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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 BE7E4C43143 for ; Mon, 1 Oct 2018 10:41:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 77E962064A for ; Mon, 1 Oct 2018 10:41:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 77E962064A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729026AbeJARSx (ORCPT ); Mon, 1 Oct 2018 13:18:53 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:46728 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728999AbeJARSw (ORCPT ); Mon, 1 Oct 2018 13:18:52 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id ADADC18A; Mon, 1 Oct 2018 03:41:42 -0700 (PDT) Received: from [10.4.12.81] (melchizedek.Emea.Arm.com [10.4.12.81]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3FB573F5B3; Mon, 1 Oct 2018 03:41:41 -0700 (PDT) Subject: Re: [PATCH v5 5/6] arm64/mm: Populate the swapper_pg_dir by fixmap. To: Mark Rutland , Jun Yao Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org References: <20180917044333.30051-1-yaojun8558363@gmail.com> <20180917044333.30051-6-yaojun8558363@gmail.com> <20180924163619.rx7bae67i5isq2fy@lakrids.cambridge.arm.com> From: James Morse Message-ID: <24c91d6c-85c8-afb4-74d1-202e4d780ab6@arm.com> Date: Mon, 1 Oct 2018 11:41:37 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180924163619.rx7bae67i5isq2fy@lakrids.cambridge.arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Mark, On 24/09/18 17:36, Mark Rutland wrote: > On Mon, Sep 17, 2018 at 12:43:32PM +0800, Jun Yao wrote: >> Since we will move the swapper_pg_dir to rodata section, we need a >> way to update it. The fixmap can handle it. When the swapper_pg_dir >> needs to be updated, we map it dynamically. The map will be >> canceled after the update is complete. In this way, we can defend >> against KSMA(Kernel Space Mirror Attack). >> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >> index 71532bcd76c1..a8a60927f716 100644 >> --- a/arch/arm64/mm/mmu.c >> +++ b/arch/arm64/mm/mmu.c >> @@ -67,6 +67,24 @@ static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss; >> static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss __maybe_unused; >> static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss __maybe_unused; >> >> +static DEFINE_SPINLOCK(swapper_pgdir_lock); >> + >> +void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd) >> +{ >> + pgd_t *fixmap_pgdp; >> + >> + spin_lock(&swapper_pgdir_lock); >> + fixmap_pgdp = pgd_set_fixmap(__pa(pgdp)); >> + WRITE_ONCE(*fixmap_pgdp, pgd); >> + /* >> + * We need dsb(ishst) here to ensure the page-table-walker sees >> + * our new entry before set_p?d() returns. The fixmap's >> + * flush_tlb_kernel_range() via clear_fixmap() does this for us. >> + */ >> + pgd_clear_fixmap(); >> + spin_unlock(&swapper_pgdir_lock); >> +} > > I'm rather worried that we could deadlock here. We can use the irqsave versions if you're worried, but I think any code doing this is already broken. (I'd like to eventually depend on the init_mm.page_table_lock for this, but it isn't held when the vmemmap is being populated.) > Are we certain we never poke the kernel page tables in IRQ context? The RAS code was doing this, but was deemed unsafe, and changed to use the fixmap: https://lkml.org/lkml/2017/10/30/500 The fixmap only ever touches the last level, so can't hit this. x86 can't do its IPI tlb-maintenance from IRQ context, so anything trying to unmap from irq context is already broken: https://lkml.org/lkml/2018/9/6/324 vunmap()/vfree() is allowed from irq context, but it defers its work. I can't find any way to pass GFP_ATOMIC into ioremap(), I didn't think vmalloc() could either, ... but now I spot __vmalloc() does... This __vmalloc() path is used by the percpu allocator, which starting from pcpu_alloc() can be passed something other than GFP_KERNEL, and uses spin_lock_irqsave(), so it is expecting to be called in irq context. ... so yes it looks like this can happen. I'll post a fix Thanks! James