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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 66B51CD3447 for ; Sat, 9 May 2026 11:05:02 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 422136B00EB; Sat, 9 May 2026 07:05:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2E8446B013D; Sat, 9 May 2026 07:05:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1D7D46B00EB; Sat, 9 May 2026 07:05:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 08C3D6B0316 for ; Sat, 9 May 2026 07:05:01 -0400 (EDT) Received: from smtpin13.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id BB6ED1C0502 for ; Sat, 9 May 2026 11:05:00 +0000 (UTC) X-FDA: 84747599160.13.76E3A8A Received: from fhigh-b7-smtp.messagingengine.com (fhigh-b7-smtp.messagingengine.com [202.12.124.158]) by imf05.hostedemail.com (Postfix) with ESMTP id A010210000A for ; Sat, 9 May 2026 11:04:58 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=shutemov.name header.s=fm1 header.b="i YHwp/X"; dkim=pass header.d=messagingengine.com header.s=fm3 header.b=WWrwA2q5; dmarc=none; spf=pass (imf05.hostedemail.com: domain of kirill@shutemov.name designates 202.12.124.158 as permitted sender) smtp.mailfrom=kirill@shutemov.name ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1778324698; a=rsa-sha256; cv=none; b=GPHMnGQbfq2apLe1v+oQVFednSJBdn87tbyd2u7ZcJK4RVmOPxM2TqOHiHM9XkxL6PU5qD 9Td4gAUueFiUABd4xA1rBAb7exr/GB+xNi7NzkokMssP7e1VULQr7VmQSlFpuyfb4a2Axn 1ilUn/4vbGZbydQszbtrprQ8LaFi0L8= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=shutemov.name header.s=fm1 header.b="i YHwp/X"; dkim=pass header.d=messagingengine.com header.s=fm3 header.b=WWrwA2q5; dmarc=none; spf=pass (imf05.hostedemail.com: domain of kirill@shutemov.name designates 202.12.124.158 as permitted sender) smtp.mailfrom=kirill@shutemov.name ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1778324698; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=6oOr15lhB2hYKh+9zKzPi4kv7JyYr4PGQI35DlaGm7s=; b=wZz+hXZ31tfw9W10kveqs3nnULsPhBmTYtCAfLC3YDEZIYxE6B7ubHiS28IC6puC1zic4p JS2ikYVqPtAA3gG7W8jA4b4RTQ8UAqtnLP4FHU4KfjKXqBWRvBEyYCQUnwjEk4BPy0S1ac uB1HRKFlWYs02etNnuFEv0XPEYbpHJU= Received: from phl-compute-03.internal (phl-compute-03.internal [10.202.2.43]) by mailfhigh.stl.internal (Postfix) with ESMTP id A1D357A00BC; Sat, 9 May 2026 07:04:56 -0400 (EDT) Received: from phl-frontend-03 ([10.202.2.162]) by phl-compute-03.internal (MEProxy); Sat, 09 May 2026 07:04:57 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov.name; h=cc:cc:content-type:content-type:date:date:from:from :in-reply-to:in-reply-to:message-id:mime-version:references :reply-to:subject:subject:to:to; s=fm1; t=1778324696; x= 1778411096; bh=6oOr15lhB2hYKh+9zKzPi4kv7JyYr4PGQI35DlaGm7s=; b=i YHwp/XRv0gFo5lo0yIQ7J3BAhxjKzc3qK9tshRBnSUZQ7Mp9aH96+Wpnu1y3GWU3 UXBfnZHHE6GUePMKSrbBXQJuHtmVhe/9KdUqGG9+g4zhdo82l7Zcl1wNVDqlWfBm 0HyAlYwth+3lEoTET+zje/53ySJiy7rVG5PyRC/qflCORE5ANufiF3gyvsqWuejS ZVvEM4pS0vD0A/QbxyDRXtHCw20oKudQDFFA2vBKGA/Scp+UFHsrubM4oYb3YfFc 0c7fd9TxoTejQVLLp8+rWmDTLqsAcWkkeCMi+qXc9w4jFWta2dg1XrRt9DqPoEyz