mm: introduce execmem_alloc() and execmem_free()

module_alloc() is used everywhere as a mean to allocate memory for code.

Beside being semantically wrong, this unnecessarily ties all subsystems
that need to allocate code, such as ftrace, kprobes and BPF to modules and
puts the burden of code allocation to the modules code.

Several architectures override module_alloc() because of various
constraints where the executable memory can be located and this causes
additional obstacles for improvements of code allocation.

Start splitting code allocation from modules by introducing execmem_alloc()
and execmem_free() APIs.

Initially, execmem_alloc() is a wrapper for module_alloc() and
execmem_free() is a replacement of module_memfree() to allow updating all
call sites to use the new APIs.

Since architectures define different restrictions on placement,
permissions, alignment and other parameters for memory that can be used by
different subsystems that allocate executable memory, execmem_alloc() takes
a type argument, that will be used to identify the calling subsystem and to
allow architectures define parameters for ranges suitable for that
subsystem.

No functional changes.

Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

1 files changed, 57 insertions, 0 deletions

diff --git a/include/linux/execmem.h b/include/linux/execmem.h
new file mode 100644
index 000000000000..8eebc8ef66e7
--- /dev/null
+++ b/include/linux/execmem.h
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_EXECMEM_ALLOC_H
+#define _LINUX_EXECMEM_ALLOC_H
+
+#include <linux/types.h>
+#include <linux/moduleloader.h>
+
+/**
+ * enum execmem_type - types of executable memory ranges
+ *
+ * There are several subsystems that allocate executable memory.
+ * Architectures define different restrictions on placement,
+ * permissions, alignment and other parameters for memory that can be used
+ * by these subsystems.
+ * Types in this enum identify subsystems that allocate executable memory
+ * and let architectures define parameters for ranges suitable for
+ * allocations by each subsystem.
+ *
+ * @EXECMEM_DEFAULT: default parameters that would be used for types that
+ * are not explicitly defined.
+ * @EXECMEM_MODULE_TEXT: parameters for module text sections
+ * @EXECMEM_KPROBES: parameters for kprobes
+ * @EXECMEM_FTRACE: parameters for ftrace
+ * @EXECMEM_BPF: parameters for BPF
+ * @EXECMEM_TYPE_MAX:
+ */
+enum execmem_type {
+	EXECMEM_DEFAULT,
+	EXECMEM_MODULE_TEXT = EXECMEM_DEFAULT,
+	EXECMEM_KPROBES,
+	EXECMEM_FTRACE,
+	EXECMEM_BPF,
+	EXECMEM_TYPE_MAX,
+};
+
+/**
+ * execmem_alloc - allocate executable memory
+ * @type: type of the allocation
+ * @size: how many bytes of memory are required
+ *
+ * Allocates memory that will contain executable code, either generated or
+ * loaded from kernel modules.
+ *
+ * The memory will have protections defined by architecture for executable
+ * region of the @type.
+ *
+ * Return: a pointer to the allocated memory or %NULL
+ */
+void *execmem_alloc(enum execmem_type type, size_t size);
+
+/**
+ * execmem_free - free executable memory
+ * @ptr: pointer to the memory that should be freed
+ */
+void execmem_free(void *ptr);
+
+#endif /* _LINUX_EXECMEM_ALLOC_H */