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 04CCCC43143 for ; Mon, 1 Oct 2018 13:49:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C9FDD208AE for ; Mon, 1 Oct 2018 13:49:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C9FDD208AE 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 S1729406AbeJAU1B (ORCPT ); Mon, 1 Oct 2018 16:27:01 -0400 Received: from foss.arm.com ([217.140.101.70]:49372 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729298AbeJAU1B (ORCPT ); Mon, 1 Oct 2018 16:27:01 -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 364447A9; Mon, 1 Oct 2018 06:49:07 -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 BA1F93F5B7; Mon, 1 Oct 2018 06:49:05 -0700 (PDT) Subject: Re: [PATCH v5 5/6] arm64/mm: Populate the swapper_pg_dir by fixmap. From: James Morse 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> <24c91d6c-85c8-afb4-74d1-202e4d780ab6@arm.com> Message-ID: <5a8ee1d0-67c6-b8ff-562d-ad9fe4ac0423@arm.com> Date: Mon, 1 Oct 2018 14:49:04 +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: <24c91d6c-85c8-afb4-74d1-202e4d780ab6@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 01/10/18 11:41, James Morse wrote: > 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); >>> +} >> 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. But! These two things (irq-context and calls-__vmalloc()) can't happen at the same time. If pcpu_alloc() is passed GFP_ATOMIC, and pcpu_alloc_area() fails, (so a new chunk needs to be allocated), it will fail instead. (This explains the scary looking "if (!in_atomic) mutex_lock()", in that code). If you try it, you hit the "BUG_ON(in_interrupt())", in __get_vm_area_node(). So even if you do pass GFP_ATOMIC in here, you can't call it from interrupt context. (sanity prevails!) I was wrong, it doesn't need fixing. James