livepatch: kernel: add support for live patching

This commit introduces code for the live patching core.  It implements
an ftrace-based mechanism and kernel interface for doing live patching
of kernel and kernel module functions.

It represents the greatest common functionality set between kpatch and
kgraft and can accept patches built using either method.

This first version does not implement any consistency mechanism that
ensures that old and new code do not run together.  In practice, ~90% of
CVEs are safe to apply in this way, since they simply add a conditional
check.  However, any function change that can not execute safely with
the old version of the function can _not_ be safely applied in this
version.

[ jkosina@suse.cz: due to the number of contributions that got folded into
  this original patch from Seth Jennings, add SUSE's copyright as well, as
  discussed via e-mail ]

Signed-off-by: Seth Jennings <sjenning@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.cz>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 133 insertions, 0 deletions

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
new file mode 100644
index 000000000000..950bc615842f
--- /dev/null
+++ b/include/linux/livepatch.h
@@ -0,0 +1,133 @@
+/*
+ * livepatch.h - Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ * Copyright (C) 2014 SUSE
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _LINUX_LIVEPATCH_H_
+#define _LINUX_LIVEPATCH_H_
+
+#include <linux/module.h>
+#include <linux/ftrace.h>
+
+#if IS_ENABLED(CONFIG_LIVE_PATCHING)
+
+#include <asm/livepatch.h>
+
+enum klp_state {
+        KLP_DISABLED,
+        KLP_ENABLED
+};
+
+/**
+ * struct klp_func - function structure for live patching
+ * @old_name:   name of the function to be patched
+ * @new_func:   pointer to the patched function code
+ * @old_addr:   a hint conveying at what address the old function
+ *              can be found (optional, vmlinux patches only)
+ * @kobj:       kobject for sysfs resources
+ * @fops:       ftrace operations structure
+ * @state:      tracks function-level patch application state
+ */
+struct klp_func {
+        /* external */
+        const char *old_name;
+        void *new_func;
+        /*
+         * The old_addr field is optional and can be used to resolve
+         * duplicate symbol names in the vmlinux object.  If this
+         * information is not present, the symbol is located by name
+         * with kallsyms. If the name is not unique and old_addr is
+         * not provided, the patch application fails as there is no
+         * way to resolve the ambiguity.
+         */
+        unsigned long old_addr;
+
+        /* internal */
+        struct kobject kobj;
+        struct ftrace_ops *fops;
+        enum klp_state state;
+};
+
+/**
+ * struct klp_reloc - relocation structure for live patching
+ * @loc:        address where the relocation will be written
+ * @val:        address of the referenced symbol (optional,
+ *              vmlinux patches only)
+ * @type:       ELF relocation type
+ * @name:       name of the referenced symbol (for lookup/verification)
+ * @addend:     offset from the referenced symbol
+ * @external:   symbol is either exported or within the live patch module itself
+ */
+struct klp_reloc {
+        unsigned long loc;
+        unsigned long val;
+        unsigned long type;
+        const char *name;
+        int addend;
+        int external;
+};
+
+/**
+ * struct klp_object - kernel object structure for live patching
+ * @name:       module name (or NULL for vmlinux)
+ * @relocs:     relocation entries to be applied at load time
+ * @funcs:      function entries for functions to be patched in the object
+ * @kobj:       kobject for sysfs resources
+ * @mod:        kernel module associated with the patched object
+ *              (NULL for vmlinux)
+ * @state:      tracks object-level patch application state
+ */
+struct klp_object {
+        /* external */
+        const char *name;
+        struct klp_reloc *relocs;
+        struct klp_func *funcs;
+
+        /* internal */
+        struct kobject *kobj;
+        struct module *mod;
+        enum klp_state state;
+};
+
+/**
+ * struct klp_patch - patch structure for live patching
+ * @mod:        reference to the live patch module
+ * @objs:       object entries for kernel objects to be patched
+ * @list:       list node for global list of registered patches
+ * @kobj:       kobject for sysfs resources
+ * @state:      tracks patch-level application state
+ */
+struct klp_patch {
+        /* external */
+        struct module *mod;
+        struct klp_object *objs;
+
+        /* internal */
+        struct list_head list;
+        struct kobject kobj;
+        enum klp_state state;
+};
+
+extern int klp_register_patch(struct klp_patch *);
+extern int klp_unregister_patch(struct klp_patch *);
+extern int klp_enable_patch(struct klp_patch *);
+extern int klp_disable_patch(struct klp_patch *);
+
+#endif /* CONFIG_LIVE_PATCHING */
+
+#endif /* _LINUX_LIVEPATCH_H_ */