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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DB3E2C38145 for ; Thu, 8 Sep 2022 13:50:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To: Subject:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=62ctCJVG+5oxwz/GDZg8NyPWSxf3D74mwxZLuhzn8Rc=; b=BXT9tmG+nFiv8J m8GIbBFwAnAeEL49DuF9JAAa8tOOMIj43f2elsx8sKJKZ51srmTzjFErVwppReAY+p3pCjraTN/e/ net2rlirHDWpIFS0rg4YjhZg7CS6ApvwDNxYolvyf4d5AqVeipGmkz5TGVnDgf7GBRvjYpt7dE5cg TOJcHjMSanN/0QhZwWDb0Xza+s317nbmd0JAz1q3kqD/rrJZHuIGBHhPr8lH2oBe+Xfv5cbzV2Afi GnUieiGTWapbCPB6LkMGw7pvbrJCZsD7gdkhWgENt1ufA8YyQuWjjR0vltrox7F6xbBV5s+ODGLdD Mm+9RtAtakuWP/oC26sQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oWHue-0047AM-3C; Thu, 08 Sep 2022 13:49:48 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oWHuW-00474Q-Hp for linux-arm-kernel@lists.infradead.org; Thu, 08 Sep 2022 13:49:46 +0000 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 6B4E423A; Thu, 8 Sep 2022 06:49:36 -0700 (PDT) Received: from [10.57.14.149] (unknown [10.57.14.149]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 72AF93F7B4; Thu, 8 Sep 2022 06:49:28 -0700 (PDT) Message-ID: <649ce069-050e-83c8-24d6-6aab6bb3f471@arm.com> Date: Thu, 8 Sep 2022 14:49:25 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v2] mte: Initialize tag storage to KASAN_TAG_INVALID Content-Language: en-US To: Vladimir Murzin , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com Cc: Catalin Marinas , Will Deacon References: <20220907110015.11489-1-vincenzo.frascino@arm.com> <198b1486-d402-9061-a6f0-e522a548f040@arm.com> From: Vincenzo Frascino In-Reply-To: <198b1486-d402-9061-a6f0-e522a548f040@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220908_064940_737203_8CCCCC08 X-CRM114-Status: GOOD ( 25.10 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Vladimir, On 9/8/22 11:36, Vladimir Murzin wrote: > Hi Vincenzo, > > On 9/7/22 12:00, Vincenzo Frascino wrote: >> When the kernel is entered on aarch64, the MTE allocation tags are in an >> UNKNOWN state. >> >> With MTE enabled, the tags are initialized: >> - When a page is allocated and the user maps it with PROT_MTE. >> - On allocation, with in-kernel MTE enabled (HW_TAGS KASAN). >> >> If the tag pool is zeroed by the hardware at reset, it makes it >> difficult to track potential places where the initialization of the >> tags was missed. >> >> This can be observed under QEMU for aarch64, which initializes the MTE >> allocation tags to zero. >> >> Initialize to tag storage to KASAN_TAG_INVALID to catch potential >> places where the initialization of the tags was missed. >> >> This is done introducing a new kernel command line parameter >> "mte.tags_init" that enables the debug option. >> >> Note: The proposed solution should be considered a debug option because >> it might have performance impact on large machines at boot. >> >> Cc: Catalin Marinas >> Cc: Will Deacon >> Signed-off-by: Vincenzo Frascino >> --- >> arch/arm64/kernel/mte.c | 47 +++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 47 insertions(+) > > Nothing in Documentation/ ? > I can have a separate patch that adds documentation of the kernel parameter. >> >> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c >> index b2b730233274..af9a8eba9be4 100644 >> --- a/arch/arm64/kernel/mte.c >> +++ b/arch/arm64/kernel/mte.c >> @@ -6,6 +6,7 @@ >> #include >> #include >> #include >> +#include >> #include >> #include >> #include >> @@ -35,6 +36,8 @@ DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode); >> EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode); >> #endif >> >> +static bool mte_tags_init __ro_after_init; >> + >> static void mte_sync_page_tags(struct page *page, pte_t old_pte, >> bool check_swap, bool pte_is_tagged) >> { >> @@ -98,6 +101,48 @@ int memcmp_pages(struct page *page1, struct page *page2) >> return ret; >> } >> >> +/* mte.tags_init=off/on */ >> +static int __init early_mte_tags_init(char *arg) >> +{ >> + if (!arg) >> + return -EINVAL; >> + >> + if (!strcmp(arg, "off")) >> + mte_tags_init = false; >> + else if (!strcmp(arg, "on")) >> + mte_tags_init = true; >> + else >> + return -EINVAL; >> + > > You might want to offload parsing to kstrtobool() > Good point, I was not aware of this API. Thanks! >> + return 0; >> +} >> +early_param("mte.tags_init", early_mte_tags_init); >> + >> +static inline void __mte_tag_storage_init(void) >> +{ >> + static bool mte_tags_uninitialized = true; >> + phys_addr_t pa_start, pa_end; >> + u64 index; >> + >> + if (mte_tags_init && !mte_tags_uninitialized) >> + return; >> + >> + for_each_mem_range(index, &pa_start, &pa_end) { >> + void *va_start = (void *)__phys_to_virt(pa_start); >> + void *va_end = (void *)__phys_to_virt(pa_end); >> + size_t va_size = (u64)va_end - (u64)va_start; >> + >> + if (va_start >= va_end) >> + break; >> + >> + mte_set_mem_tag_range(va_start, va_size, KASAN_TAG_INVALID, false); >> + } >> + >> + /* Tags are now initialized to KASAN_TAG_INVALID */ >> + mte_tags_uninitialized = false; >> + pr_info("MTE: Tag Storage Initialized\n"); > > Why All Words Start With Capital Letter? :D > Do you have any preference? :D > Anyway, you might want to advertise tag value used for initialization. > Yes I agree, I can print "Tag Storage Initialized to 0x.." >> +} >> + >> static inline void __mte_enable_kernel(const char *mode, unsigned long tcf) >> { >> /* Enable MTE Sync Mode for EL1. */ >> @@ -105,6 +150,8 @@ static inline void __mte_enable_kernel(const char *mode, unsigned long tcf) >> SYS_FIELD_PREP(SCTLR_EL1, TCF, tcf)); >> isb(); >> >> + __mte_tag_storage_init(); >> + >> pr_info_once("MTE: enabled in %s mode at EL1\n", mode); >> } >> > > Cheers > Vladimir -- Regards, Vincenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel