Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756464AbbKRRY3 (ORCPT ); Wed, 18 Nov 2015 12:24:29 -0500 Received: from foss.arm.com ([217.140.101.70]:36193 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753108AbbKRRY2 (ORCPT ); Wed, 18 Nov 2015 12:24:28 -0500 Date: Wed, 18 Nov 2015 17:24:23 +0000 From: Catalin Marinas To: Andrey Ryabinin Cc: linux-arm-kernel@lists.infradead.org, Yury , Arnd Bergmann , Ard Biesheuvel , Andrey Konovalov , Linus Walleij , "Suzuki K. Poulose" , Will Deacon , linux-kernel@vger.kernel.org, kasan-dev , linux-mm@kvack.org, Alexander Potapenko , Alexey Klimov , David Keitel , Dmitry Vyukov Subject: Re: [PATCH v7 0/4] KASAN for arm64 Message-ID: <20151118172422.GA5799@e104818-lin.cambridge.arm.com> References: <1444665180-301-1-git-send-email-ryabinin.a.a@gmail.com> <20151013083432.GG6320@e104818-lin.cambridge.arm.com> <5649BAFD.6030005@arm.com> <5649F783.40109@gmail.com> <20151116165100.GE6556@e104818-lin.cambridge.arm.com> <564C8C47.1080904@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <564C8C47.1080904@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2066 Lines: 48 On Wed, Nov 18, 2015 at 05:33:43PM +0300, Andrey Ryabinin wrote: > On 11/16/2015 07:51 PM, Catalin Marinas wrote: > > On Mon, Nov 16, 2015 at 06:34:27PM +0300, Andrey Ryabinin wrote: > >> On 11/16/2015 02:16 PM, Suzuki K. Poulose wrote: > >>> arch/arm64/mm/kasan_init.c:95:2: note: in expansion of macro ‘BUILD_BUG_ON’ > >>> BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE)); > >>> > >>> The problem is that the PGDIR_SIZE is (1UL << 47) with 16K+48bit, which makes > >>> the KASAN_SHADOW_END unaligned(which is aligned to (1UL << (48 - 3)) ). Is the > >>> alignment really needed ? Thoughts on how best we could fix this ? > >> > >> Yes, it's really needed, because some code relies on this (e.g. > >> clear_pgs() and kasan_init()). But it should be possible to get rid of > >> this requirement. > > > > I don't think clear_pgds() and kasan_init() are the only problems. IIUC, > > kasan_populate_zero_shadow() also assumes that KASan shadow covers > > multiple pgds. You need some kind of recursive writing which avoids > > populating an entry which is not empty (like kasan_early_pud_populate). > > I think kasan_populate_zero_shadow() should be fine. We call pgd_populate() only > if address range covers the entire pgd: > > if (IS_ALIGNED(addr, PGDIR_SIZE) && end - addr >= PGDIR_SIZE) { > .... > pgd_populate(&init_mm, pgd, kasan_zero_pud); > .... > > and otherwise we check for pgd_none(*pgd): > if (pgd_none(*pgd)) { > pgd_populate(&init_mm, pgd, > early_alloc(PAGE_SIZE, NUMA_NO_NODE)); > } OK, I missed the fact that zero_pud_populate() handles the pmd/pte population with kasan_zero_*. So if it's only tmp_pg_dir, as you said already, you can add a tmp_pud for the case where KASAN_SHADOW_SIZE is smaller than PGDIR_SIZE and change clear_pgds() to erase the puds. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/