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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 F1480C433DF for ; Tue, 23 Jun 2020 09:57:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CD2C320738 for ; Tue, 23 Jun 2020 09:57:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592906263; bh=I6FXAd+dz0PTFAbZZ7Ggg1D9VAM+5cmaOuIX+WynUXY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=L5ZZQpMHf+BdjWq/9wYcnoxfnBqSE9PVMkgQFobbKdzROgLC5wHFg2GZjbEqy6HFD 6/rH/LJfXdoNPmQSt3BfEUzf8oXJ14NFEzg97LKi8YLrjCBA9zleTEmiuSin1iFwVd wnfc0P8x6BqMVtpDL0WpojD3MVG9wXtUq4IV3Pxc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732100AbgFWJ5n (ORCPT ); Tue, 23 Jun 2020 05:57:43 -0400 Received: from mail.kernel.org ([198.145.29.99]:35592 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731947AbgFWJ5n (ORCPT ); Tue, 23 Jun 2020 05:57:43 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2380020771; Tue, 23 Jun 2020 09:57:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592906263; bh=I6FXAd+dz0PTFAbZZ7Ggg1D9VAM+5cmaOuIX+WynUXY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=EkrUXXkMa7i2f43LSN2xaCpKDWrWjr9vOWsyZcdZfiB4wnJ0kZuDW76qe4YyJNbrA aEg23Q87gKOMdnDv8U0QvRrDTW7qWtqkVsfHY073/OprQW1G+a9vHKzgntu2AxnTod 889AuqDXeVGDQuPIkRG0Lyv7qEbtZ0eDRJML51+w= Date: Tue, 23 Jun 2020 10:57:38 +0100 From: Will Deacon To: Peter Zijlstra Cc: Christoph Hellwig , Andrew Morton , Dexuan Cui , Vitaly Kuznetsov , Catalin Marinas , Jessica Yu , x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 2/3] arm64: use PAGE_KERNEL_ROX directly in alloc_insn_page Message-ID: <20200623095737.GD3743@willie-the-truck> References: <20200618064307.32739-1-hch@lst.de> <20200618064307.32739-3-hch@lst.de> <20200620191616.bae356186ba3329ade67bbf7@linux-foundation.org> <20200623090505.GA7518@lst.de> <20200623090757.GB3743@willie-the-truck> <20200623093714.GE4781@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200623093714.GE4781@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On Tue, Jun 23, 2020 at 11:37:14AM +0200, Peter Zijlstra wrote: > On Tue, Jun 23, 2020 at 10:07:58AM +0100, Will Deacon wrote: > > On Tue, Jun 23, 2020 at 11:05:05AM +0200, Christoph Hellwig wrote: > > > On Sat, Jun 20, 2020 at 07:16:16PM -0700, Andrew Morton wrote: > > > > On Thu, 18 Jun 2020 08:43:06 +0200 Christoph Hellwig wrote: > > > > > --- a/arch/arm64/kernel/probes/kprobes.c > > > > > +++ b/arch/arm64/kernel/probes/kprobes.c > > > > > @@ -120,15 +120,9 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p) > > > > > > > > > > void *alloc_insn_page(void) > > > > > { > > > > > - void *page; > > > > > - > > > > > - page = vmalloc_exec(PAGE_SIZE); > > > > > - if (page) { > > > > > - set_memory_ro((unsigned long)page, 1); > > > > > - set_vm_flush_reset_perms(page); > > > > > - } > > > > > - > > > > > - return page; > > > > > + return __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START, VMALLOC_END, > > > > > + GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS, > > > > > + NUMA_NO_NODE, __func__); > > > > > } > > > > > > > > > > /* arm kprobe: install breakpoint in text */ > > > > > > > > But why. I think this is just a cleanup, doesn't address any runtime issue? > > > > > > It doesn't "fix" an issue - it just simplifies and speeds up the code. > > > > Ok, but I don't understand the PLT comment from Peter in > > 20200618092754.GF576905@hirez.programming.kicks-ass.net: > > > > | I think this has the exact same range issue as the x86 user. But it > > | might be less fatal if their PLT magic can cover the full range. > > > > Peter, please could you elaborate on your concern? I feel like I'm missing > > some context. > > On x86 we can only directly call code in a (signed) 32bit immediate > range (2G) and our kernel text and module range are constrained by that. > > IIRC ARM64 has an even smaller immediate range and needs to play fixup > games with trampolines or somesuch (there was an ARM specific name for > it that I've misplaced again). Does that machinery cover the entire > vmalloc space or are you only able to fix up for a smaller range? > > Your arch/arm64/kernel/module.c:module_alloc() implementation seems to > have an explicit module range different from the full vmalloc range, I'm > thinking this is for a reason. Ah, gotcha. In this case, we're talking about the kprobe out-of-line buffer. We don't directly branch to that; instead we take a BRK exception and either exception return + singlestep the OOL buffer, or we simulate the instruction if it's doing anything PC-relative, so I don't see the need for a PLT. Will