/* Rewritten by Rusty Russell, on the backs of many others...
   Copyright (C) 2001 Rusty Russell, 2002 Rusty Russell IBM.

    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, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/
#include <linux/ftrace.h>
#include <linux/memory.h>
#include <linux/extable.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/init.h>
#include <linux/kprobes.h>
#include <linux/filter.h>

#include <asm/sections.h>
#include <linux/uaccess.h>

/*
 * mutex protecting text section modification (dynamic code patching).
 * some users need to sleep (allocating memory...) while they hold this lock.
 *
 * Note: Also protects SMP-alternatives modification on x86.
 *
 * NOT exported to modules - patching kernel text is a really delicate matter.
 */
DEFINE_MUTEX(text_mutex);

extern struct exception_table_entry __start___ex_table[];
extern struct exception_table_entry __stop___ex_table[];

/* Cleared by build time tools if the table is already sorted. */
u32 __initdata __visible main_extable_sort_needed = 1;

/* Sort the kernel's built-in exception table */
void __init sort_main_extable(void)
{
        if (main_extable_sort_needed && __stop___ex_table > __start___ex_table) {
                pr_notice("Sorting __ex_table...\n");
                sort_extable(__start___ex_table, __stop___ex_table);
        }
}

/* Given an address, look for it in the kernel exception table */
const
struct exception_table_entry *search_kernel_exception_table(unsigned long addr)
{
        return search_extable(__start___ex_table,
                              __stop___ex_table - __start___ex_table, addr);
}

/* Given an address, look for it in the exception tables. */
const struct exception_table_entry *search_exception_tables(unsigned long addr)
{
        const struct exception_table_entry *e;

        e = search_kernel_exception_table(addr);
        if (!e)
                e = search_module_extables(addr);
        if (!e)
                e = search_bpf_extables(addr);
        return e;
}

int init_kernel_text(unsigned long addr)
{
        if (addr >= (unsigned long)_sinittext &&
            addr < (unsigned long)_einittext)
                return 1;
        return 0;
}

int notrace core_kernel_text(unsigned long addr)
{
        if (addr >= (unsigned long)_stext &&
            addr < (unsigned long)_etext)
                return 1;

        if (system_state < SYSTEM_RUNNING &&
            init_kernel_text(addr))
                return 1;
        return 0;
}

/**
 * core_kernel_data - tell if addr points to kernel data
 * @addr: address to test
 *
 * Returns true if @addr passed in is from the core kernel data
 * section.
 *
 * Note: On some archs it may return true for core RODATA, and false
 *  for others. But will always be true for core RW data.
 */
int core_kernel_data(unsigned long addr)
{
        if (addr >= (unsigned long)_sdata &&
            addr < (unsigned long)_edata)
                return 1;
        return 0;
}

int __kernel_text_address(unsigned long addr)
{
        if (kernel_text_address(addr))
                return 1;
        /*
         * There might be init symbols in saved stacktraces.
         * Give those symbols a chance to be printed in
         * backtraces (such as lockdep traces).
         *
         * Since we are after the module-symbols check, there's
         * no danger of address overlap:
         */
        if (init_kernel_text(addr))
                return 1;
        return 0;
}

int kernel_text_address(unsigned long addr)
{
        bool no_rcu;
        int ret = 1;

        if (core_kernel_text(addr))
                return 1;

        /*
         * If a stack dump happens while RCU is not watching, then
         * RCU needs to be notified that it requires to start
         * watching again. This can happen either by tracing that
         * triggers a stack trace, or a WARN() that happens during
         * coming back from idle, or cpu on or offlining.
         *
         * is_module_text_address() as well as the kprobe slots,
         * is_bpf_text_address() and is_bpf_image_address require
         * RCU to be watching.
         */
        no_rcu = !rcu_is_watching();

        /* Treat this like an NMI as it can happen anywhere */
        if (no_rcu)
                rcu_nmi_enter();

        if (is_module_text_address(addr))
                goto out;
        if (is_ftrace_trampoline(addr))
                goto out;
        if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr))
                goto out;
        if (is_bpf_text_address(addr))
                goto out;
        ret = 0;
out:
        if (no_rcu)
                rcu_nmi_exit();

        return ret;
}

/*
 * On some architectures (PPC64, IA64) function pointers
 * are actually only tokens to some data that then holds the
 * real function address. As a result, to find if a function
 * pointer is part of the kernel text, we need to do some
 * special dereferencing first.
 */
int func_ptr_is_kernel_text(void *ptr)
{
        unsigned long addr;
        addr = (unsigned long) dereference_function_descriptor(ptr);
        if (core_kernel_text(addr))
                return 1;
        return is_module_text_address(addr);
}