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 C941EFF886D for ; Tue, 28 Apr 2026 19:51:25 +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=N5ioFK0mHY9Ys4LHm2ud15cUW/kDvfazRIYlH++roFY=; b=IRvsQjPmhr7CGH4jxydotJ7rnD u9XGhGMw5akQr/xFN4dBWpmCfyHAV60DbTz0rWmJmYogiLFiYlsGURrPDlvwQZI/YuGOshT+7oY0u X4pvPN6+rIMNLyyuP5X7tggyKQk62wGRrlG8ygx1tudFEkYDMoWTURGhWwagS+cZQp4OLeAJkpFzu gOeYpvJCIOroE1QA7AFLqWvrW+Pjit/+8F+8o1dWCUgzrObMFB0qCbidasLdovz/KEKU8xSeYGBOu xogkRrVi/eN9EcPae8zdS/3udNy+dZXButyTtfXlzUXDoMhFtVDpu/fsrduZPhZ3MePMPylc5Sj1Q NXa0C94w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wHoSm-00000002BKW-0PxE; Tue, 28 Apr 2026 19:51:20 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1wHoSj-00000002BKN-3uUb for linux-arm-kernel@lists.infradead.org; Tue, 28 Apr 2026 19:51:18 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id EC5E161145; Tue, 28 Apr 2026 19:51:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EFA90C2BCAF; Tue, 28 Apr 2026 19:51:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777405876; bh=Nhfmyw9bPmtRKlxPV1In2mC53XW8ms1qpcByR8ySSaY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=nm3/Up7Fte+HsSj4Zi+YOwznbJD7iPvMtnYo665KKkx6dWJcE7Gzd0pPiMSQo+jK4 jne31Wtcxx5AG8x5gUZVH9V8RjxMZw7APbTvdkucjJW3hbn/Kxv2fYWn4d4iNwidcq oxgP3xyTt8eJTpuPlhI6M7N8t55F9QFPaHEBiZMxlU5purCnr6aeQmlod1arAb7qyT TejgemR812N9nuTYeJuBNAVDkdX15SepZsM2cm3UB+os/1GK6MzazI8reQvK4XdYJx 2vglztBGG3fVOstGGeKmJzZujOc0herLstlCzqy++2TxoMjnhbtu7LcpirMLnVykhl 0WusTNZOxXBdA== Message-ID: <3d1a6b5c-f3bf-462f-879a-cdb5b60868ac@kernel.org> Date: Tue, 28 Apr 2026 21:51:09 +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 , 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: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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 4/27/26 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 > --- > 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; I am no expert on BSS etc, but from what I understand, we'll still get zeroed page-aligned memory. I don't know if there is any other impact on not having it in bss.page_aligned. I assume no Acked-by: David Hildenbrand (Arm) -- Cheers, David