[PATCH V9 10/45] mm/pkeys: Provide for PKS key allocation

[ira . weiny]

From: Ira Weiny <ira.weiny@xxxxxxxxx>

Kernel consumers of PKS need a way to allocate a PKS pkey and assign the
initial permissions for that key.  It is desirable to not allocate keys
for consumers which are not configured.

Introduce a macro to allocate keys sequentially based on which consumers
are configured.  In addition define a macro to set the proper permission
bits based on the actual pkey value allocated.

pks-keys.h is added as a new header with minimal header dependencies.
This allows the use of PKS_INIT_VALUE within other headers where the
additional includes from other pkey headers caused major conflicts.  The
main conflict was using PKS_INIT_VALUE for INIT_TRHEAD in
asm/processor.h

Add documentation.

Suggested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>

---
Changes for V9
	Reword the commit message
	Move this patch ahead of the enable patch so that the enable
		patch can use PKS_INIT_VALUE
	From Dan Williams
		Use Dan's macro magic
			enhanced it to account for the max number of
			keys
		Update documentation for the change
	From Dave Hansen
		use pkey
		s/PKR_RW_KEY/PKR_RW_MASK

Changes for V8
	Create pks-keys.h to solve header conflicts in subsequent
		patches.
	Remove create_initial_pkrs_value() which did not work
		Replace it with PKS_INIT_VALUE
		Fix up documentation to match
	s/PKR_RW_BIT/PKR_RW_KEY()/
	s/PKRS_INIT_VALUE/PKS_INIT_VALUE
	Split this off of the previous patch
	Update documentation and embed it in the code to help ensure it
	is kept up to date.

Changes for V7
	Create a dynamic pkrs_initial_value in early init code.
	Clean up comments
	Add comment to macro guard
---
 Documentation/core-api/protection-keys.rst |  5 ++
 arch/x86/include/asm/pkeys_common.h        |  9 ++-
 include/linux/pks-keys.h                   | 78 ++++++++++++++++++++++
 3 files changed, 91 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/pks-keys.h

diff --git a/Documentation/core-api/protection-keys.rst b/Documentation/core-api/protection-keys.rst
index 13eedb0119e1..d501bd27ee29 100644
--- a/Documentation/core-api/protection-keys.rst
+++ b/Documentation/core-api/protection-keys.rst
@@ -131,3 +131,8 @@ ARCH_HAS_SUPERVISOR_PKEYS.  It also makes it possible for multiple independent
 features to "select ARCH_ENABLE_SUPERVISOR_PKEYS".  If no features enable PKS
 by selecting ARCH_ENABLE_SUPERVISOR_PKEYS, PKS support will not be compiled
 into the kernel.
+
+PKS Key Allocation
+------------------
+.. kernel-doc:: include/linux/pks-keys.h
+        :doc: PKS_KEY_ALLOCATION
diff --git a/arch/x86/include/asm/pkeys_common.h b/arch/x86/include/asm/pkeys_common.h
index 359b94cdcc0c..b28a72dea22b 100644
--- a/arch/x86/include/asm/pkeys_common.h
+++ b/arch/x86/include/asm/pkeys_common.h
@@ -2,10 +2,17 @@
 #ifndef _ASM_X86_PKEYS_COMMON_H
 #define _ASM_X86_PKEYS_COMMON_H
 
+#define PKS_NUM_PKEYS 16
+#define PKS_ALL_AD (0x55555555UL)
+
 #define PKR_AD_BIT 0x1u
 #define PKR_WD_BIT 0x2u
 #define PKR_BITS_PER_PKEY 2
 
-#define PKR_AD_MASK(pkey)	(PKR_AD_BIT << ((pkey) * PKR_BITS_PER_PKEY))
+#define PKR_PKEY_SHIFT(pkey)	(pkey * PKR_BITS_PER_PKEY)
+
+#define PKR_RW_MASK(pkey)	(0          << PKR_PKEY_SHIFT(pkey))
+#define PKR_AD_MASK(pkey)	(PKR_AD_BIT << PKR_PKEY_SHIFT(pkey))
+#define PKR_WD_MASK(pkey)	(PKR_WD_BIT << PKR_PKEY_SHIFT(pkey))
 
