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authorJosh Poimboeuf <jpoimboe@redhat.com>2015-01-20 09:26:19 -0600
committerJiri Kosina <jkosina@suse.cz>2015-01-20 20:09:41 +0100
commit3c33f5b99d688deafd21d4a770303691c7c3a320 (patch)
tree1b133a30910364c15190202616f65c08d306f55e /kernel/livepatch
parent83a90bb1345767f0cb96d242fd8b9db44b2b0e17 (diff)
downloadlinux-sh-3c33f5b99d688deafd21d4a770303691c7c3a320.tar.gz
livepatch: support for repatching a function
Add support for patching a function multiple times. If multiple patches affect a function, the function in the most recently enabled patch "wins". This enables a cumulative patch upgrade path, where each patch is a superset of previous patches. This requires restructuring the data a little bit. With the current design, where each klp_func struct has its own ftrace_ops, we'd have to unregister the old ops and then register the new ops, because FTRACE_OPS_FL_IPMODIFY prevents us from having two ops registered for the same function at the same time. That would leave a regression window where the function isn't patched at all (not good for a patch upgrade path). This patch replaces the per-klp_func ftrace_ops with a global klp_ops list, with one ftrace_ops per original function. A single ftrace_ops is shared between all klp_funcs which have the same old_addr. This allows the switch between function versions to happen instantaneously by updating the klp_ops struct's func_stack list. The winner is the klp_func at the top of the func_stack (front of the list). [ jkosina@suse.cz: turn WARN_ON() into WARN_ON_ONCE() in ftrace handler to avoid storm in pathological cases ] Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Reviewed-by: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Diffstat (limited to 'kernel/livepatch')
-rw-r--r--kernel/livepatch/core.c170
1 files changed, 119 insertions, 51 deletions
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 2401e7f955d3..bc05d390ce85 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -29,17 +29,53 @@
#include <linux/kallsyms.h>
#include <linux/livepatch.h>
-/*
- * The klp_mutex protects the klp_patches list and state transitions of any
- * structure reachable from the patches list. References to any structure must
- * be obtained under mutex protection.
+/**
+ * struct klp_ops - structure for tracking registered ftrace ops structs
+ *
+ * A single ftrace_ops is shared between all enabled replacement functions
+ * (klp_func structs) which have the same old_addr. This allows the switch
+ * between function versions to happen instantaneously by updating the klp_ops
+ * struct's func_stack list. The winner is the klp_func at the top of the
+ * func_stack (front of the list).
+ *
+ * @node: node for the global klp_ops list
+ * @func_stack: list head for the stack of klp_func's (active func is on top)
+ * @fops: registered ftrace ops struct
*/
+struct klp_ops {
+ struct list_head node;
+ struct list_head func_stack;
+ struct ftrace_ops fops;
+};
+/*
+ * The klp_mutex protects the global lists and state transitions of any
+ * structure reachable from them. References to any structure must be obtained
+ * under mutex protection (except in klp_ftrace_handler(), which uses RCU to
+ * ensure it gets consistent data).
+ */
static DEFINE_MUTEX(klp_mutex);
+
static LIST_HEAD(klp_patches);
+static LIST_HEAD(klp_ops);
static struct kobject *klp_root_kobj;
+static struct klp_ops *klp_find_ops(unsigned long old_addr)
+{
+ struct klp_ops *ops;
+ struct klp_func *func;
+
+ list_for_each_entry(ops, &klp_ops, node) {
+ func = list_first_entry(&ops->func_stack, struct klp_func,
+ stack_node);
+ if (func->old_addr == old_addr)
+ return ops;
+ }
+
+ return NULL;
+}
+
static bool klp_is_module(struct klp_object *obj)
{
return obj->name;
@@ -267,16 +303,28 @@ static int klp_write_object_relocations(struct module *pmod,
static void notrace klp_ftrace_handler(unsigned long ip,
unsigned long parent_ip,
- struct ftrace_ops *ops,
+ struct ftrace_ops *fops,
struct pt_regs *regs)
{
- struct klp_func *func = ops->private;
+ struct klp_ops *ops;
+ struct klp_func *func;
+
+ ops = container_of(fops, struct klp_ops, fops);
+
+ rcu_read_lock();
