From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 8B08B6B0253 for ; Wed, 13 Dec 2017 07:57:43 -0500 (EST) Received: by mail-wm0-f70.google.com with SMTP id p190so1168335wmd.0 for ; Wed, 13 Dec 2017 04:57:43 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id v21sor1195764edb.5.2017.12.13.04.57.41 for (Google Transport Security); Wed, 13 Dec 2017 04:57:41 -0800 (PST) Date: Wed, 13 Dec 2017 15:57:40 +0300 From: "Kirill A. Shutemov" Subject: Re: [patch 05/16] mm: Allow special mappings with user access cleared Message-ID: <20171213125739.fllckbl3o4nonmpx@node.shutemov.name> References: <20171212173221.496222173@linutronix.de> <20171212173333.669577588@linutronix.de> <20171213122211.bxcb7xjdwla2bqol@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171213122211.bxcb7xjdwla2bqol@hirez.programming.kicks-ass.net> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra , Dave Hansen Cc: Andy Lutomirski , Thomas Gleixner , LKML , X86 ML , Linus Torvalds , Borislav Petkov , Greg KH , Kees Cook , Hugh Dickins , Brian Gerst , Josh Poimboeuf , Denys Vlasenko , Boris Ostrovsky , Juergen Gross , David Laight , Eduardo Valentin , aliguori@amazon.com, Will Deacon , "linux-mm@kvack.org" , kirill.shutemov@linux.intel.com, aneesh.kumar@linux.vnet.ibm.com On Wed, Dec 13, 2017 at 01:22:11PM +0100, Peter Zijlstra wrote: > On Tue, Dec 12, 2017 at 10:00:08AM -0800, Andy Lutomirski wrote: > > On Tue, Dec 12, 2017 at 9:32 AM, Thomas Gleixner wrote: > > > From: Peter Zijstra > > > > > > In order to create VMAs that are not accessible to userspace create a new > > > VM_NOUSER flag. This can be used in conjunction with > > > install_special_mapping() to inject 'kernel' data into the userspace map. > > > > > > Similar to how arch_vm_get_page_prot() allows adding _PAGE_flags to > > > pgprot_t, introduce arch_vm_get_page_prot_excl() which masks > > > _PAGE_flags from pgprot_t and use this to implement VM_NOUSER for x86. > > > > How does this interact with get_user_pages(), etc? > > So I went through that code and I think I found a bug related to this. > > get_user_pages_fast() will ultimately end up doing > pte_access_permitted() before getting the page, follow_page OTOH does > not do this, which makes for a curious difference between the two. > > So I'm thinking we want the below irrespective of the VM_NOUSER patch, > but with VM_NOUSER it would mean write(2) will no longer be able to > access the page. Oh.. We do call pte_access_permitted(), but only for write access. See can_follow_write_pte(). The issue seems bigger: we also need such calls for other page table levels :-/ Dave, what is effect of this on protection keys? > > diff --git a/mm/gup.c b/mm/gup.c > index dfcde13f289a..b852f37a2b0c 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -153,6 +153,11 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, > } > > if (flags & FOLL_GET) { > + if (!pte_access_permitted(pte, !!(flags & FOLL_WRITE))) { > + page = ERR_PTR(-EFAULT); > + goto out; > + } > + > get_page(page); > > /* drop the pgmap reference now that we hold the page */ > > > > -- > 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 -- Kirill A. Shutemov -- 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