 #endif /*_ASM_X86_PKEYS_COMMON_H */
diff --git a/include/linux/pks-keys.h b/include/linux/pks-keys.h
new file mode 100644
index 000000000000..c914afecb2d3
--- /dev/null
+++ b/include/linux/pks-keys.h
@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_PKS_KEYS_H
+#define _LINUX_PKS_KEYS_H
+
+/*
+ * The contents of this header should be limited to assigning PKS keys and
+ * default values to avoid intricate header dependencies.
+ */
+
+#ifdef CONFIG_ARCH_ENABLE_SUPERVISOR_PKEYS
+
+#include <asm/pkeys_common.h>
+
+#define PKS_NEW_KEY(prev, config) \
+	(prev + __is_defined(config))
+#define PKS_DECLARE_INIT_VALUE(pkey, value, config) \
+	(PKR_##value##_MASK(pkey) * __is_defined(config))
+
+/**
+ * DOC: PKS_KEY_ALLOCATION
+ *
+ * Users reserve a key value in 5 steps.
+ *	1) Use PKS_NEW_KEY to create a new key
+ *	2) Ensure that the last key value is specified in the PKS_NEW_KEY macro
+ *	3) Adjust PKS_KEY_MAX to use the newly defined key value
+ *	4) Use PKS_DECLARE_INIT_VALUE to define an initial value
+ *	5) Add the new PKS default value to PKS_INIT_VALUE
+ *
+ * The PKS_NEW_KEY and PKS_DECLARE_INIT_VALUE macros require the Kconfig
+ * option to be specified to automatically adjust the number of keys used.
+ *
+ * PKS_KEY_DEFAULT must remain 0 with a default of PKS_DECLARE_INIT_VALUE(...,
+ * RW, ...) to support non-pks protected pages.
+ *
+ * Example: to configure a key for 'MY_FEATURE' with a default of Write
+ * Disabled.
+ *
+ * .. code-block:: c
+ *
+ *	#define PKS_KEY_DEFAULT		0
+ *
+ *	// 1) Use PKS_NEW_KEY to create a new key
+ *	// 2) Ensure that the last key value is specified (eg PKS_KEY_DEFAULT)
+ *	#define PKS_KEY_MY_FEATURE PKS_NEW_KEY(PKS_KEY_DEFAULT, CONFIG_MY_FEATURE)
+ *
+ *	// 3) Adjust PKS_KEY_MAX
+ *	#define PKS_KEY_MAX	   PKS_NEW_KEY(PKS_KEY_MY_FEATURE, 1)
+ *
+ *	// 4) Define initial value
+ *	#define PKS_KEY_MY_FEATURE_INIT PKS_DECLARE_INIT_VALUE(PKS_KEY_MY_FEATURE, \
+ *								WD, CONFIG_MY_FEATURE)
+ *
+ *
+ *	// 5) Add initial value to PKS_INIT_VALUE
+ *	#define PKS_INIT_VALUE ((PKS_ALL_AD & PKS_ALL_AD_MASK) | \
+ *				PKS_KEY_DEFAULT_INIT | \
+ *				PKS_KEY_MY_FEATURE_INIT \
+ *				)
+ */
+
+/* PKS_KEY_DEFAULT must be 0 */
+#define PKS_KEY_DEFAULT		0
+#define PKS_KEY_MAX		PKS_NEW_KEY(PKS_KEY_DEFAULT, 1)
+
+/* PKS_KEY_DEFAULT_INIT must be RW */
+#define PKS_KEY_DEFAULT_INIT	PKS_DECLARE_INIT_VALUE(PKS_KEY_DEFAULT, RW, 1)
+
+#define PKS_ALL_AD_MASK \
+	GENMASK(PKS_NUM_PKEYS * PKR_BITS_PER_PKEY, \
+		PKS_KEY_MAX * PKR_BITS_PER_PKEY)
+
+#define PKS_INIT_VALUE ((PKS_ALL_AD & PKS_ALL_AD_MASK) | \
+			PKS_KEY_DEFAULT_INIT \
+			)
+
+#endif /* CONFIG_ARCH_ENABLE_SUPERVISOR_PKEYS */
+
+#endif /* _LINUX_PKS_KEYS_H */
-- 
2.35.1