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 <linux/kpkeys.h>: 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 <asm/kpkeys.h>, in addition to the macros provided in <asm-generic/kpkeys.h>: - arch_kpkeys_set_context() - arch_kpkeys_restore_pkey_reg() - arch_supports_kpkeys() Signed-off-by: Kevin Brodsky <[email protected]> --- include/asm-generic/kpkeys.h | 17 +++++++ include/linux/kpkeys.h | 118 +++++++++++++++++++++++++++++++++++++++++++ mm/Kconfig | 2 + 3 files changed, 137 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..cb2d22758391 --- /dev/null +++ b/include/linux/kpkeys.h @@ -0,0 +1,118 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +#ifndef _LINUX_KPKEYS_H +#define _LINUX_KPKEYS_H + +#include <linux/bug.h> +#include <linux/cleanup.h> + +#define KPKEYS_CTX_DEFAULT 0 + +#define KPKEYS_CTX_MIN KPKEYS_CTX_DEFAULT +#define KPKEYS_CTX_MAX KPKEYS_CTX_DEFAULT + +#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 <asm/kpkeys.h> + +/** + * 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 <asm-generic/kpkeys.h> + +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