+ func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
+ stack_node);
+ rcu_read_unlock();
+
+ if (WARN_ON_ONCE(!func))
+ return;
klp_arch_set_pc(regs, (unsigned long)func->new_func);
}
static int klp_disable_func(struct klp_func *func)
{
+ struct klp_ops *ops;
int ret;
if (WARN_ON(func->state != KLP_ENABLED))
@@ -285,16 +333,28 @@ static int klp_disable_func(struct klp_func *func)
if (WARN_ON(!func->old_addr))
return -EINVAL;
- ret = unregister_ftrace_function(func->fops);
- if (ret) {
- pr_err("failed to unregister ftrace handler for function '%s' (%d)\n",
- func->old_name, ret);
- return ret;
- }
+ ops = klp_find_ops(func->old_addr);
+ if (WARN_ON(!ops))
+ return -EINVAL;
- ret = ftrace_set_filter_ip(func->fops, func->old_addr, 1, 0);
- if (ret)
- pr_warn("function unregister succeeded but failed to clear the filter\n");
+ if (list_is_singular(&ops->func_stack)) {
+ ret = unregister_ftrace_function(&ops->fops);
+ if (ret) {
+ pr_err("failed to unregister ftrace handler for function '%s' (%d)\n",
+ func->old_name, ret);
+ return ret;
+ }
+
+ ret = ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0);
+ if (ret)
+ pr_warn("function unregister succeeded but failed to clear the filter\n");
+
+ list_del_rcu(&func->stack_node);
+ list_del(&ops->node);
+ kfree(ops);
+ } else {
+ list_del_rcu(&func->stack_node);
+ }
func->state = KLP_DISABLED;
@@ -303,6 +363,7 @@ static int klp_disable_func(struct klp_func *func)
static int klp_enable_func(struct klp_func *func)
{
+ struct klp_ops *ops;
int ret;
if (WARN_ON(!func->old_addr))
@@ -311,22 +372,50 @@ static int klp_enable_func(struct klp_func *func)
if (WARN_ON(func->state != KLP_DISABLED))
return -EINVAL;
- ret = ftrace_set_filter_ip(func->fops, func->old_addr, 0, 0);
- if (ret) {
- pr_err("failed to set ftrace filter for function '%s' (%d)\n",
- func->old_name, ret);
- return ret;
- }
+ ops = klp_find_ops(func->old_addr);
+ if (!ops) {
+ ops = kzalloc(sizeof(*ops), GFP_KERNEL);
+ if (!ops)
+ return -ENOMEM;
+
+ ops->fops.func = klp_ftrace_handler;
+ ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
+ FTRACE_OPS_FL_DYNAMIC |
+ FTRACE_OPS_FL_IPMODIFY;
+
+ list_add(&ops->node, &klp_ops);
+
+ INIT_LIST_HEAD(&ops->func_stack);
+ list_add_rcu(&func->stack_node, &ops->func_stack);
+
+ ret = ftrace_set_filter_ip(&ops->fops, func->old_addr, 0, 0);
+ if (ret) {
+ pr_err("failed to set ftrace filter for function '%s' (%d)\n",
+ func->old_name, ret);
+ goto err;
+ }
+
+ ret = register_ftrace_function(&ops->fops);
+ if (ret) {
+ pr_err("failed to register ftrace handler for function '%s' (%d)\n",
+ func->old_name, ret);
+ ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0);
+ goto err;
+ }
+
- ret = register_ftrace_function(func->fops);
- if (ret) {
- pr_err("failed to register ftrace handler for function '%s' (%d)\n",
- func->old_name, ret);
- ftrace_set_filter_ip(func->fops, func->old_addr, 1, 0);
} else {
- func->state = KLP_ENABLED;
+ list_add_rcu(&func->stack_node, &ops->func_stack);
}
+ func->state = KLP_ENABLED;
+
+ return ret;
+
+err:
+ list_del_rcu(&func->stack_node);
+ list_del(&ops->node);
+ kfree(ops);
return ret;
}
@@ -582,10 +671,6 @@ static struct kobj_type klp_ktype_patch = {
static void klp_kobj_release_func(struct kobject *kobj)
{
- struct klp_func *func;
-
- func = container_of(kobj, struct klp_func, kobj);
- kfree(func->fops);
}
static struct kobj_type klp_ktype_func = {
@@ -642,28 +727,11 @@ static void klp_free_patch(struct klp_patch *patch)
static int klp_init_func(struct klp_object *obj, struct klp_func *func)
{
- struct ftrace_ops *ops;
- int ret;
-
- ops = kzalloc(sizeof(*ops), GFP_KERNEL);
- if (!ops)
- return -ENOMEM;
-
- ops->private = func;
- ops->func = klp_ftrace_handler;
- ops->flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_DYNAMIC |
- FTRACE_OPS_FL_IPMODIFY;
- func->fops = ops;
+ INIT_LIST_HEAD(&func->stack_node);
func->state = KLP_DISABLED;
- ret = kobject_init_and_add(&func->kobj, &klp_ktype_func,
- obj->kobj, func->old_name);
- if (ret) {
- kfree(func->fops);
- return ret;
- }
-
- return 0;
+ return kobject_init_and_add(&func->kobj, &klp_ktype_func,
+ obj->kobj, func->old_name);
}
/* parts of the initialization that is done only when the object is loaded */