From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 9 Feb 2016 10:53:25 +0100 From: Henning Schild Subject: Re: [PATCH] x86/mm/vmfault: Make vmalloc_fault() handle large pages Message-ID: <20160209105325.0ce9a104@md1em3qc> In-Reply-To: <20160209091003.GA10774@gmail.com> References: <1454976038-22486-1-git-send-email-toshi.kani@hpe.com> <20160209091003.GA10774@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org 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 List-ID: 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 ?? Henning > If so then the changelog needs to spell this out clearly ... > 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