修改kernel text 段为RW

kernel的text段是RO的，如果想改变text段为RW，可以关掉CONFIG_STRICT_KERNEL_RWX 和 CONFIG_STRICT_MODULE_RWX 
这两个配置项
#if defined(CONFIG_STRICT_KERNEL_RWX) || defined(CONFIG_STRICT_MODULE_RWX)
bool rodata_enabled __ro_after_init = true;
static int __init set_debug_rodata(char *str)
{
	return strtobool(str, &rodata_enabled);
}
__setup("rodata=", set_debug_rodata);
#endif
也可以在命令行加rodata=false。
命令行设置rodata=false，解析函数set_debug_rodata，会让rodata_enabled等于false
static void __init map_kernel(pgd_t *pgdp)
{
	static struct vm_struct vmlinux_text, vmlinux_rodata, vmlinux_inittext,
				vmlinux_initdata, vmlinux_data;

#这里的rodata_enabled 为false的话，则text_prot 应该等于PAGE_KERNEL_EXEC
	pgprot_t text_prot = rodata_enabled ? PAGE_KERNEL_ROX : PAGE_KERNEL_EXEC;

	/*
	 * If we have a CPU that supports BTI and a kernel built for
	 * BTI then mark the kernel executable text as guarded pages
	 * now so we don't have to rewrite the page tables later.
	 */
	if (arm64_early_this_cpu_has_bti())
		text_prot = __pgprot_modify(text_prot, PTE_GP, PTE_GP);

	/*
	 * Only rodata will be remapped with different permissions later on,
	 * all other segments are allowed to use contiguous mappings.
	 */
#按照PAGE_KERNEL_EXEC 来映射text段，所以text段就是RW的
	map_kernel_segment(pgdp, _text, _etext, text_prot, &vmlinux_text, 0,
			   VM_NO_GUARD);
	map_kernel_segment(pgdp, __start_rodata, __inittext_begin, PAGE_KERNEL,
			   &vmlinux_rodata, NO_CONT_MAPPINGS, VM_NO_GUARD);
	map_kernel_segment(pgdp, __inittext_begin, __inittext_end, text_prot,
			   &vmlinux_inittext, 0, VM_NO_GUARD);
	map_kernel_segment(pgdp, __initdata_begin, __initdata_end, PAGE_KERNEL,
			   &vmlinux_initdata, 0, VM_NO_GUARD);
	map_kernel_segment(pgdp, _data, _end, PAGE_KERNEL, &vmlinux_data, 0, 0);
}