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276 lines
6.4 KiB
276 lines
6.4 KiB
/*
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* patch.c - livepatch patching functions
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*
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* Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
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* Copyright (C) 2014 SUSE
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* Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/livepatch.h>
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#include <linux/list.h>
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#include <linux/ftrace.h>
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#include <linux/rculist.h>
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#include <linux/slab.h>
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#include <linux/bug.h>
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#include <linux/printk.h>
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#include "patch.h"
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#include "transition.h"
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static LIST_HEAD(klp_ops);
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struct klp_ops *klp_find_ops(unsigned long old_addr)
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{
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struct klp_ops *ops;
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struct klp_func *func;
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list_for_each_entry(ops, &klp_ops, node) {
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func = list_first_entry(&ops->func_stack, struct klp_func,
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stack_node);
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if (func->old_addr == old_addr)
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return ops;
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}
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return NULL;
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}
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static void notrace klp_ftrace_handler(unsigned long ip,
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unsigned long parent_ip,
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struct ftrace_ops *fops,
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struct pt_regs *regs)
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{
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struct klp_ops *ops;
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struct klp_func *func;
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int patch_state;
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ops = container_of(fops, struct klp_ops, fops);
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/*
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* A variant of synchronize_sched() is used to allow patching functions
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* where RCU is not watching, see klp_synchronize_transition().
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*/
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preempt_disable_notrace();
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func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
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stack_node);
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/*
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* func should never be NULL because preemption should be disabled here
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* and unregister_ftrace_function() does the equivalent of a
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* synchronize_sched() before the func_stack removal.
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*/
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if (WARN_ON_ONCE(!func))
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goto unlock;
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/*
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* In the enable path, enforce the order of the ops->func_stack and
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* func->transition reads. The corresponding write barrier is in
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* __klp_enable_patch().
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*
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* (Note that this barrier technically isn't needed in the disable
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* path. In the rare case where klp_update_patch_state() runs before
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* this handler, its TIF_PATCH_PENDING read and this func->transition
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* read need to be ordered. But klp_update_patch_state() already
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* enforces that.)
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*/
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smp_rmb();
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if (unlikely(func->transition)) {
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/*
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* Enforce the order of the func->transition and
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* current->patch_state reads. Otherwise we could read an
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* out-of-date task state and pick the wrong function. The
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* corresponding write barrier is in klp_init_transition().
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*/
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smp_rmb();
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patch_state = current->patch_state;
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WARN_ON_ONCE(patch_state == KLP_UNDEFINED);
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if (patch_state == KLP_UNPATCHED) {
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/*
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* Use the previously patched version of the function.
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* If no previous patches exist, continue with the
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* original function.
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*/
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func = list_entry_rcu(func->stack_node.next,
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struct klp_func, stack_node);
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if (&func->stack_node == &ops->func_stack)
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goto unlock;
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}
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}
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klp_arch_set_pc(regs, (unsigned long)func->new_func);
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unlock:
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preempt_enable_notrace();
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}
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/*
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* Convert a function address into the appropriate ftrace location.
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*
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* Usually this is just the address of the function, but on some architectures
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* it's more complicated so allow them to provide a custom behaviour.
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*/
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#ifndef klp_get_ftrace_location
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static unsigned long klp_get_ftrace_location(unsigned long faddr)
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{
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return faddr;
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}
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#endif
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static void klp_unpatch_func(struct klp_func *func)
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{
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struct klp_ops *ops;
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if (WARN_ON(!func->patched))
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return;
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if (WARN_ON(!func->old_addr))
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return;
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ops = klp_find_ops(func->old_addr);
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if (WARN_ON(!ops))
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return;
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if (list_is_singular(&ops->func_stack)) {
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unsigned long ftrace_loc;
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ftrace_loc = klp_get_ftrace_location(func->old_addr);
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if (WARN_ON(!ftrace_loc))
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return;
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WARN_ON(unregister_ftrace_function(&ops->fops));
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WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));
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list_del_rcu(&func->stack_node);
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list_del(&ops->node);
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kfree(ops);
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} else {
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list_del_rcu(&func->stack_node);
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}
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func->patched = false;
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}
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static int klp_patch_func(struct klp_func *func)
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{
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struct klp_ops *ops;
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int ret;
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if (WARN_ON(!func->old_addr))
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return -EINVAL;
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if (WARN_ON(func->patched))
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return -EINVAL;
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ops = klp_find_ops(func->old_addr);
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if (!ops) {
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unsigned long ftrace_loc;
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ftrace_loc = klp_get_ftrace_location(func->old_addr);
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if (!ftrace_loc) {
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pr_err("failed to find location for function '%s'\n",
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func->old_name);
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return -EINVAL;
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}
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ops = kzalloc(sizeof(*ops), GFP_KERNEL);
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if (!ops)
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return -ENOMEM;
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ops->fops.func = klp_ftrace_handler;
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ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
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FTRACE_OPS_FL_DYNAMIC |
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FTRACE_OPS_FL_IPMODIFY;
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list_add(&ops->node, &klp_ops);
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INIT_LIST_HEAD(&ops->func_stack);
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list_add_rcu(&func->stack_node, &ops->func_stack);
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ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);
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if (ret) {
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pr_err("failed to set ftrace filter for function '%s' (%d)\n",
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func->old_name, ret);
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goto err;
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}
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ret = register_ftrace_function(&ops->fops);
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if (ret) {
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pr_err("failed to register ftrace handler for function '%s' (%d)\n",
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func->old_name, ret);
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ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);
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goto err;
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}
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} else {
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list_add_rcu(&func->stack_node, &ops->func_stack);
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}
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func->patched = true;
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return 0;
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err:
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list_del_rcu(&func->stack_node);
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list_del(&ops->node);
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kfree(ops);
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return ret;
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}
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void klp_unpatch_object(struct klp_object *obj)
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{
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struct klp_func *func;
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klp_for_each_func(obj, func)
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if (func->patched)
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klp_unpatch_func(func);
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obj->patched = false;
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}
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int klp_patch_object(struct klp_object *obj)
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{
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struct klp_func *func;
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int ret;
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if (WARN_ON(obj->patched))
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return -EINVAL;
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klp_for_each_func(obj, func) {
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ret = klp_patch_func(func);
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if (ret) {
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klp_unpatch_object(obj);
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return ret;
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}
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}
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obj->patched = true;
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return 0;
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}
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void klp_unpatch_objects(struct klp_patch *patch)
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{
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struct klp_object *obj;
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klp_for_each_object(patch, obj)
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if (obj->patched)
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klp_unpatch_object(obj);
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}
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