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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1755248132; 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-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=a4MNdbvB46xSqJXw/T4+elvNarYzJJ8j5Dig82KsZ5Q=; b=R6p4Gv1XZnaKe5YIx7hQWyKYXIUXrMDllmto9OvwY3XClYQkO+C0D74vggnbaIZ4GM/5QP HB3RsWHAlIKZMmhBFyOFW3BDHJv3HJjlyuLl/u/cnQUPdz+br/aExG37K5luyAmKomsno0 zjVI/IrUYNbD9Dxs132y/BPKf7vyvWE= 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 1CB461E32; Fri, 15 Aug 2025 01:55:23 -0700 (PDT) Received: from e123572-lin.arm.com (e123572-lin.cambridge.arm.com [10.1.194.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B58A63F63F; Fri, 15 Aug 2025 01:55:26 -0700 (PDT) From: Kevin Brodsky To: linux-hardening@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Kevin Brodsky , Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , David Hildenbrand , 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 , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org Subject: [RFC PATCH v5 01/18] mm: Introduce kpkeys Date: Fri, 15 Aug 2025 09:54:55 +0100 Message-ID: <20250815085512.2182322-2-kevin.brodsky@arm.com> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20250815085512.2182322-1-kevin.brodsky@arm.com> References: <20250815085512.2182322-1-kevin.brodsky@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 45A0D140005 X-Stat-Signature: x1ruibesqucdnwpm31mq1pcu5x4ccm3d X-Rspam-User: X-HE-Tag: 1755248132-804544 X-HE-Meta: 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 6Zn6Z2FE bAcT97ykkq+xuHneCtDPkOr8slKoiDAe/E6yKrCuLm8IgYzZrS7N5G+IuKmRg8MvJdI+J3GDdmEOigtwZ83K00IZuAKLFusYUJhUR/TwnZxenlFFhVx6+YYzYM4k6dFMLuz3+bcW+MxtNvSFskqswMrS111Yl14M+QsIWvMOoWkaALXsM5g0mGZYzpFVVcgl4dz0N X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 : - arch_kpkeys_set_level() - arch_kpkeys_restore_pkey_reg() - arch_kpkeys_enabled() Signed-off-by: Kevin Brodsky --- include/asm-generic/kpkeys.h | 17 ++++++ include/linux/kpkeys.h | 113 +++++++++++++++++++++++++++++++++++ mm/Kconfig | 2 + 3 files changed, 132 insertions(+) create mode 100644 include/asm-generic/kpkeys.h create mode 100644 include/linux/kpkeys.h diff --git a/include/asm-generic/kpkeys.h b/include/asm-generic/kpkeys.h new file mode 100644 index 000000000000..ab819f157d6a --- /dev/null +++ b/include/asm-generic/kpkeys.h @@ -0,0 +1,17 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +#ifndef __ASM_GENERIC_KPKEYS_H +#define __ASM_GENERIC_KPKEYS_H + +#ifndef KPKEYS_PKEY_DEFAULT +#define KPKEYS_PKEY_DEFAULT 0 +#endif + +/* + * Represents a pkey register value that cannot be used, typically disabling + * access to all keys. + */ +#ifndef KPKEYS_PKEY_REG_INVAL +#define KPKEYS_PKEY_REG_INVAL 0 +#endif + +#endif /* __ASM_GENERIC_KPKEYS_H */ diff --git a/include/linux/kpkeys.h b/include/linux/kpkeys.h new file mode 100644 index 000000000000..faa6e2615798 --- /dev/null +++ b/include/linux/kpkeys.h @@ -0,0 +1,113 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +#ifndef _LINUX_KPKEYS_H +#define _LINUX_KPKEYS_H + +#include +#include + +#define KPKEYS_LVL_DEFAULT 0 + +#define KPKEYS_LVL_MIN KPKEYS_LVL_DEFAULT +#define KPKEYS_LVL_MAX KPKEYS_LVL_DEFAULT + +#define __KPKEYS_GUARD(name, set_level, restore_pkey_reg, set_arg, ...) \ + __DEFINE_CLASS_IS_CONDITIONAL(name, false); \ + DEFINE_CLASS(name, u64, \ + restore_pkey_reg, set_level, set_arg); \ + static