linux-kernel - [RFC PATCH v2 01/15] mm: Introduce kpkeys

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20250108103250.3188419-2-kevin.brodsky@arm.com>
Date: Wed,  8 Jan 2025 10:32:36 +0000
From: Kevin Brodsky <kevin.brodsky@....com>
To: linux-hardening@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Kevin Brodsky <kevin.brodsky@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mark Brown <broonie@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Jann Horn <jannh@...gle.com>,
	Jeff Xu <jeffxu@...omium.org>,
	Joey Gouly <joey.gouly@....com>,
	Kees Cook <kees@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Andy Lutomirski <luto@...nel.org>,
	Marc Zyngier <maz@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Pierre Langlois <pierre.langlois@....com>,
	Quentin Perret <qperret@...gle.com>,
	"Mike Rapoport (IBM)" <rppt@...nel.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	Qi Zheng <zhengqi.arch@...edance.com>,
	linux-arm-kernel@...ts.infradead.org,
	x86@...nel.org
Subject: [RFC PATCH v2 01/15] mm: Introduce kpkeys

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 a macro 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
<asm/kpkeys.h>, in addition to the macros provided in
<asm-generic/kpkeys.h>:

- arch_kpkeys_set_level()
- arch_kpkeys_restore_pkey_reg()
- arch_kpkeys_enabled()

Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
---
 include/asm-generic/kpkeys.h |  9 +++++
 include/linux/kpkeys.h       | 66 ++++++++++++++++++++++++++++++++++++
 mm/Kconfig                   |  2 ++
 3 files changed, 77 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..3404ce249757
--- /dev/null
+++ b/include/asm-generic/kpkeys.h
@@ -0,0 +1,9 @@
+/* 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
+
+#endif	/* __ASM_GENERIC_KPKEYS_H */
diff --git a/include/linux/kpkeys.h b/include/linux/kpkeys.h
new file mode 100644
index 000000000000..70e44b0db150
--- /dev/null
+++ b/include/linux/kpkeys.h
@@ -0,0 +1,66 @@
+/* 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_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)		\
+	__DEFINE_CLASS_IS_CONDITIONAL(_name, false);			\
+	DEFINE_CLASS(_name, u64,					\
+		     restore_pkey_reg, set_level, void);		\
+	static inline void *class_##_name##_lock_ptr(u64 *_T)		\
+	{ return _T; }
+
+#ifdef CONFIG_ARCH_HAS_KPKEYS
+
+#include <asm/kpkeys.h>
+
+/**
+ * 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.
+ */
+static 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 inline void kpkeys_restore_pkey_reg(u64 pkey_reg)
+{
+	arch_kpkeys_restore_pkey_reg(pkey_reg);
+}
+
+#else /* CONFIG_ARCH_HAS_KPKEYS */
+
+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 1b501db06417..71edc478f111 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1147,6 +1147,8 @@ 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