mm/core, x86/mm/pkeys: Add arch_validate_pkey()

The syscall-level code is passed a protection key and need to
return an appropriate error code if the protection key is bogus.
We will be using this in subsequent patches.

Note that this also begins a series of arch-specific calls that
we need to expose in otherwise arch-independent code.  We create
a linux/pkeys.h header where we will put *all* the stubs for
these functions.

Signed-off-by: Dave Hansen <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

arch/x86/Kconfig

@@ -156,6 +156,7 @@ config X86
 	select X86_DEV_DMA_OPS			if X86_64
 	select X86_FEATURE_NAMES		if PROC_FS
 	select ARCH_USES_HIGH_VMA_FLAGS		if X86_INTEL_MEMORY_PROTECTION_KEYS
+	select ARCH_HAS_PKEYS			if X86_INTEL_MEMORY_PROTECTION_KEYS
 
 config INSTRUCTION_DECODER
 	def_bool y

arch/x86/include/asm/pkeys.h

@@ -0,0 +1,6 @@
+#ifndef _ASM_X86_PKEYS_H
+#define _ASM_X86_PKEYS_H
+
+#define arch_max_pkey() (boot_cpu_has(X86_FEATURE_OSPKE) ? 16 : 1)
+
+#endif /*_ASM_X86_PKEYS_H */

include/linux/pkeys.h

@@ -0,0 +1,25 @@
+#ifndef _LINUX_PKEYS_H
+#define _LINUX_PKEYS_H
+
+#include <linux/mm_types.h>
+#include <asm/mmu_context.h>
+
+#ifdef CONFIG_ARCH_HAS_PKEYS
+#include <asm/pkeys.h>
+#else /* ! CONFIG_ARCH_HAS_PKEYS */
+#define arch_max_pkey() (1)
+#endif /* ! CONFIG_ARCH_HAS_PKEYS */
+
+/*
+ * This is called from mprotect_pkey().
+ *
+ * Returns true if the protection keys is valid.
+ */
+static inline bool validate_pkey(int pkey)
+{
+	if (pkey < 0)
+		return false;
+	return (pkey < arch_max_pkey());
+}
+
+#endif /* _LINUX_PKEYS_H */

mm/Kconfig

@@ -672,3 +672,5 @@ config FRAME_VECTOR
 
 config ARCH_USES_HIGH_VMA_FLAGS
 	bool
+config ARCH_HAS_PKEYS
+	bool