inline void *class_##name##_lock_ptr(u64 *_T) \ + { return _T; } + +/** + * KPKEYS_GUARD_NOOP() - define a guard type that does nothing + * @name: the name of the guard type + * @cond_arg: an argument specification (optional) + * + * Define a guard type that does nothing, useful to match a real guard type + * that is defined under an #ifdef. @cond_arg may optionally be passed to match + * a guard defined using KPKEYS_GUARD_COND(). + */ +#define KPKEYS_GUARD_NOOP(name, ...) \ + __KPKEYS_GUARD(name, 0, (void)_T, ##__VA_ARGS__, void) + +#ifdef CONFIG_ARCH_HAS_KPKEYS + +#include + +/** + * KPKEYS_GUARD_COND() - define a guard type that conditionally switches to + * a given kpkeys level + * @name: the name of the guard type + * @level: the kpkeys level to switch to + * @cond: an expression that is evaluated as condition + * @cond_arg: an argument specification for the condition (optional) + * + * Define a guard type that switches to @level if @cond evaluates to true, and + * does nothing otherwise. @cond_arg may be specified to give access to a + * caller-defined argument to @cond. + */ +#define KPKEYS_GUARD_COND(name, level, cond, ...) \ + __KPKEYS_GUARD(name, \ + cond ? kpkeys_set_level(level) \ + : KPKEYS_PKEY_REG_INVAL, \ + kpkeys_restore_pkey_reg(_T), \ + ##__VA_ARGS__, void) + +/** + * KPKEYS_GUARD() - define a guard type that switches to a given kpkeys level + * if kpkeys are enabled + * @name: the name of the guard type + * @level: the kpkeys level to switch to + * + * Define a guard type that switches to @level if the system supports kpkeys. + */ +#define KPKEYS_GUARD(name, level) \ + KPKEYS_GUARD_COND(name, level, arch_kpkeys_enabled()) + +/** + * kpkeys_set_level() - switch kpkeys level + * @level: the level to switch to + * + * Switches the kpkeys level to the specified value. @level must be a + * compile-time constant. The arch-specific pkey register will be updated + * accordingly, and the original value returned. + * + * Return: the original pkey register value if the register was written to, or + * KPKEYS_PKEY_REG_INVAL otherwise (no write to the register was + * required). + */ +static __always_inline u64 kpkeys_set_level(int level) +{ + BUILD_BUG_ON_MSG(!__builtin_constant_p(level), + "kpkeys_set_level() only takes constant levels"); + BUILD_BUG_ON_MSG(level < KPKEYS_LVL_MIN || level > KPKEYS_LVL_MAX, + "Invalid level passed to kpkeys_set_level()"); + + return arch_kpkeys_set_level(level); +} + +/** + * kpkeys_restore_pkey_reg() - restores a pkey register value + * @pkey_reg: the pkey register value to restore + * + * This function is meant to be passed the value returned by kpkeys_set_level(), + * in order to restore the pkey register to its original value (thus restoring + * the original kpkeys level). + */ +static __always_inline void kpkeys_restore_pkey_reg(u64 pkey_reg) +{ + if (pkey_reg != KPKEYS_PKEY_REG_INVAL) + arch_kpkeys_restore_pkey_reg(pkey_reg); +} + +#else /* CONFIG_ARCH_HAS_KPKEYS */ + +#include + +static inline bool arch_kpkeys_enabled(void) +{ + return false; +} + +#endif /* CONFIG_ARCH_HAS_KPKEYS */ + +#endif /* _LINUX_KPKEYS_H */ diff --git a/mm/Kconfig b/mm/Kconfig index e443fe8cd6cf..90f2e5c381a6 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1173,6 +1173,8 @@ config ARCH_USES_HIGH_VMA_FLAGS bool config ARCH_HAS_PKEYS bool +config ARCH_HAS_KPKEYS + bool config ARCH_USES_PG_ARCH_2 bool -- 2.47.0