Re: [PATCH RFC v9 01/25] 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 enter/leave a
kpkeys context and macros to define guard objects.

kpkeys introduces a new concept on top of pkeys: the kpkeys context.
Each context is associated with a set of permissions for the pkeys
managed by the kpkeys framework. kpkeys_enter_context(ctx) sets
those permissions according to ctx, and returns the original kpkeys
state (typically the arch-specific pkeys register) that is later
restored by calling kpkeys_leave_context(). 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).

The underlying representation of each kpkeys context is entirely
architecture-specific. Support for kpkeys must be explicitly
indicated by selecting ARCH_HAS_KPKEYS and defining the following
functions in <asm/kpkeys.h>:

* arch_kpkeys_enter_context()
* arch_kpkeys_leave_context()
* arch_supports_kpkeys()

Additionally, <asm/kpkeys_types.h> must define struct arch_kpkeys_state,
which typically provides storage for the pkeys register.

Signed-off-by: Kevin Brodsky <redacted>

diff --git a/include/linux/kpkeys.h b/include/linux/kpkeys.h
new file mode 100644
index 0000000000000..eac522f552141
--- /dev/null
+++ b/include/linux/kpkeys.h

@@ -0,0 +1,104 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _LINUX_KPKEYS_H
+#define _LINUX_KPKEYS_H
+
+#include <linux/bug.h>
+#include <linux/cleanup.h>
+#include <linux/kpkeys_types.h>
+
+/**
+ * KPKEYS_GUARD_NOOP() - define a guard type that does nothing