From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id F1D8537266D; Fri, 17 Apr 2026 13:11:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776431468; cv=none; b=jfW1ySlFLOnJxSqDnPjuJgBuLGGcC3FRJKBvihtELzbY+guL4LrEe1/I/pfJhFBVI8L8Sem8D4eqpbbxQwO9YNf6LGK8Of2obpiEF6/OkV0RcPz/qvEiewYMW5bONcA+WEIbzT8wdEqm2Vt6NjF/Xl5Q/FDgBedNFfEp7KcNS3c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776431468; c=relaxed/simple; bh=UZ+9QdPmSTx/ezgB1oRSxcs6WFStfM5GyAzSgULBfK0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ViGuuV+BjpGYwZydUt3KfRw+VijEEX/P0UwPqslu3c4RbB6RaMTA3CN5F3VtX5NJg2AIzuFIM+VztF5C3nbzQqu0+jmpKtUh3OpPbGJNN+sR+AMvmKPCO/WDvZnNaQ9vK4VdFP8NbcWCehnRGLZv3/lC0CfpXHs6Rp0XTLZXNqU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=nLP9+NmO; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="nLP9+NmO" 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 1216A1C2B; Fri, 17 Apr 2026 06:10:59 -0700 (PDT) Received: from [10.57.63.31] (unknown [10.57.63.31]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 312443F7D8; Fri, 17 Apr 2026 06:10:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1776431464; bh=UZ+9QdPmSTx/ezgB1oRSxcs6WFStfM5GyAzSgULBfK0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=nLP9+NmOP4Js5PxqLmjA9erzChDc1WNxHz0qocmuG+AsyaZz8t5QVQ1Lo5Rct4eL2 KPNqAe7G2utJg38/pHsrTnSjhvBlhhVTbSoisuYuAhC7ve0hNuyJOThpP/YByANyjN MdbXC7wVzrfGBlCo2N0+cUxzbDtoHJT7TGqJbU94= Message-ID: <5adc64e5-d4e3-42f1-8cf2-6e824bad2bf6@arm.com> Date: Fri, 17 Apr 2026 15:10:52 +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: "David Hildenbrand (Arm)" , 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: Kevin Brodsky Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 17/04/2026 14:00, David Hildenbrand (Arm) wrote: > 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 Sounds good to me, that's more accurate than "level" if it is possible to give access to arbitrary pkeys to each context, which is the current assumption. > 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. Most contexts would, although as I mentioned in the previous email, unprivileged contexts such as eBPF programs may be further restricted. - Kevin