Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934148AbdC3RiD (ORCPT ); Thu, 30 Mar 2017 13:38:03 -0400 Received: from mail-it0-f44.google.com ([209.85.214.44]:35280 "EHLO mail-it0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933259AbdC3RiB (ORCPT ); Thu, 30 Mar 2017 13:38:01 -0400 MIME-Version: 1.0 In-Reply-To: <3890813c-c891-89a5-c16f-66240a794319@redhat.com> References: <3890813c-c891-89a5-c16f-66240a794319@redhat.com> From: Kees Cook Date: Thu, 30 Mar 2017 10:37:58 -0700 X-Google-Sender-Auth: Cq3C9whDwPENam0pG0wgYUGIctQ Message-ID: Subject: Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! To: Laura Abbott Cc: Tommi Rantala , Linux-MM , LKML , Ingo Molnar , Josh Poimboeuf , Mark Rutland , Eric Biggers , Dave Jones Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1865 Lines: 55 On Thu, Mar 30, 2017 at 10:27 AM, Laura Abbott wrote: > On 03/30/2017 09:45 AM, 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. >> >>> [...] >>> [ 51.419063] Call Trace: >>> [ 51.419066] read_mem+0x70/0x120 >>> [ 51.419069] __vfs_read+0x28/0x130 >>> [ 51.419072] ? security_file_permission+0x9b/0xb0 >>> [ 51.419075] ? rw_verify_area+0x4e/0xb0 >>> [ 51.419077] vfs_read+0x96/0x130 >>> [ 51.419079] SyS_read+0x46/0xb0 >>> [ 51.419082] ? SyS_lseek+0x87/0xb0 >>> [ 51.419085] entry_SYSCALL_64_fastpath+0x1a/0xa9 >> >> I can't reproduce this myself, so I assume it's some specific /proc or >> /sys file that I don't have. Are you able to get a strace of x86info >> as it runs to see which file it is attempting to read here? > > I can't see this on any of my Fedora systems. It looks like this > is trying to read /dev/mem so I suspect your BIOS is putting out > unexpected values. If you turn off hardened usercopy does x86info > give you reasonable values? I'd also echo getting an strace. Reads out of /dev/mem should be restricted to non-RAM on Fedora, yes? Tommi, do your kernels have CONFIG_STRICT_DEVMEM=y ? -Kees -- Kees Cook Pixel Security