298047; Thu, 01 Apr 2021 11:21:38 -0700 (PDT) Date: Thu, 1 Apr 2021 11:21:25 -0700 In-Reply-To: <20210401182125.171484-1-surenb@google.com> Message-Id: <20210401182125.171484-6-surenb@google.com> Mime-Version: 1.0 References: <20210401182125.171484-1-surenb@google.com> X-Mailer: git-send-email 2.31.0.291.g576ba9dcdaf-goog Subject: [PATCH 5/5] mm/userfaultfd: fix memory corruption due to writeprotect From: Suren Baghdasaryan To: stable@vger.kernel.org Cc: gregkh@linuxfoundation.org, jannh@google.com, ktkhai@virtuozzo.com, torvalds@linux-foundation.org, shli@fb.com, namit@vmware.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, surenb@google.com, Yu Zhao , Peter Xu , Andrea Arcangeli , Andy Lutomirski , Pavel Emelyanov , Mike Kravetz , Mike Rapoport , Minchan Kim , Will Deacon , Peter Zijlstra , Andrew Morton Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Nadav Amit Userfaultfd self-test fails occasionally, indicating a memory corruption. Analyzing this problem indicates that there is a real bug since mmap_lock is only taken for read in mwriteprotect_range() and defers flushes, and since there is insufficient consideration of concurrent deferred TLB flushes in wp_page_copy(). Although the PTE is flushed from the TLBs in wp_page_copy(), this flush takes place after the copy has already been performed, and therefore changes of the page are possible between the time of the copy and the time in which the PTE is flushed. To make matters worse, memory-unprotection using userfaultfd also poses a problem. Although memory unprotection is logically a promotion of PTE permissions, and therefore should not require a TLB flush, the current userrfaultfd code might actually cause a demotion of the architectural PTE permission: when userfaultfd_writeprotect() unprotects memory region, it unintentionally *clears* the RW-bit if it was already set. Note that this unprotecting a PTE that is not write-protected is a valid use-case: the userfaultfd monitor might ask to unprotect a region that holds both write-protected and write-unprotected PTEs. The scenario that happens in selftests/vm/userfaultfd is as follows: cpu0 cpu1 cpu2 ---- ---- ---- [ Writable PTE cached in TLB ] userfaultfd_writeprotect() [ write-*unprotect* ] mwriteprotect_range() mmap_read_lock() change_protection() change_protection_range() ... change_pte_range() [ *clear* “write”-bit ] [ defer TLB flushes ] [ page-fault ] ... wp_page_copy() cow_user_page() [ copy page ] [ write to old page ] ... set_pte_at_notify() A similar scenario can happen: cpu0 cpu1 cpu2 cpu3 ---- ---- ---- ---- [ Writable PTE cached in TLB ] userfaultfd_writeprotect() [ write-protect ] [ deferred TLB flush ] userfaultfd_writeprotect() [ write-unprotect ] [ deferred TLB flush] [ page-fault ] wp_page_copy() cow_user_page() [ copy page ] ... [ write to page ] set_pte_at_notify() This race exists since commit 292924b26024 ("userfaultfd: wp: apply _PAGE_UFFD_WP bit"). Yet, as Yu Zhao pointed, these races became apparent since commit 09854ba94c6a ("mm: do_wp_page() simplification") which made wp_page_copy() more likely to take place, specifically if page_count(page) > 1. To resolve the aforementioned races, check whether there are pending flushes on uffd-write-protected VMAs, and if there are, perform a flush before doing the COW. Further optimizations will follow to avoid during uffd-write-unprotect unnecassary PTE write-protection and TLB flushes. Link: https://lkml.kernel.org/r/20210304095423.3825684-1-namit@vmware.com Fixes: 09854ba94c6a ("mm: do_wp_page() simplification") Signed-off-by: Nadav Amit Suggested-by: Yu Zhao Reviewed-by: Peter Xu Tested-by: Peter Xu Cc: Andrea Arcangeli Cc: Andy Lutomirski Cc: Pavel Emelyanov Cc: Mike Kravetz Cc: Mike Rapoport Cc: Minchan Kim Cc: Will Deacon Cc: Peter Zijlstra Cc: [5.9+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memory.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index 656d90a75cf8..fe6e92de9bec 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2825,6 +2825,14 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) { struct vm_area_struct *vma = vmf->vma; + /* + * Userfaultfd write-protect can defer flushes. Ensure the TLB + * is flushed in this case before copying. + */ + if (unlikely(userfaultfd_wp(vmf->vma) && + mm_tlb_flush_pending(vmf->vma->vm_mm))) + flush_tlb_page(vmf->vma, vmf->address); + vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte); if (!vmf->page) { /*