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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 6A5C3C169C4 for ; Mon, 11 Feb 2019 16:28:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3A9F9218F0 for ; Mon, 11 Feb 2019 16:28:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728451AbfBKQ2R (ORCPT ); Mon, 11 Feb 2019 11:28:17 -0500 Received: from relay.sw.ru ([185.231.240.75]:52414 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727144AbfBKQ2R (ORCPT ); Mon, 11 Feb 2019 11:28:17 -0500 Received: from [172.16.25.12] by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1gtERF-0001Xi-Kx; Mon, 11 Feb 2019 19:28:09 +0300 Subject: Re: [PATCH v4 3/3] powerpc/32: Add KASAN support To: Andrey Konovalov , christophe leroy Cc: Daniel Axtens , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Nicholas Piggin , "Aneesh Kumar K.V" , Alexander Potapenko , Dmitry Vyukov , Linux Memory Management List , PowerPC , LKML , kasan-dev References: <1f5629e03181d0e30efc603f00dad78912991a45.1548166824.git.christophe.leroy@c-s.fr> <87ef8i45km.fsf@dja-thinkpad.axtens.net> <69720148-fd19-0810-5a1d-96c45e2ec00c@c-s.fr> From: Andrey Ryabinin Message-ID: <805fbf9d-a10f-03e0-aa52-6f6bd16059b9@virtuozzo.com> Date: Mon, 11 Feb 2019 19:28:31 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/11/19 3:25 PM, Andrey Konovalov wrote: > On Sat, Feb 9, 2019 at 12:55 PM christophe leroy > wrote: >> >> Hi Andrey, >> >> Le 08/02/2019 à 18:40, Andrey Konovalov a écrit : >>> On Fri, Feb 8, 2019 at 6:17 PM Christophe Leroy wrote: >>>> >>>> Hi Daniel, >>>> >>>> Le 08/02/2019 à 17:18, Daniel Axtens a écrit : >>>>> Hi Christophe, >>>>> >>>>> I've been attempting to port this to 64-bit Book3e nohash (e6500), >>>>> although I think I've ended up with an approach more similar to Aneesh's >>>>> much earlier (2015) series for book3s. >>>>> >>>>> Part of this is just due to the changes between 32 and 64 bits - we need >>>>> to hack around the discontiguous mappings - but one thing that I'm >>>>> particularly puzzled by is what the kasan_early_init is supposed to do. >>>> >>>> It should be a problem as my patch uses a 'for_each_memblock(memory, >>>> reg)' loop. >>>> >>>>> >>>>>> +void __init kasan_early_init(void) >>>>>> +{ >>>>>> + unsigned long addr = KASAN_SHADOW_START; >>>>>> + unsigned long end = KASAN_SHADOW_END; >>>>>> + unsigned long next; >>>>>> + pmd_t *pmd = pmd_offset(pud_offset(pgd_offset_k(addr), addr), addr); >>>>>> + int i; >>>>>> + phys_addr_t pa = __pa(kasan_early_shadow_page); >>>>>> + >>>>>> + BUILD_BUG_ON(KASAN_SHADOW_START & ~PGDIR_MASK); >>>>>> + >>>>>> + if (early_mmu_has_feature(MMU_FTR_HPTE_TABLE)) >>>>>> + panic("KASAN not supported with Hash MMU\n"); >>>>>> + >>>>>> + for (i = 0; i < PTRS_PER_PTE; i++) >>>>>> + __set_pte_at(&init_mm, (unsigned long)kasan_early_shadow_page, >>>>>> + kasan_early_shadow_pte + i, >>>>>> + pfn_pte(PHYS_PFN(pa), PAGE_KERNEL_RO), 0); >>>>>> + >>>>>> + do { >>>>>> + next = pgd_addr_end(addr, end); >>>>>> + pmd_populate_kernel(&init_mm, pmd, kasan_early_shadow_pte); >>>>>> + } while (pmd++, addr = next, addr != end); >>>>>> +} >>>>> >>>>> As far as I can tell it's mapping the early shadow page, read-only, over >>>>> the KASAN_SHADOW_START->KASAN_SHADOW_END range, and it's using the early >>>>> shadow PTE array from the generic code. >>>>> >>>>> I haven't been able to find an answer to why this is in the docs, so I >>>>> was wondering if you or anyone else could explain the early part of >>>>> kasan init a bit better. >>>> >>>> See https://www.kernel.org/doc/html/latest/dev-tools/kasan.html for an >>>> explanation of the shadow. >>>> >>>> When shadow is 0, it means the memory area is entirely accessible. >>>> >>>> It is necessary to setup a shadow area as soon as possible because all >>>> data accesses check the shadow area, from the begining (except for a few >>>> files where sanitizing has been disabled in Makefiles). >>>> >>>> Until the real shadow area is set, all access are granted thanks to the >>>> zero shadow area beeing for of zeros. >>> >>> Not entirely correct. kasan_early_init() indeed maps the whole shadow >>> memory range to the same kasan_early_shadow_page. However as kernel >>> loads and memory gets allocated this shadow page gets rewritten with >>> non-zero values by different KASAN allocator hooks. Since these values >>> come from completely different parts of the kernel, but all land on >>> the same page, kasan_early_shadow_page's content can be considered >>> garbage. When KASAN checks memory accesses for validity it detects >>> these garbage shadow values, but doesn't print any reports, as the >>> reporting routine bails out on the current->kasan_depth check (which >>> has the value of 1 initially). Only after kasan_init() completes, when >>> the proper shadow memory is mapped, current->kasan_depth gets set to 0 >>> and we start reporting bad accesses. >> >> That's surprising, because in the early phase I map the shadow area >> read-only, so I do not expect it to get modified unless RO protection is >> failing for some reason. > > Actually it might be that the allocator hooks don't modify shadow at > this point, as the allocator is not yet initialized. However stack > should be getting poisoned and unpoisoned from the very start. But the > generic statement that early shadow gets dirtied should be correct. > Might it be that you don't use stack instrumentation? > Yes, stack instrumentation is not used here, because shadow offset which we pass to the -fasan-shadow-offset= cflag is not specified here. So the logic in scrpits/Makefile.kasan just fallbacks to CFLAGS_KASAN_MINIMAL, which is outline and without stack instrumentation. Christophe, you can specify KASAN_SHADOW_OFFSET either in Kconfig (e.g. x86_64) or in Makefile (e.g. arm64). And make early mapping writable, because compiler generated code will write to shadow memory in function prologue/epilogue.