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 7620E313E34 for ; Tue, 30 Jun 2026 09:16:41 +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=1782811002; cv=none; b=Y83zCFvL5PTZlKGAaGFM+SaeODa/GiV5H5vY3tWz9Rr2PHxJUT2aPtx7k0kZ4rIDnLV39XPiqaG09wYfpa49eMqnFTDnJugbSJBfeqRzamlPuwi/TZSZNCygA/lvRQEfbnXxXKdb0SNAZLpLDBmWoXZXNPjSRhADLNXNo9keeIk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782811002; c=relaxed/simple; bh=pOGqr+6YjRRrGfqyTm37l0BuFHy9XPuCtkGh7B9Kr+0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=mGE0tGyjnuhSiUpFUusfPUC0xxwq1m3fbDgl1bEvAi5bvfK4e2MZKo38LAB6WRnIcy0Tzx6fyCh6eTU91UClPxhqu09CN4tx96gBWE4bUIdPGPdH6Uvldm5rorZpHHWLItwv6OoQ8+q7zZcDKer/yC7EcOwx72TP5fvR0bHpkcs= 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=OhlBURWG; 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="OhlBURWG" 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 68EE12C1C; Tue, 30 Jun 2026 02:16:36 -0700 (PDT) Received: from [10.57.81.132] (unknown [10.57.81.132]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F30143FAFB; Tue, 30 Jun 2026 02:16:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1782811000; bh=pOGqr+6YjRRrGfqyTm37l0BuFHy9XPuCtkGh7B9Kr+0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=OhlBURWGxQqcbV6J2ZjbPLWqe0+OO9mHDyY8RjjqBPKuIiYpX91UGBHlnRLA2voBR ZGfe8UhEF+CVHnpiOUhkK+Si+HmROlqhNQzZWseJfpnlDEHoIShP9UCusiuqoiShd4 QVu9mycDBfqeZmeTAPiDcXgKfSZGryWFP031nXt4= Message-ID: Date: Tue, 30 Jun 2026 11:16:27 +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 v8 05/24] arm64: Implement asm/kpkeys.h using POE To: "David Hildenbrand (Arm)" , linux-hardening@vger.kernel.org Cc: Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , Ira Weiny , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linus Walleij , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , 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, Lorenzo Stoakes , Thomas Gleixner References: <20260526-kpkeys-v8-0-eaaacdacc67c@arm.com> <20260526-kpkeys-v8-5-eaaacdacc67c@arm.com> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 22/06/2026 15:35, David Hildenbrand (Arm) wrote: > On 5/26/26 13:15, Kevin Brodsky wrote: >> Implement the kpkeys interface if CONFIG_ARM64_POE is enabled. >> The permissions for KPKEYS_PKEY_DEFAULT (pkey 0) are set to RWX as >> this pkey is also used for code mappings. >> >> To allow to be included from assembly, also add >> appropriate #ifdef's to . >> >> Signed-off-by: Kevin Brodsky >> --- >> arch/arm64/include/asm/kpkeys.h | 59 +++++++++++++++++++++++++++++++++++++++++ >> arch/arm64/include/asm/por.h | 4 +++ >> 2 files changed, 63 insertions(+) >> >> diff --git a/arch/arm64/include/asm/kpkeys.h b/arch/arm64/include/asm/kpkeys.h >> new file mode 100644 >> index 000000000000..4dbfeb3dfcfe >> --- /dev/null >> +++ b/arch/arm64/include/asm/kpkeys.h >> @@ -0,0 +1,59 @@ >> +/* SPDX-License-Identifier: GPL-2.0-only */ >> +#ifndef __ASM_KPKEYS_H >> +#define __ASM_KPKEYS_H >> + >> +#include >> +#include >> +#include >> + >> +#include >> + >> +/* >> + * Equivalent to por_set_kpkeys_context(0, KPKEYS_CTX_DEFAULT), but can also be >> + * used in assembly. >> + */ >> +#define POR_EL1_INIT POR_ELx_PERM_PREP(KPKEYS_PKEY_DEFAULT, POE_RWX) > Okay, this matches > > #define POR_EL0_INIT POR_ELx_PERM_PREP(0, POE_RWX) > > Is there a good reason we need KPKEYS_PKEY_DEFAULT at all (and not similarly > just hardcode it to 0)? I did wonder about that. As per the discussion on patch 1 I don't see that value ever changing, so I'm fine with hardcoding 0 if that feels more consistent/intuitive. > Just wondering, because apparently we didn't care about adding an indicator for > user space pkey 0. It's never too late to add a constant for userspace as well, but of course since it's been ABI for so long the value isn't going to change. >> + >> +#ifndef __ASSEMBLY__ >> + >> +static inline bool arch_supports_kpkeys(void) >> +{ >> + return system_supports_poe(); >> +} >> + >> +#ifdef CONFIG_ARM64_POE >> + >> +static inline u64 por_set_kpkeys_context(u64 por, int ctx) >> +{ >> + por = por_elx_set_pkey_perms(por, KPKEYS_PKEY_DEFAULT, POE_RWX); >> + >> + return por; > Why not > > return por_elx_set_pkey_perms(por, KPKEYS_PKEY_DEFAULT, POE_RWX); > > ? Because of patch 17, I wanted to minimise the diff. Happy to change it if that feels less surprising. > In light of API discussions, it would be nicer if arch_kpkeys_set_context() > would just return the old context. But that would mean that restoring the > context would require another read_sysreg_s(SYS_POR_EL1); Correct, that's what I wanted to avoid. > So instead of returning magic register values, that should be wrapped in some > arch state struct as mentioned as reply to a previous patch. Agreed. >> +} >> + >> +static __always_inline void __kpkeys_set_pkey_reg_nosync(u64 pkey_reg) >> +{ >> + write_sysreg_s(pkey_reg, SYS_POR_EL1); >> +} >> + >> +static __always_inline u64 arch_kpkeys_set_context(int ctx) >> +{ >> + u64 prev_por = read_sysreg_s(SYS_POR_EL1); >> + u64 new_por = por_set_kpkeys_context(prev_por, ctx); > Both can be const. Sure. > But maybe you just use a single "por" variable. Not sure how? prev_por is returned and new_por is based on its value. >> + >> + __kpkeys_set_pkey_reg_nosync(new_por); >> + isb(); >> + >> + return prev_por; >> +} >> + >> +static __always_inline void arch_kpkeys_restore_pkey_reg(u64 pkey_reg) >> +{ >> + __kpkeys_set_pkey_reg_nosync(pkey_reg); >> + isb(); > Why is that isb() for both callers outside of the function? Do you expect > another user that doesn't need the isb? Outside of __kpkeys_set_pkey_reg_nosync() that is? That function is also used by patch 22, which doesn't want the ISB because we already have an ISB somewhere else. The naming follows that of __set_pte_nosync(). - Kevin