From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 5DEC42E9757; Fri, 17 Apr 2026 12:01:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776427263; cv=none; b=tbXJrM0u+9ayiLa7QR9SHsjOfU6F4b3lgt1nfd/CJv1cy3i5jLhWAqSl2eXpjuGuZgxnzWuCTOwjZu0sCYfRSghRI4EV8NMELnTJj0hEWnO6olH/f2o2EYVqPNak6OpAhRE3NbsA2XfI1/Nxzs7Yzu6ExmlYlqx3dzcxm4K3fJU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776427263; c=relaxed/simple; bh=mU3rZj67IqrTTnj++/n+dIVHR+LNXGChH2TwgHtrl7c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=P5ekKViEpZQt/YUovM/GdZMIcLTl17/+jWTLPfw+dN2jIgf0pwR5IdQZdm0jGpW0gqkq4Qu+Mx8HBotqsAfGpFzZ0dd4nBpNj4Z1mMrj3kaKCyT3CRJ6NdZuVXg6bEpp7scT5AAdu6fcCP1xqkn09BNgwuhstgGBOLZI1WTnzIE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gixXRhDe; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="gixXRhDe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2638AC19425; Fri, 17 Apr 2026 12:00:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776427263; bh=mU3rZj67IqrTTnj++/n+dIVHR+LNXGChH2TwgHtrl7c=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=gixXRhDebXpKk32RlamutnzhZ1GLLADsv69hPJWEWYEjKtp3w8dF8lF6PgtCGdwZM tHyhMMIUE1WhuCUXAIevFo9WCqiNv6W5zqdELOSVxL8JkzeDVQP/bUGzP00tcpX5Me 8noj3V3GvefKdJTw10NZe+Dl1Qh7flMuer7J7K+UfzlR//frRT9NBnPz7gyBws+jj5 xD5K/9xYPH3+BjB4PtpVCdRXZvdqpJXiJtSCkbniaMGj83hycL+c6WB0+res+2nkir 1EB5YpMtEuQeKnM0Z7JXWRYUpCp3tkdfiWJmZrf6xu1CNqzLIqcS3OMLbBNOnef/jQ OoJolHOLfmzOg== Message-ID: Date: Fri, 17 Apr 2026 14:00:53 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 01/30] mm: Introduce kpkeys To: Kevin Brodsky , linux-hardening@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , Ira Weiny , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linus Walleij , Lorenzo Stoakes , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , Quentin Perret , Rick Edgecombe , Ryan Roberts , Thomas Gleixner , Vlastimil Babka , Will Deacon , Yang Shi , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org References: <20260227175518.3728055-1-kevin.brodsky@arm.com> <20260227175518.3728055-2-kevin.brodsky@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 4/15/26 17:50, Kevin Brodsky wrote: > On 15/04/2026 15:00, David Hildenbrand (Arm) wrote: >> On 2/27/26 18:54, Kevin Brodsky wrote: >>> kpkeys is a simple framework to enable the use of protection keys >>> (pkeys) to harden the kernel itself. This patch introduces the basic >>> API in : a couple of functions to set and restore >>> the pkey register and macros to define guard objects. >>> >>> kpkeys introduces a new concept on top of pkeys: the kpkeys level. >>> Each level is associated to a set of permissions for the pkeys >>> managed by the kpkeys framework. kpkeys_set_level(lvl) sets those >>> permissions according to lvl, and returns the original pkey >>> register, to be later restored by kpkeys_restore_pkey_reg(). To >>> start with, only KPKEYS_LVL_DEFAULT is available, which is meant >>> to grant RW access to KPKEYS_PKEY_DEFAULT (i.e. all memory since >>> this is the only available pkey for now). >>> >>> Because each architecture implementing pkeys uses a different >>> representation for the pkey register, and may reserve certain pkeys >>> for specific uses, support for kpkeys must be explicitly indicated >>> by selecting ARCH_HAS_KPKEYS and defining the following functions in >>> , in addition to the macros provided in >>> : >> I don't quite understand the reason for using levels. Levels sounds like >> it would all be in some ordered fashion, where higher levels have access >> to lower levels. > > That was originally the idea indeed, but in practice I don't expect > levels to have a strict ordering, as it's not practical for composing > features. > >> Think of that as a key that can unlock all "lower" locks, not just a >> single lock. >> >> Then, the question is about the ordering once we introduce new >> keys/locks. With two, it obviously doesn't matter :) >> >> So naturally I wonder whether levels is really the right abstraction >> here, and why we are not simply using "distinct" keys, like >> >> KPKEY_DEFAULT >> KPKEY_PGTABLE >> KPKEY_SUPER_SECRET1 >> KPKEY_SUPER_SECRET2 >> >> Is it because you want KPKEY_PGTABLE also be able to write to KPKEY_DEFAULT? > > Right, and in general a given level may be able to write to any number > of pkeys. That's why I don't want to conflate pkeys and levels. Agreed > that "level" might not be the clearest term though, since there's no > strict ordering. As discussed offline, maybe the right terminology to use here would be something like a "context". You'd be activating/setting a context. KPKEY_CTX_DEFAULT KPKEY_CTX_PGTABLE KPKEY_CTX_SUPER_SECRET1 What is accessible (and how) is defined for each context. For example, I would assume that all context allow for read/write access to everything that KPKEY_CTX_DEFAULT has access to. -- Cheers, David