From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f197.google.com (mail-qt0-f197.google.com [209.85.216.197]) by kanga.kvack.org (Postfix) with ESMTP id C6B626B0397 for ; Fri, 31 Mar 2017 13:17:28 -0400 (EDT) Received: by mail-qt0-f197.google.com with SMTP id q46so27254518qtb.16 for ; Fri, 31 Mar 2017 10:17:28 -0700 (PDT) Received: from scorn.kernelslacker.org (scorn.kernelslacker.org. [2600:3c03::f03c:91ff:fe59:ec69]) by mx.google.com with ESMTPS id n62si5140532qkf.156.2017.03.31.10.17.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 31 Mar 2017 10:17:27 -0700 (PDT) Date: Fri, 31 Mar 2017 13:17:24 -0400 From: Dave Jones Subject: Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Message-ID: <20170331171724.nm22iqiellfsvj5z@codemonkey.org.uk> References: <20170330194143.cbracica3w3ijrcx@codemonkey.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Kees Cook Cc: Tommi Rantala , Linux-MM , LKML , Laura Abbott , Ingo Molnar , Josh Poimboeuf , Mark Rutland , Eric Biggers On Thu, Mar 30, 2017 at 12:52:31PM -0700, Kees Cook wrote: > On Thu, Mar 30, 2017 at 12:41 PM, Dave Jones wrote: > > On Thu, Mar 30, 2017 at 09:45:26AM -0700, Kees Cook wrote: > > > On Wed, Mar 29, 2017 at 11:44 PM, Tommi Rantala > > > wrote: > > > > Hi, > > > > > > > > Running: > > > > > > > > $ sudo x86info -a > > > > > > > > On this HP ZBook 15 G3 laptop kills the x86info process with segfault and > > > > produces the following kernel BUG. > > > > > > > > $ git describe > > > > v4.11-rc4-40-gfe82203 > > > > > > > > It is also reproducible with the fedora kernel: 4.9.14-200.fc25.x86_64 > > > > > > > > Full dmesg output here: https://pastebin.com/raw/Kur2mpZq > > > > > > > > [ 51.418954] usercopy: kernel memory exposure attempt detected from > > > > ffff880000090000 (dma-kmalloc-256) (4096 bytes) > > > > > > This seems like a real exposure: the copy is attempting to read 4096 > > > bytes from a 256 byte object. > > > > The code[1] is doing a 4k read from /dev/mem in the range 0x90000 -> 0xa0000 > > According to arch/x86/mm/init.c:devmem_is_allowed, that's still valid.. > > > > Note that the printk is using the direct mapping address. Is that what's > > being passed down to devmem_is_allowed now ? If so, that's probably what broke. > > So this is attempting to read physical memory 0x90000 -> 0xa0000, but > that's somehow resolving to a virtual address that is claimed by > dma-kmalloc?? I'm confused how that's happening... /dev/mem is using physical addresses that the kernel translates through the direct mapping. __check_object_size seems to think that anything passed into it is always allocated by the kernel, but in this case, I think read_mem() is just passing through the direct mapping to copy_to_user. Dave -- 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