From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f48.google.com (mail-wm0-f48.google.com [74.125.82.48]) by kanga.kvack.org (Postfix) with ESMTP id 4666C828F4 for ; Tue, 9 Feb 2016 07:27:22 -0500 (EST) Received: by mail-wm0-f48.google.com with SMTP id p63so20865929wmp.1 for ; Tue, 09 Feb 2016 04:27:22 -0800 (PST) Received: from david.siemens.de (david.siemens.de. [192.35.17.14]) by mx.google.com with ESMTPS id l11si22828744wmd.29.2016.02.09.04.27.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 09 Feb 2016 04:27:21 -0800 (PST) Date: Tue, 9 Feb 2016 13:26:45 +0100 From: Henning Schild Subject: Re: [PATCH] x86/mm/vmfault: Make vmalloc_fault() handle large pages Message-ID: <20160209132645.55971eff@md1em3qc> In-Reply-To: <20160209102235.GA9885@gmail.com> References: <1454976038-22486-1-git-send-email-toshi.kani@hpe.com> <20160209091003.GA10774@gmail.com> <20160209105325.0ce9a104@md1em3qc> <20160209102235.GA9885@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar Cc: Toshi Kani , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, bp@alien8.de, linux-nvdimm@lists.01.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, 9 Feb 2016 11:22:35 +0100 Ingo Molnar wrote: > * 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 ?? Looking over the code again i am not sure the last two are even possible, it is just the pointer deref that can cause a #PF. If the pointer turns out to "work" the code will just read and eventually BUG(). > 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 -- 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