From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 399956B0038 for ; Fri, 31 Mar 2017 01:40:08 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id m33so14152275wrm.23 for ; Thu, 30 Mar 2017 22:40:08 -0700 (PDT) Received: from EUR01-VE1-obe.outbound.protection.outlook.com (mail-ve1eur01on0135.outbound.protection.outlook.com. [104.47.1.135]) by mx.google.com with ESMTPS id 10si6613993wrt.64.2017.03.30.22.40.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 30 Mar 2017 22:40:06 -0700 (PDT) Subject: Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! References: <20170330194143.cbracica3w3ijrcx@codemonkey.org.uk> <20170330200100.zcyndf3kimepg77o@codemonkey.org.uk> From: Tommi Rantala Message-ID: <81379c63-674c-a37f-a6f6-5af385138a25@nokia.com> Date: Fri, 31 Mar 2017 08:40:00 +0300 MIME-Version: 1.0 In-Reply-To: <20170330200100.zcyndf3kimepg77o@codemonkey.org.uk> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Jones , Kees Cook , Linux-MM , LKML , Laura Abbott , Ingo Molnar , Josh Poimboeuf , Mark Rutland , Eric Biggers On 30.03.2017 23:01, Dave Jones wrote: > 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... > > The only thing that I can think of would be a rogue ptr in the bios > table, but that seems unlikely. Tommi, can you put strace of x86info -mp somewhere? > That will confirm/deny whether we're at least asking the kernel to do sane things. Indeed the bug happens when reading from /dev/mem: https://pastebin.com/raw/ZEJGQP1X # strace -f -y x86info -mp [...] open("/dev/mem", O_RDONLY) = 3 lseek(3, 1038, SEEK_SET) = 1038 read(3, "\300\235", 2) = 2 lseek(3, 646144, SEEK_SET) = 646144 read(3, "\1\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024 lseek(3, 1043, SEEK_SET) = 1043 read(3, "w\2", 2) = 2 lseek(3, 645120, SEEK_SET) = 645120 read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024 lseek(3, 654336, SEEK_SET) = 654336 read(3, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024 lseek(3, 983040, SEEK_SET) = 983040 read(3, "IFE$\245S\0\0\1\0\0\0\0\360y\0\0\360\220\260\30\237{=\23\10\17\0000\276\17\0"..., 65536) = 65536 lseek(3, 917504, SEEK_SET) = 917504 read(3, "\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377"..., 65536) = 65536 lseek(3, 524288, SEEK_SET) = 524288 read(3, ) = ? +++ killed by SIGSEGV +++ -- 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