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 9D169FF886D for ; Tue, 28 Apr 2026 14:17:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type: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=drgZBvdgFovUmyn0F4YsFW+A4FlyUejDfNRWxc71Yvs=; b=HrK/G0Vaon5RxNt5SWNjUXhHJm 0rleXu3Jf6McI0PgU9dF5NDACohwAS7aIKm1sfPvKJzmBQHKhH7uNQsDjkBMUTHFxYz1fo+P+k6oq SSaNBSbuhgRlo6Y7ZraAl4z343ix6bRyfnkd3Quc4VguKDx6qT5yOjKnm9dYgByEpn7pB2a7P9b7j dBpGkZnp7/ldKh/02OzsjszFjYyAJxMchl4tfPcYHNd09eqfIEBGnmDXwLru7yzNWH4JgOm9Kki0z 90e5QOq9iWLO09n5AGicGWxUbfPZZbtCWYjsPp6BcTZz0RPzvMisjNFEdBagVIs6ol1ncX5APQpRy xr8iOPmg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wHjFB-00000001d2N-3J6U; Tue, 28 Apr 2026 14:16:57 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wHjF9-00000001d1P-30Sq for linux-arm-kernel@lists.infradead.org; Tue, 28 Apr 2026 14:16:56 +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 5B03D15A1; Tue, 28 Apr 2026 07:16:47 -0700 (PDT) Received: from [10.57.63.26] (unknown [10.57.63.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0B3763F763; Tue, 28 Apr 2026 07:16:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1777385812; bh=oVrjIdlZ5Ebhd/IWkU1FIsmJ7nMiw5cvbtJC65flWy8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=N9PsyVWZb9ZJ4M1SqH3xQYLnoSiZIX8Z3lJsZWaSwJBJW9JuJqRJAqdYLmCJDIOoE +6rp3bcWLVPNuxuJnN1AV3qfoMKZVRHdgluQweWZSdfqaUSNbDYhKI/zxfpTj6tJ8j FWC1eGlcCi1Fw2SoBRVyxLOvdlknS60k/xbkGuLA= Message-ID: <802ca264-a849-4c66-a27c-db6fa9915711@arm.com> Date: Tue, 28 Apr 2026 16:16:46 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 02/15] mm: Make empty_zero_page __ro_after_init To: Ard Biesheuvel , linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, Ard Biesheuvel , Ryan Roberts , Anshuman Khandual , Liz Prucka , Seth Jenkins , Kees Cook , Mike Rapoport , David Hildenbrand , Andrew Morton , linux-mm@kvack.org, linux-hardening@vger.kernel.org References: <20260427153416.2103979-17-ardb+git@google.com> <20260427153416.2103979-19-ardb+git@google.com> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <20260427153416.2103979-19-ardb+git@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260428_071655_808935_5FE26780 X-CRM114-Status: GOOD ( 17.46 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 27/04/2026 17:34, Ard Biesheuvel wrote: > From: Ard Biesheuvel > > The empty zero page is used to back any kernel or user space mapping > that is supposed to remain cleared, and so the page itself is never > supposed to be modified. > > So make it __ro_after_init rather than __page_aligned_bss: on most > architectures, this ensures that both the kernel's mapping of it and any > aliases that are accessible via the kernel direct (linear) map are > mapped read-only, and cannot be used (inadvertently or maliciously) to > corrupt the contents of the zero page. > > Signed-off-by: Ard Biesheuvel Reviewed-by: Kevin Brodsky > --- > mm/mm_init.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/mm_init.c b/mm/mm_init.c > index f9f8e1af921c..6ca01ed2a5a4 100644 > --- a/mm/mm_init.c > +++ b/mm/mm_init.c > @@ -57,7 +57,7 @@ unsigned long zero_page_pfn __ro_after_init; > EXPORT_SYMBOL(zero_page_pfn); > > #ifndef __HAVE_COLOR_ZERO_PAGE > -uint8_t empty_zero_page[PAGE_SIZE] __page_aligned_bss; > +uint8_t empty_zero_page[PAGE_SIZE] __ro_after_init __aligned(PAGE_SIZE); > EXPORT_SYMBOL(empty_zero_page); > > struct page *__zero_page __ro_after_init;