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=-11.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 0840FC2D0A8 for ; Wed, 30 Sep 2020 08:03:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A99AB2074A for ; Wed, 30 Sep 2020 08:03:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728508AbgI3IDW (ORCPT ); Wed, 30 Sep 2020 04:03:22 -0400 Received: from foss.arm.com ([217.140.110.172]:59048 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728480AbgI3IDW (ORCPT ); Wed, 30 Sep 2020 04:03:22 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2D1F0D6E; Wed, 30 Sep 2020 01:03:21 -0700 (PDT) Received: from [10.163.73.166] (unknown [10.163.73.166]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 447ED3F6CF; Wed, 30 Sep 2020 01:03:17 -0700 (PDT) From: Anshuman Khandual Subject: Re: [PATCH] arm64/mm: Validate hotplug range before creating linear mapping To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, Mark Rutland , Ard Biesheuvel , Steven Price , Robin Murphy , David Hildenbrand , Andrew Morton , linux-kernel@vger.kernel.org References: <1600332402-30123-1-git-send-email-anshuman.khandual@arm.com> <20200928203539.GA12218@willie-the-truck> <09266aed-7eef-5b16-5d52-0dcb7dcb7246@arm.com> <20200929152221.GA13995@willie-the-truck> Message-ID: Date: Wed, 30 Sep 2020 13:32:16 +0530 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: <20200929152221.GA13995@willie-the-truck> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/29/2020 08:52 PM, Will Deacon wrote: > On Tue, Sep 29, 2020 at 01:34:24PM +0530, Anshuman Khandual wrote: >> >> >> On 09/29/2020 02:05 AM, Will Deacon wrote: >>> On Thu, Sep 17, 2020 at 02:16:42PM +0530, Anshuman Khandual wrote: >>>> During memory hotplug process, the linear mapping should not be created for >>>> a given memory range if that would fall outside the maximum allowed linear >>>> range. Else it might cause memory corruption in the kernel virtual space. >>>> >>>> Maximum linear mapping region is [PAGE_OFFSET..(PAGE_END -1)] accommodating >>>> both its ends but excluding PAGE_END. Max physical range that can be mapped >>>> inside this linear mapping range, must also be derived from its end points. >>>> >>>> When CONFIG_ARM64_VA_BITS_52 is enabled, PAGE_OFFSET is computed with the >>>> assumption of 52 bits virtual address space. However, if the CPU does not >>>> support 52 bits, then it falls back using 48 bits instead and the PAGE_END >>>> is updated to reflect this using the vabits_actual. As for PAGE_OFFSET, >>>> bits [51..48] are ignored by the MMU and remain unchanged, even though the >>>> effective start address of linear map is now slightly different. Hence, to >>>> reliably check the physical address range mapped by the linear map, the >>>> start address should be calculated using vabits_actual. This ensures that >>>> arch_add_memory() validates memory hot add range for its potential linear >>>> mapping requirement, before creating it with __create_pgd_mapping(). >>>> >>>> Cc: Catalin Marinas >>>> Cc: Will Deacon >>>> Cc: Mark Rutland >>>> Cc: Ard Biesheuvel >>>> Cc: Steven Price >>>> Cc: Robin Murphy >>>> Cc: David Hildenbrand >>>> Cc: Andrew Morton >>>> Cc: linux-arm-kernel@lists.infradead.org >>>> Cc: linux-kernel@vger.kernel.org >>>> Fixes: 4ab215061554 ("arm64: Add memory hotplug support") >>>> Signed-off-by: Anshuman Khandual >>>> --- >>>> arch/arm64/mm/mmu.c | 27 +++++++++++++++++++++++++++ >>>> 1 file changed, 27 insertions(+) >>>> >>>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >>>> index 75df62fea1b6..d59ffabb9c84 100644 >>>> --- a/arch/arm64/mm/mmu.c >>>> +++ b/arch/arm64/mm/mmu.c >>>> @@ -1433,11 +1433,38 @@ static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size) >>>> free_empty_tables(start, end, PAGE_OFFSET, PAGE_END); >>>> } >>>> >>>> +static bool inside_linear_region(u64 start, u64 size) >>>> +{ >>>> + /* >>>> + * Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)] >>>> + * accommodating both its ends but excluding PAGE_END. Max physical >>>> + * range which can be mapped inside this linear mapping range, must >>>> + * also be derived from its end points. >>>> + * >>>> + * With CONFIG_ARM64_VA_BITS_52 enabled, PAGE_OFFSET is defined with >>>> + * the assumption of 52 bits virtual address space. However, if the >>>> + * CPU does not support 52 bits, it falls back using 48 bits and the >>>> + * PAGE_END is updated to reflect this using the vabits_actual. As >>>> + * for PAGE_OFFSET, bits [51..48] are ignored by the MMU and remain >>>> + * unchanged, even though the effective start address of linear map >>>> + * is now slightly different. Hence, to reliably check the physical >>>> + * address range mapped by the linear map, the start address should >>>> + * be calculated using vabits_actual. >>>> + */ >>>> + return ((start >= __pa(_PAGE_OFFSET(vabits_actual))) >>>> + && ((start + size) <= __pa(PAGE_END - 1))); >>>> +} >>> >>> Why isn't this implemented using the existing __is_lm_address()? >> >> Not sure, if I understood your suggestion here. The physical address range >> [start..start + size] needs to be checked against maximum physical range >> that can be represented inside effective boundaries for the linear mapping >> i.e [__pa(_PAGE_OFFSET(vabits_actual)..__pa(PAGE_END - 1)]. >> >> Are you suggesting [start..start + size] should be first be converted into >> a virtual address range and then checked against __is_lm_addresses() ? But >> is not deriving the physical range from from know limits of linear mapping >> much cleaner ? > > I just think having a function called "inside_linear_region()" as well as a > macro called "__is_lm_address()" is weird when they have completely separate > implementations. They're obviously trying to do the same thing, just the > first one gets given physical address as parameters. > > Implementing one in terms of the other is much better for maintenance. /* * The linear kernel range starts at the bottom of the virtual address * space. Testing the top bit for the start of the region is a * sufficient check and avoids having to worry about the tag. */ #define __is_lm_address(addr) (!(((u64)addr) & BIT(vabits_actual - 1))) __is_lm_address() currently just check the highest bit in a virtual address where the linear mapping ends i.e the lower half and all other kernel mapping starts i.e the upper half. But I would believe, it misses the blind range [_PAGE_OFFSET(VA_BITS).._PAGE_OFFSET(vabits_actual)] in some configurations, even though it does not really affect anything because it gets ignored by the MMU. Hence in current form __is_lm_address() cannot be used to derive maximum linear range and it's corresponding physical range for hotplug range check. But if __is_lm_address() checks against the effective linear range instead i.e [_PAGE_OFFSET(vabits_actual)..(PAGE_END - 1)], it can be used for hot plug physical range check there after. Perhaps something like this, though not tested properly. diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h index afa722504bfd..6da046b479d4 100644 --- a/arch/arm64/include/asm/memory.h +++ b/arch/arm64/include/asm/memory.h @@ -238,7 +238,10 @@ static inline const void *__tag_set(const void *addr, u8 tag) * space. Testing the top bit for the start of the region is a * sufficient check and avoids having to worry about the tag. */ -#define __is_lm_address(addr) (!(((u64)addr) & BIT(vabits_actual - 1))) +static inline bool __is_lm_address(unsigned long addr) +{ + return ((addr >= _PAGE_OFFSET(vabits_actual)) && (addr <= (PAGE_END - 1))); +} #define __lm_to_phys(addr) (((addr) + physvirt_offset)) #define __kimg_to_phys(addr) ((addr) - kimage_voffset) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index d59ffabb9c84..5750370a7e8c 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -1451,8 +1451,7 @@ static bool inside_linear_region(u64 start, u64 size) * address range mapped by the linear map, the start address should * be calculated using vabits_actual. */ - return ((start >= __pa(_PAGE_OFFSET(vabits_actual))) - && ((start + size) <= __pa(PAGE_END - 1))); + return __is_lm_address(__va(start)) && __is_lm_address(__va(start + size)); } int arch_add_memory(int nid, u64 start, u64 size,