From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1D226C433DF for ; Tue, 16 Jun 2020 10:23:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F3078207BC for ; Tue, 16 Jun 2020 10:23:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728314AbgFPKXz (ORCPT ); Tue, 16 Jun 2020 06:23:55 -0400 Received: from verein.lst.de ([213.95.11.211]:37428 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728258AbgFPKXx (ORCPT ); Tue, 16 Jun 2020 06:23:53 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 9A3B568AEF; Tue, 16 Jun 2020 12:23:50 +0200 (CEST) Date: Tue, 16 Jun 2020 12:23:50 +0200 From: Christoph Hellwig To: Peter Zijlstra Cc: Christoph Hellwig , Dexuan Cui , vkuznets , Stephen Hemminger , Andy Lutomirski , Andy Lutomirski , Michael Kelley , Ju-Hyoung Lee , "x86@kernel.org" , "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" , KY Srinivasan , Tom Lendacky Subject: Re: hv_hypercall_pg page permissios Message-ID: <20200616102350.GA29684@lst.de> References: <20200407073830.GA29279@lst.de> <87y2ooiv5k.fsf@vitty.brq.redhat.com> <20200616072318.GA17600@lst.de> <20200616101807.GO2531@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200616101807.GO2531@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On Tue, Jun 16, 2020 at 12:18:07PM +0200, Peter Zijlstra wrote: > > It does. But it also means every other user of PAGE_KERNEL_EXEC > > should trigger this, of which there are a few (kexec, tboot, hibernate, > > early xen pv mapping, early SEV identity mapping) > > There are only 3 users in the entire tree afaict: > > arch/arm64/kernel/probes/kprobes.c: page = vmalloc_exec(PAGE_SIZE); > arch/x86/hyperv/hv_init.c: hv_hypercall_pg = vmalloc_exec(PAGE_SIZE); > kernel/module.c: return vmalloc_exec(size); > > And that last one is a weak function that any arch that has STRICT_RWX > ought to override. > > > We really shouldn't create mappings like this by default. Either we > > need to flip PAGE_KERNEL_EXEC itself based on the needs of the above > > users, or add another define to overload vmalloc_exec as there is no > > other user of that for x86. > > We really should get rid of the two !module users of this though; both > x86 and arm64 have STRICT_RWX and sufficient primitives to DTRT. > > What is HV even trying to do with that page? AFAICT it never actually > writes to it, it seens to give the physica address to an MSR (which I > suspect then writes crud into the page for us from host context). > > Suggesting the page really only needs to be RX. > > On top of that, vmalloc_exec() gets us a page from the entire vmalloc > range, which can be outside of the 2G executable range, which seems to > suggest vmalloc_exec() is wrong too and all this works by accident. > > How about something like this: > > > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c > index a54c6a401581..82a3a4a9481f 100644 > --- a/arch/x86/hyperv/hv_init.c > +++ b/arch/x86/hyperv/hv_init.c > @@ -375,12 +375,15 @@ void __init hyperv_init(void) > guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0); > wrmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id); > > - hv_hypercall_pg = vmalloc_exec(PAGE_SIZE); > + hv_hypercall_pg = module_alloc(PAGE_SIZE); > if (hv_hypercall_pg == NULL) { > wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0); > goto remove_cpuhp_state; > } > > + set_memory_ro((unsigned long)hv_hypercall_pg, 1); > + set_memory_x((unsigned long)hv_hypercall_pg, 1); The changing of the permissions sucks. I thought about adding a module_alloc_prot with an explicit pgprot_t argument. On x86 alone at least ftrace would also benefit from that.