From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id AF478831FD for ; Tue, 9 May 2017 22:16:57 -0400 (EDT) Received: by mail-pg0-f69.google.com with SMTP id o25so14752964pgc.1 for ; Tue, 09 May 2017 19:16:57 -0700 (PDT) Received: from szxga03-in.huawei.com (szxga03-in.huawei.com. [45.249.212.189]) by mx.google.com with ESMTPS id b6si1636627pfa.364.2017.05.09.19.16.54 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 09 May 2017 19:16:56 -0700 (PDT) Message-ID: <591277AE.80908@huawei.com> Date: Wed, 10 May 2017 10:15:10 +0800 From: Xishi Qiu MIME-Version: 1.0 Subject: Re: [RESENT PATCH] x86/mem: fix the offset overflow when read/write mem References: <1493293775-57176-1-git-send-email-zhongjiang@huawei.com> <1493837167.20270.8.camel@redhat.com> <590A91DF.8030004@huawei.com> <1494344803.20270.27.camel@redhat.com> In-Reply-To: <1494344803.20270.27.camel@redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel Cc: zhong jiang , David Rientjes , Bjorn Helgaas , Yoshinori Sato , Rich Felker , Andrew Morton , arnd@arndb.de, hannes@cmpxchg.org, kirill@shutemov.name, mgorman@techsingularity.net, hughd@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 2017/5/9 23:46, Rik van Riel wrote: > On Thu, 2017-05-04 at 10:28 +0800, zhong jiang wrote: >> On 2017/5/4 2:46, Rik van Riel wrote: > >>> However, it is not as easy as simply checking the >>> end against __pa(high_memory). Some systems have >>> non-contiguous physical memory ranges, with gaps >>> of invalid addresses in-between. >> >> The invalid physical address means that it is used as >> io mapped. not in system ram region. /dev/mem is not >> access to them , is it right? > > Not necessarily. Some systems simply have large > gaps in physical memory access. Their memory map > may look like this: > > |MMMMMM|IO|MMMM|..................|MMMMMMMM| > > Where M is memory, IO is IO space, and the > dots are simply a gap in physical address > space with no valid accesses at all. > Hi Rik, Do you mean IO space is allowed to access from mmap /dev/mem? Thanks, Xishi Qiu >>> At that point, is the complexity so much that it no >>> longer makes sense to try to protect against root >>> crashing the system? >>> >> >> your suggestion is to let the issue along without any protection. >> just root user know what they are doing. > > Well, root already has other ways to crash the system. > > Implementing validation on /dev/mem may make sense if > it can be done in a simple way, but may not be worth > it if it becomes too complex. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org