kernel/extable.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* Rewritten by Rusty Russell, on the backs of many others...
   Copyright (C) 2001 Rusty Russell, 2002 Rusty Russell IBM.

*/
#include <linux/elf.h>
#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 notrace core_kernel_text(unsigned long addr)
{
	if (is_kernel_text(addr))
		return 1;

	if (system_state < SYSTEM_FREEING_INITMEM &&
	    is_kernel_inittext(addr))
		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 (is_kernel_inittext(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)
		ct_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)
		ct_nmi_exit();

	return ret;
}

/*
 * On some architectures (PPC64, IA64, PARISC) 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.
 */
#ifdef CONFIG_HAVE_FUNCTION_DESCRIPTORS
void *dereference_function_descriptor(void *ptr)
{
	func_desc_t *desc = ptr;
	void *p;

	if (!get_kernel_nofault(p, (void *)&desc->addr))
		ptr = p;
	return ptr;
}
EXPORT_SYMBOL_GPL(dereference_function_descriptor);

void *dereference_kernel_function_descriptor(void *ptr)
{
	if (ptr < (void *)__start_opd || ptr >= (void *)__end_opd)
		return ptr;

	return dereference_function_descriptor(ptr);
}
#endif

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);
}