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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=ham 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 65E07C5ACCC for ; Tue, 16 Oct 2018 19:17:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 19A8D2087A for ; Tue, 16 Oct 2018 19:17:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="uqU8kyKF" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 19A8D2087A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=efficios.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727188AbeJQDJd (ORCPT ); Tue, 16 Oct 2018 23:09:33 -0400 Received: from mail.efficios.com ([167.114.142.138]:46848 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727007AbeJQDJd (ORCPT ); Tue, 16 Oct 2018 23:09:33 -0400 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 21E251C12ED; Tue, 16 Oct 2018 15:17:39 -0400 (EDT) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id UT-JoZxXY-AE; Tue, 16 Oct 2018 15:17:38 -0400 (EDT) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 601B81C12E5; Tue, 16 Oct 2018 15:17:38 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 601B81C12E5 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1539717458; bh=zjxmfsGc4CKn/xFgwTqUPhXaJI8Odei5l4VSEwnLrrE=; h=Date:From:To:Message-ID:MIME-Version; b=uqU8kyKFC2mZFFxE/j6bCOF/ZyMUuryt6T6qBNm8o5NWJB/D3mn3+1nU1MJiXI+0v XfIjRca8Rgvs79LR55VQbMjN36zQ8vSbU2JFZ2Vwwmb4MYJUdn8AeRJkgatiIdkkfa ao1FaHL8tmBac77qdLGt72MmQ/zoR0Ybw5GGvCv+tThvs5P8eTOHhsG8AuaBl6ZvYv NEn/IFT58xlyZRlU1RcHtXbw7MOCBUZd8d/S5/fXr7QCfysJZXlkrq58/G9i2SVhLd qpFxVRmBEUFfm8YlKetTLgmK/wuYYEQxtM5iSKQIE6qKGucUJZFzElJO6kAnzDyGWW x/4KZSiB9P7rQ== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10026) with ESMTP id B0Brpi0KFSJO; Tue, 16 Oct 2018 15:17:38 -0400 (EDT) Received: from mail02.efficios.com (mail02.efficios.com [167.114.142.138]) by mail.efficios.com (Postfix) with ESMTP id 3AA8F1C12DC; Tue, 16 Oct 2018 15:17:38 -0400 (EDT) Date: Tue, 16 Oct 2018 15:17:37 -0400 (EDT) From: Mathieu Desnoyers To: Sergey Senozhatsky Cc: Peter Zijlstra , "Paul E. McKenney" , Boqun Feng , linux-kernel , linux-api , Thomas Gleixner , Andy Lutomirski , Dave Watson , Paul Turner , Andrew Morton , Russell King , Ingo Molnar , "H. Peter Anvin" , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Will Deacon , Michael Kerrisk , Joel Fernandes Message-ID: <1984292897.263.1539717457933.JavaMail.zimbra@efficios.com> In-Reply-To: <20181016081029.GA30363@jagdpanzerIV> References: <20181010191936.7495-1-mathieu.desnoyers@efficios.com> <20181010191936.7495-7-mathieu.desnoyers@efficios.com> <20181016081029.GA30363@jagdpanzerIV> Subject: Re: [RFC PATCH for 4.21 06/16] cpu_opv: Provide cpu_opv system call (v8) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.10_GA_3039 (ZimbraWebClient - FF52 (Linux)/8.8.10_GA_3041) Thread-Topic: cpu_opv: Provide cpu_opv system call (v8) Thread-Index: vm8UPrPInsgaIqXZLf/bG4IscOuaSA== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Oct 16, 2018, at 4:10 AM, Sergey Senozhatsky sergey.senozhatsky.work@gmail.com wrote: > Hi Mathieu, > > On (10/10/18 15:19), Mathieu Desnoyers wrote: > [..] >> +SYSCALL_DEFINE4(cpu_opv, struct cpu_op __user *, ucpuopv, int, cpuopcnt, >> + int, cpu, int, flags) >> +{ > [..] >> +again: >> + ret = cpu_opv_pin_pages(cpuopv, cpuopcnt, &vaddr_ptrs); >> + if (ret) >> + goto end; >> + ret = do_cpu_opv(cpuopv, cpuopcnt, &vaddr_ptrs, cpu); >> + if (ret == -EAGAIN) >> + retry = true; >> +end: >> + for (i = 0; i < vaddr_ptrs.nr_vaddr; i++) { >> + struct vaddr *vaddr = &vaddr_ptrs.addr[i]; >> + int j; >> + >> + vm_unmap_user_ram((void *)vaddr->mem, vaddr->nr_pages); > > A dumb question. > > Both vm_unmap_user_ram() and vm_map_user_ram() can BUG_ON(). > So this is > userspace -> syscall -> cpu_opv() -> vm_unmap_user_ram() -> BUG_ON() > > Any chance someone can exploit it? Hi Sergey, Let's look at vm_unmap_user_ram() and vm_map_user_ram() separately. If we look at the input from vm_unmap_user_ram, it's called with the following parameters by the cpu_opv system call: for (i = 0; i < vaddr_ptrs.nr_vaddr; i++) { struct vaddr *vaddr = &vaddr_ptrs.addr[i]; int j; vm_unmap_user_ram((void *)vaddr->mem, vaddr->nr_pages); [...] } The vaddr_ptrs array content is filled by the call to cpu_opv_pin_pages above: ret = cpu_opv_pin_pages(cpuopv, cpuopcnt, &vaddr_ptrs); if (ret) goto end; by passing the array to cpu_op_pin_pages(), which appends a virtual address at the end of the array (on success) and increments nr_vaddr. Those virtual addresses are returned by vm_map_user_ram(), so they are not user-controlled. Therefore, only an internal kernel bug between vm_map_user_ram() and vm_unmap_user_ram() should trigger the BUG_ON(). No user input is passed to vm_unmap_user_ram(). Now, let's look at vm_map_user_ram(). It calls alloc_vmap_area(), which returns a vmap_area. Then if vmap_page_range failed, vm_unmap_user_ram is called on the memory that has just been returned by vm_map_user_ram. Again, only an internal bug between map/unmap can trigger the BUG_ON() in vm_unmap_user_ram. Is there another scenario I missed ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com