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bh=guqrDTBg9L+rMmzwHLEGhZCrOb5ASxmVe+Yvhw85EsE=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=mgXyVOhPh5Ym8PaAy/kc/vKjTdJycVt1gR+XQakLOLXLXMPMA9SKf4u2j9sYFRd9i aOEwPgI21nLFRvV6Ia0IoxWtjQG+Vens5CoW5haUDSrRhdGKh1VzI03uWp9YRrz/fh gqptUhdgLtjrDdzyHwRLzOxfYrR8cC3/jIKaYTBs= From: Kevin Brodsky Date: Tue, 26 May 2026 12:15:50 +0100 Subject: [PATCH RFC v8 01/24] mm: Introduce kpkeys MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260526-kpkeys-v8-1-eaaacdacc67c@arm.com> References: <20260526-kpkeys-v8-0-eaaacdacc67c@arm.com> In-Reply-To: <20260526-kpkeys-v8-0-eaaacdacc67c@arm.com> To: linux-hardening@vger.kernel.org Cc: Kevin Brodsky , Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , "David Hildenbrand (Arm)" , 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 X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1779794211; l=6647; i=kevin.brodsky@arm.com; s=20260427; h=from:subject:message-id; bh=guqrDTBg9L+rMmzwHLEGhZCrOb5ASxmVe+Yvhw85EsE=; b=oPJXA+ORDOej1DfFtYeT+KvUWZRlr0MxVa1EQKUPKgt4IXJnjaOVA4turG7Yc1iDLet8vQuRs viYfkErkNpxDLE0InZj9u2G7iaznYEJvG8TQ3z7WrySKrLaXBYgqDXT X-Developer-Key: i=kevin.brodsky@arm.com; a=ed25519; pk=N2QG+eJKrvkNovwhhwJhnJ4+ScVfsGCHldmqLfcMTFs= X-Stat-Signature: u7eh3g49qm95hnctwfb7dx7kz671oro3 X-Rspamd-Queue-Id: B7732160011 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1779794223-872799 X-HE-Meta: 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 aMO4PqgO RgSH4uSjTta0JJVycNzTLcBc0ggTxC+qYcZqLAXCfqAKTC7lu0IcCle2h8vGzJw8MBpwIQg34dzT2vMf/Rct6mNBX8TEu9UxJ1QTUnAlOFDAhQMQ69YPD4zZs4mKD+HiGqTeZr9eIMraKp4YG5OT0KJYPIpnboX4KWUNpm/0WWh29TQyUclrWZm6o9PF0/X593DY/gwIS1DICpgLavl+wVGshJnLMgt1u+ApcX5mjnmhUX2u5E95XY7Lpa7A0n79bksSqa8OZMt9pFC4hdmBuVsPRkDt+gOawULPx 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 context. Each context is associated to a set of permissions for the pkeys managed by the kpkeys framework. kpkeys_set_context(ctx) sets those permissions according to ctx, and returns the original pkey register, to be later restored by kpkeys_restore_pkey_reg(). To start with, only KPKEYS_CTX_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_context() - arch_kpkeys_restore_pkey_reg() - arch_supports_kpkeys() Signed-off-by: Kevin Brodsky --- include/asm-generic/kpkeys.h | 17 ++++++ include/linux/kpkeys.h | 122 +++++++++++++++++++++++++++++++++++++++++++ mm/Kconfig | 2 + 3 files changed, 141 insertions(+) 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..0ce0db80b4ee --- /dev/null +++ b/include/linux/kpkeys.h @@ -0,0 +1,122 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +#ifndef _LINUX_KPKEYS_H +#define _LINUX_KPKEYS_H + +#include +#include + +#define KPKEYS_CTX_DEFAULT 0 + +#define KPKEYS_CTX_MIN KPKEYS_CTX_DEFAULT +#define KPKEYS_CTX_MAX KPKEYS_CTX_DEFAULT + +/* + * ... is used to discard extra arguments - this allows users of this macro + * to have set_arg default to void. + */ +#define __KPKEYS_GUARD(name, set_context, restore_pkey_reg, set_arg, ...) \ + __DEFINE_CLASS_IS_CONDITIONAL(name, false); \ + DEFINE_CLASS(name, u64, \ + restore_pkey_reg, set_context, 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 context + * @name: the name of the guard type + * @ctx: the kpkeys context 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 @ctx 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, ctx, cond, ...) \ + __KPKEYS_GUARD(name, \ + (cond) ? kpkeys_set_context(ctx) \ + : KPKEYS_PKEY_REG_INVAL, \ + kpkeys_restore_pkey_reg(_T), \ + ##__VA_ARGS__, void) + +/** + * KPKEYS_GUARD() - define a guard type that switches to a given kpkeys context + * if kpkeys are enabled + * @name: the name of the guard type + * @ctx: the kpkeys context to switch to + * + * Define a guard type that switches to @ctx if the system supports kpkeys. + */ +#define KPKEYS_GUARD(name, ctx) \ + KPKEYS_GUARD_COND(name, ctx, kpkeys_enabled()) + +/** + * kpkeys_set_context() - switch kpkeys context + * @ctx: the context to switch to + * + * Switches to specified kpkeys context. @ctx 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_context(int ctx) +{ + BUILD_BUG_ON_MSG(!__builtin_constant_p(ctx), + "kpkeys_set_context() only takes constant values"); + BUILD_BUG_ON_MSG(ctx < KPKEYS_CTX_MIN || ctx > KPKEYS_CTX_MAX, + "Invalid value passed to kpkeys_set_context()"); + + return arch_kpkeys_set_context(ctx); +} + +/** + * 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_context(), in order to restore the pkey register to its original + * value (thus restoring the original kpkeys context). + */ +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); +} + +static inline bool kpkeys_enabled(void) +{ + return arch_supports_kpkeys(); +} + +#else /* CONFIG_ARCH_HAS_KPKEYS */ + +#include + +static inline bool kpkeys_enabled(void) +{ + return false; +} + +#endif /* CONFIG_ARCH_HAS_KPKEYS */ + +#endif /* _LINUX_KPKEYS_H */ diff --git a/mm/Kconfig b/mm/Kconfig index e8bf1e9e6ad9..819fb0d7b7bd 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1242,6 +1242,8 @@ config ARCH_USES_HIGH_VMA_FLAGS bool config ARCH_HAS_PKEYS bool +config ARCH_HAS_KPKEYS + bool config ARCH_USES_PG_ARCH_2 bool -- 2.51.2