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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 0A05DC433E0 for ; Thu, 21 Jan 2021 15:14:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BC51C239D4 for ; Thu, 21 Jan 2021 15:14:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732439AbhAUPOQ (ORCPT ); Thu, 21 Jan 2021 10:14:16 -0500 Received: from foss.arm.com ([217.140.110.172]:39004 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732166AbhAUPM5 (ORCPT ); Thu, 21 Jan 2021 10:12:57 -0500 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 F2C9A139F; Thu, 21 Jan 2021 07:12:11 -0800 (PST) Received: from C02TD0UTHF1T.local (unknown [10.57.35.62]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 34E4A3F68F; Thu, 21 Jan 2021 07:12:09 -0800 (PST) Date: Thu, 21 Jan 2021 15:12:06 +0000 From: Mark Rutland To: Vincenzo Frascino Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, Andrey Konovalov , Leon Romanovsky , Alexander Potapenko , Catalin Marinas , Andrey Ryabinin , Will Deacon , Dmitry Vyukov , Ard Biesheuvel Subject: Re: [PATCH v2 1/2] arm64: Fix kernel address detection of __is_lm_address() Message-ID: <20210121151206.GI48431@C02TD0UTHF1T.local> References: <20210121131956.23246-1-vincenzo.frascino@arm.com> <20210121131956.23246-2-vincenzo.frascino@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210121131956.23246-2-vincenzo.frascino@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [adding Ard] On Thu, Jan 21, 2021 at 01:19:55PM +0000, Vincenzo Frascino wrote: > Currently, the __is_lm_address() check just masks out the top 12 bits > of the address, but if they are 0, it still yields a true result. > This has as a side effect that virt_addr_valid() returns true even for > invalid virtual addresses (e.g. 0x0). When it was added, __is_lm_address() was intended to distinguish valid kernel virtual addresses (i.e. those in the TTBR1 address range), and wasn't intended to do anything for addresses outside of this range. See commit: ec6d06efb0bac6cd ("arm64: Add support for CONFIG_DEBUG_VIRTUAL") ... where it simply tests a bit. So I believe that it's working as intended (though this is poorly documented), but I think you're saying that usage isn't aligned with that intent. Given that, I'm not sure the fixes tag is right; I think it has never had the semantic you're after. I had thought the same was true for virt_addr_valid(), and that wasn't expected to be called for VAs outside of the kernel VA range. Is it actually safe to call that with NULL on other architectures? I wonder if it's worth virt_addr_valid() having an explicit check for the kernel VA range, instead. > Fix the detection checking that it's actually a kernel address starting > at PAGE_OFFSET. > > Fixes: f4693c2716b35 ("arm64: mm: extend linear region for 52-bit VA configurations") > Cc: Catalin Marinas > Cc: Will Deacon > Suggested-by: Catalin Marinas > Signed-off-by: Vincenzo Frascino > --- > arch/arm64/include/asm/memory.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h > index 18fce223b67b..e04ac898ffe4 100644 > --- a/arch/arm64/include/asm/memory.h > +++ b/arch/arm64/include/asm/memory.h > @@ -249,7 +249,7 @@ static inline const void *__tag_set(const void *addr, u8 tag) > /* > * The linear kernel range starts at the bottom of the virtual address space. > */ > -#define __is_lm_address(addr) (((u64)(addr) & ~PAGE_OFFSET) < (PAGE_END - PAGE_OFFSET)) > +#define __is_lm_address(addr) (((u64)(addr) ^ PAGE_OFFSET) < (PAGE_END - PAGE_OFFSET)) If we're going to make this stronger, can we please expand the comment with the intended semantic? Otherwise we're liable to break this in future. Thanks, Mark.