From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756585AbcBIKWn (ORCPT ); Tue, 9 Feb 2016 05:22:43 -0500 Received: from mail-wm0-f66.google.com ([74.125.82.66]:32988 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754852AbcBIKWj (ORCPT ); Tue, 9 Feb 2016 05:22:39 -0500 Date: Tue, 9 Feb 2016 11:22:35 +0100 From: Ingo Molnar To: Henning Schild Cc: Toshi Kani , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, bp@alien8.de, linux-nvdimm@ml01.01.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86/mm/vmfault: Make vmalloc_fault() handle large pages Message-ID: <20160209102235.GA9885@gmail.com> References: <1454976038-22486-1-git-send-email-toshi.kani@hpe.com> <20160209091003.GA10774@gmail.com> <20160209105325.0ce9a104@md1em3qc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160209105325.0ce9a104@md1em3qc> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Henning Schild wrote: > On Tue, 9 Feb 2016 10:10:03 +0100 > Ingo Molnar wrote: > > > * Toshi Kani wrote: > > > > > Since 4.1, ioremap() supports large page (pud/pmd) mappings in > > > x86_64 and PAE. vmalloc_fault() however assumes that the vmalloc > > > range is limited to pte mappings. > > > > > > pgd_ctor() sets the kernel's pgd entries to user's during fork(), > > > which makes user processes share the same page tables for the > > > kernel ranges. When a call to ioremap() is made at run-time that > > > leads to allocate a new 2nd level table (pud in 64-bit and pmd in > > > PAE), user process needs to re-sync with the updated kernel pgd > > > entry with vmalloc_fault(). > > > > > > Following changes are made to vmalloc_fault(). > > > > So what were the effects of this shortcoming? Were large page > > ioremap()s unusable? Was this harmless because no driver used this > > facility? > > Drivers do use huge ioremap()s. Now if a pre-existing mm is used to > access the device memory a #PF and the call to vmalloc_fault would > eventually make the kernel treat device memory as if it was a > pagetable. > The results are illegal reads/writes on iomem and dereferencing iomem > content like it was a pointer to a lower level pagetable. > - #PF if you are lucky > - funny modification of arbitrary memory possible > - can be abused with uio or regular userland ?? Ok, so this is a serious live bug exposed to drivers, that also requires a Cc: stable tag. All of this should have been in the changelog! Thanks, Ingo