Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933598AbdCaRcK (ORCPT ); Fri, 31 Mar 2017 13:32:10 -0400 Received: from mail-it0-f54.google.com ([209.85.214.54]:37949 "EHLO mail-it0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933389AbdCaRcH (ORCPT ); Fri, 31 Mar 2017 13:32:07 -0400 MIME-Version: 1.0 In-Reply-To: <20170331171724.nm22iqiellfsvj5z@codemonkey.org.uk> References: <20170330194143.cbracica3w3ijrcx@codemonkey.org.uk> <20170331171724.nm22iqiellfsvj5z@codemonkey.org.uk> From: Kees Cook Date: Fri, 31 Mar 2017 10:32:04 -0700 X-Google-Sender-Auth: Dv5WxYEB_v5KHxCDMl2qT9JWJ0U Message-ID: Subject: Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! To: Dave Jones , Kees Cook , Tommi Rantala , Linux-MM , LKML , Laura Abbott , Ingo Molnar , Josh Poimboeuf , Mark Rutland , Eric Biggers 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: 2568 Lines: 66 On Fri, Mar 31, 2017 at 10:17 AM, 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... > > /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. How is ffff880000090000 both in the direct mapping and a slab object? It would need to pass all of these checks, and be marked as PageSlab before it could be evaluated by __check_heap_object: if (is_vmalloc_or_module_addr(ptr)) return NULL; if (!virt_addr_valid(ptr)) return NULL; page = virt_to_head_page(ptr); /* Check slab allocator for flags and size. */ if (PageSlab(page)) return __check_heap_object(ptr, n, page); -Kees -- Kees Cook Pixel Security