From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0AD60360EF9 for ; Thu, 27 Aug 2026 18:08:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787854135; cv=none; b=A/aPndZ1w997IJcW7O6nyFHuYpoPtfM2+1TeyC3DbFbUnyWjdbrkrFFap1wW90UwVqm3rhxumwpIco/tdwdIQWv4Ozs3tLi0Fuolm36sAT2+2cs12crW6mShHMd5fc/KMxBAM4TftJjfD6AQBiljEEiujGHbotIs5La1/La+RYQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787854135; c=relaxed/simple; bh=kODYJxg2XBntoxe6mQ6p7PAc+UGyZAFGFRo1+Viue6Q=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=e7w1gY329dEoMI8o8tvuHWmYQkg3n0RYhvRpYQ38E5OIuZPny0/E2pwdOneX1YlBIlAz0DrKSRvGT351bGjwmVY/Kk6JSkfKfNb5Ja8AGpzl8j9rTV6FTQVLsILxaCvWcNJ3K02mPrnjDWKXHfJVUL+0t6YI6dQJTZ23cZdSQaE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cXyX6QAc; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cXyX6QAc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D2EAB1F000E9; Thu, 27 Aug 2026 18:08:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787854133; bh=oSl5wDfcIkAZ8O8qomImZnYhRdtX0c0/b/+iSOoYbbQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=cXyX6QAc2K4hCCa6m0zAE3YE+kol844hbwpydqer4TYoxKiPxU9IgtmzJzyCj+b6Q HbZTJJirRawJp6wgO+QFl2O14dCAoQuGY8J5x15vAraWVlo5V1zIEToDQoMvHfTqfF d+bO0MJLxRa/Ek6qVt6J+6z1fa+c06GVGlL+9vE99Bvi+eDwvRd6kwxT0POwAhGNAf ED3biHX6G4Js7XuAL7Expnqsn3eqs9QIJhSf8DYmnz+lVOHdCOgsAa4x/xyB4UcIZe KRQJJPfq+mQnHzMuh0PBCy45zrAFbWhn1Wr0kD+add/DyPLajZyBIyobOu/Vpw368x gHi8Emr0IpY/Q== Message-ID: <1dc8739e-4eb6-4a71-9534-e03a15afd620@kernel.org> Date: Thu, 27 Aug 2026 20:08:44 +0200 Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v9 13/25] mm: kpkeys: Introduce early page table allocator To: Kevin Brodsky , linux-hardening@vger.kernel.org Cc: Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linu Cherian , Linus Walleij , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , =?UTF-8?Q?Pierre-Cl=C3=A9ment_Tosi?= , Quentin Perret , Rick Edgecombe , Ryan Roberts , Vlastimil Babka , Will Deacon , Yang Shi , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org, Ira Weiny , Lorenzo Stoakes , Thomas Gleixner References: <20260818-kpkeys-v9-0-743ad31b2c8f@arm.com> <20260818-kpkeys-v9-13-743ad31b2c8f@arm.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 On 8/18/26 16:08, Kevin Brodsky wrote: > The kpkeys_hardened_pgtables feature aims to protect all page table > pages (PTPs) by mapping them with a privileged pkey. This is primarily > handled by kpkeys_pgtable_alloc(), called from pagetable_alloc(). > However, this does not cover PTPs allocated early, before the > buddy allocator is available. These PTPs are allocated by architecture > code, either 1. from static pools or 2. using the memblock allocator, > and should also be protected. > > This patch addresses the second category: PTPs allocated via memblock. > Such PTPs are notably used to create the linear map. Protecting them as > soon as they are allocated would require modifying the linear map while > it is being created, which seems at best difficult. Instead, a > simple allocator is introduced, obtaining pages from memblock and > keeping track of all allocated ranges to set their pkey once it is > safe to do so. PTPs allocated at that stage are not freed, so there > is no need to manage a free list. I'm think of ways to avoid remembering these ranges. I guess we get called that early that we don't even have a ptdesc where we could just link the pages. If only page tables would be linked in some datastructure where we could find them all ... ;) ... why can't we just scan the page table hierarchy to find all page tables that need protection? -- Cheers, David