mI4Y4mK1w9pcw9kRHdNuA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-type:content-type:date:date :feedback-id:feedback-id:from:from:in-reply-to:in-reply-to :message-id:mime-version:references:reply-to:subject:subject:to :to:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s=fm3; t= 1778324696; x=1778411096; bh=6oOr15lhB2hYKh+9zKzPi4kv7JyYr4PGQI3 5DlaGm7s=; b=WWrwA2q5wWAbrLhsibxkrHgSeKPAYsHWw5tDREWL+X9KWWCjoOm Tj0iUCm3Rmp6aAVYyK0yk+R+NKby83yPn53wIwthTfHnJz78Oa+JTVE6rGNRep91 2Of0ERtNC5HHgqoOtjNNXOjXKmsdfZCqArYTECWPnOhPpkIjBdwdNRjI3iayuNW0 Ku4e941xohI8IdchY9oU3+dABYK1gmmjISegRnmXW+cjZopAT5nlGzrBtEgMXa3y qCIx5172E05QgX+I87hfNYsFpD260mMQHZrZOJhi9LrA3VMcHTU3EerU5NK3G0iJ 4UA1Q7m4UdN+qOzIBTgOpGiEV+Tkcj6jVig== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefhedrtddtgdduudeftdeiucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfurfetoffkrfgpnffqhgenuceu rghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujf gurhepfffhvfevuffkfhggtggujgesthdtredttddtvdenucfhrhhomhepmfhirhihlhcu ufhhuhhtshgvmhgruhcuoehkihhrihhllhesshhhuhhtvghmohhvrdhnrghmvgeqnecugg ftrfgrthhtvghrnhepfeetheejudeujeeikeetudelvdevkeefuddtkedvtdehtdetieeu ieetjeeugedtnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrh homhepkhhirhhilhhlsehshhhuthgvmhhovhdrnhgrmhgvpdhnsggprhgtphhtthhopeef gedpmhhouggvpehsmhhtphhouhhtpdhrtghpthhtohepuggrvhhiugeskhgvrhhnvghlrd horhhgpdhrtghpthhtoheprghruggsodhgihhtsehgohhoghhlvgdrtghomhdprhgtphht thhopehlihhnuhigqdgrrhhmqdhkvghrnhgvlheslhhishhtshdrihhnfhhrrgguvggrug drohhrghdprhgtphhtthhopehlihhnuhigqdhkvghrnhgvlhesvhhgvghrrdhkvghrnhgv lhdrohhrghdprhgtphhtthhopeifihhllheskhgvrhhnvghlrdhorhhgpdhrtghpthhtoh eptggrthgrlhhinhdrmhgrrhhinhgrshesrghrmhdrtghomhdprhgtphhtthhopehmrghr khdrrhhuthhlrghnugesrghrmhdrtghomhdprhgtphhtthhopegrrhgusgeskhgvrhhnvg hlrdhorhhgpdhrtghpthhtoheprhihrghnrdhrohgsvghrthhssegrrhhmrdgtohhm X-ME-Proxy: Feedback-ID: ie3994620:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Sat, 9 May 2026 07:04:54 -0400 (EDT) Date: Sat, 9 May 2026 12:04:47 +0100 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Ard Biesheuvel , linux-arm-kernel@lists.infradead.org, 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 Subject: Re: [PATCH v4 02/15] mm: Make empty_zero_page __ro_after_init Message-ID: References: <20260427153416.2103979-17-ardb+git@google.com> <20260427153416.2103979-19-ardb+git@google.com> <3d1a6b5c-f3bf-462f-879a-cdb5b60868ac@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3d1a6b5c-f3bf-462f-879a-cdb5b60868ac@kernel.org> X-Stat-Signature: 63jhoxdxyxemyoez3w9yfb6qzbnsx3kp X-Rspam-User: X-Rspamd-Queue-Id: A010210000A X-Rspamd-Server: rspam07 X-HE-Tag: 1778324698-774682 X-HE-Meta: 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 YAw0tgyB 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Apr 28, 2026 at 09:51:09PM +0200, David Hildenbrand (Arm) wrote: > 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 IIUC, unlike BSS, it will be part of the kernel image. So kernel image size will grow by PAGE_SIZE. But compressor will eat it as it is all zeros, so it should be okay. -- Kiryl Shutsemau / Kirill A. Shutemov