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=-8.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 87198C4363D for ; Fri, 25 Sep 2020 12:51:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5BE9B206DB for ; Fri, 25 Sep 2020 12:51:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729161AbgIYMvJ (ORCPT ); Fri, 25 Sep 2020 08:51:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:55176 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729145AbgIYMvE (ORCPT ); Fri, 25 Sep 2020 08:51:04 -0400 Received: from gaia (unknown [31.124.44.166]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 049DF22B2D; Fri, 25 Sep 2020 12:51:01 +0000 (UTC) Date: Fri, 25 Sep 2020 13:50:59 +0100 From: Catalin Marinas To: Vincenzo Frascino Cc: Andrey Konovalov , Dmitry Vyukov , kasan-dev@googlegroups.com, Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Elena Petrova , Branislav Rankov , Kevin Brodsky , Will Deacon , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 24/39] arm64: mte: Add in-kernel MTE helpers Message-ID: <20200925125059.GM4846@gaia> References: <20200925101558.GB4846@gaia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 25, 2020 at 12:28:24PM +0100, Vincenzo Frascino wrote: > On 9/25/20 11:15 AM, Catalin Marinas wrote: > > On Fri, Sep 25, 2020 at 12:50:31AM +0200, Andrey Konovalov wrote: > >> +u8 mte_get_mem_tag(void *addr); > >> +u8 mte_get_random_tag(void); > >> +void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag); > >> + > >> +#else /* CONFIG_ARM64_MTE */ > >> + > >> +static inline u8 mte_get_ptr_tag(void *ptr) > >> +{ > >> + return 0xFF; > >> +} > >> + > >> +static inline u8 mte_get_mem_tag(void *addr) > >> +{ > >> + return 0xFF; > >> +} > >> +static inline u8 mte_get_random_tag(void) > >> +{ > >> + return 0xFF; > >> +} > >> +static inline void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag) > >> +{ > >> + return addr; > >> +} > > > > Maybe these can stay in mte-kasan.h, although they are not a direct > > interface for KASAN AFAICT (the arch_* equivalent are defined in > > asm/memory.h. If there's no good reason, we could move them to mte.h. > > This is here because it is not a direct interface as you noticed. I tried to > keep the separation (even if it I have something to fix based on your comment > below ;)). > > The other kasan implementation define the arch_* indirection in asm/memory.h in > every architecture. I think maintaining the design is the best way to non create > confusion. I'm ok with asm/memory.h for kasan, no need to change that. You can also keep these functions in asm/mte-kasan.h but add a comment that they are only for the kasan interface defined in asm/memory.h. > >> diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h > >> index 1c99fcadb58c..3a2bf3ccb26c 100644 > >> --- a/arch/arm64/include/asm/mte.h > >> +++ b/arch/arm64/include/asm/mte.h > >> @@ -5,14 +5,13 @@ > >> #ifndef __ASM_MTE_H > >> #define __ASM_MTE_H > >> > >> -#define MTE_GRANULE_SIZE UL(16) > >> -#define MTE_GRANULE_MASK (~(MTE_GRANULE_SIZE - 1)) > >> -#define MTE_TAG_SHIFT 56 > >> -#define MTE_TAG_SIZE 4 > >> +#include And this include should be replaced by asm/mte-hwdef.h. > >> #ifndef __ASSEMBLY__ > >> > >> +#include > >> #include > >> +#include > >> > >> #include > >> > >> @@ -45,7 +44,9 @@ long get_mte_ctrl(struct task_struct *task); > >> int mte_ptrace_copy_tags(struct task_struct *child, long request, > >> unsigned long addr, unsigned long data); > >> > >> -#else > >> +void mte_assign_mem_tag_range(void *addr, size_t size); > > > > So mte_set_mem_tag_range() is KASAN specific but > > mte_assign_mem_tag_range() is not. Slightly confusing. > > mte_assign_mem_tag_range() is the internal function implemented in assembler > which is not used directly by KASAN. Is it the name that you find confusing? Do > you have a better proposal? I don't mind the name, just trying to find some consistency in the headers. > >> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > >> index 52a0638ed967..833b63fdd5e2 100644 > >> --- a/arch/arm64/kernel/mte.c > >> +++ b/arch/arm64/kernel/mte.c > >> @@ -13,8 +13,10 @@ > >> #include > >> #include > >> #include > >> +#include > >> #include > >> > >> +#include > >> #include > >> #include > >> #include > >> @@ -72,6 +74,48 @@ int memcmp_pages(struct page *page1, struct page *page2) > >> return ret; > >> } > >> > >> +u8 mte_get_mem_tag(void *addr) > >> +{ > >> + if (!system_supports_mte()) > >> + return 0xFF; > >> + > >> + asm volatile(__MTE_PREAMBLE "ldg %0, [%0]" > >> + : "+r" (addr)); [...] > > I wonder whether we'd need the "memory" clobber. I don't see how this > > would fail though, maybe later on with stack tagging if the compiler > > writes tags behind our back. > > > > As you said, I do not see how this can fail either. We can be overcautious > though here and add a comment that the clobber has been added in prevision of > stack tagging. I don't think we should bother, it may not even matter. > >> + */ > >> +SYM_FUNC_START(mte_assign_mem_tag_range) > >> + /* if (src == NULL) return; */ > >> + cbz x0, 2f > >> + /* if (size == 0) return; */ > >> + cbz x1, 2f > > > > I find these checks unnecessary, as I said a couple of times before, > > just document the function pre-conditions. They are also incomplete > > (i.e. you check for NULL but not alignment). > > > > I thought we agreed to harden the code further, based on [1]. Maybe I > misunderstood. I am going to remove them and extend the comment in the next version. > > [1] > https://lore.kernel.org/linux-arm-kernel/921c4ed0-b5b5-bc01-5418-c52d80f1af59@arm.com/ Well, you concluded that but I haven't confirmed ;). Since it's called from a single place which does the checks already, I don't see the point in duplicating them. Documenting should be sufficient. -- Catalin