derone (undo "permanent" read-only kernel protections)

derone.c

#include <linux/module.h>
#include <linux/kallsyms.h>

#define MODULE_NAME "derone"

static int __init derone_init(void)
{
	printk(KERN_INFO "derone_init\n");

	typedef int set_memory_fn_t(u64, int);
	set_memory_fn_t *set_memory_ro =
		(set_memory_fn_t *)kallsyms_lookup_name("set_memory_ro");
	set_memory_fn_t *set_memory_rw =
		(set_memory_fn_t *)kallsyms_lookup_name("set_memory_rw");

	printk(KERN_INFO "derone: set_memory_ro=0x%llx set_memory_rw=0x%llx\n",
	       (u64)set_memory_ro, (u64)set_memory_rw);

	void *kaslr = (void *)set_memory_ro - SYSTEM_MAP_set_memory_ro;
	_Atomic u64 *
		x86_amd_ls_cfg_base_ptr = // kallsyms_lookup_name("x86_amd_ls_cfg_base");
		kaslr + SYSTEM_MAP_x86_amd_ls_cfg_base;
	_Atomic int *
		kernel_set_to_readonly_ptr = // kallsyms_lookup_name("kernel_set_to_readonly");
		kaslr + SYSTEM_MAP_kernel_set_to_readonly;

	printk(KERN_INFO
	       "derone: x86_amd_ls_cfg_base addr=0x%llx value=0x%llx\n",
	       (u64)x86_amd_ls_cfg_base_ptr, *x86_amd_ls_cfg_base_ptr);
	printk(KERN_INFO
	       "derone: kernel_set_to_readonly addr=0x%llx value=%d\n",
	       (u64)kernel_set_to_readonly_ptr, *kernel_set_to_readonly_ptr);

	printk(KERN_INFO
	       "derone: attempting to unprotect x86_amd_ls_cfg_base\n");

	*kernel_set_to_readonly_ptr = 0;
	int result = set_memory_rw((u64)x86_amd_ls_cfg_base_ptr, 1);
	*kernel_set_to_readonly_ptr = 1;

	printk(KERN_INFO "derone: set_memory_rw(0x%llx, 1) = %d\n",
	       (u64)x86_amd_ls_cfg_base_ptr, result);

	*x86_amd_ls_cfg_base_ptr |= 0x40000000000000;

	printk(KERN_INFO "derone: set_memory_ro(0x%llx, 1) = %d\n",
	       (u64)x86_amd_ls_cfg_base_ptr,
	       set_memory_ro((u64)x86_amd_ls_cfg_base_ptr, 1));

	printk(KERN_INFO
	       "derone: x86_amd_ls_cfg_base addr=0x%llx value=0x%llx\n",
	       (u64)x86_amd_ls_cfg_base_ptr, *x86_amd_ls_cfg_base_ptr);

	printk(KERN_INFO "derone_init: done\n");

	return 0;
}
static void __exit derone_cleanup(void)
{
	printk(KERN_INFO "derone_cleanup\n");
}
module_init(derone_init);
module_exit(derone_cleanup);
MODULE_LICENSE("GPL");

Kbuild

SYSTEM_MAP ?= /run/booted-system/kernel-modules/System.map
CFLAGS_derone.o = \
	-D SYSTEM_MAP_set_memory_ro=0x$(shell grep set_memory_ro $(SYSTEM_MAP) | sed 's/ .*//') \
	-D SYSTEM_MAP_x86_amd_ls_cfg_base=0x$(shell grep x86_amd_ls_cfg_base $(SYSTEM_MAP) | sed 's/ .*//') \
	-D SYSTEM_MAP_kernel_set_to_readonly=0x$(shell grep kernel_set_to_readonly $(SYSTEM_MAP) | sed 's/ .*//')
obj-m += derone.o

Why are the kallsyms_lookup_name commented for x86_amd_ls_cfg_base and kernel_set_to_readonly? They do appear in /proc/kallsyms here, I'd expect kallsyms_lookup_name to work. As far as I can tell, it works here.

Oops torvalds/linux@0bd476e

I didn't see your comments here, sorry. /proc/kallsyms doesn't contain global variables on my 5.4.49, maybe it's a NixOS thing?
Ah it seems to be CONFIG_KALLSYMS_ALL that's missing, and which would enable global variables as well:

$ zgrep KALLSYMS /proc/config.gz
CONFIG_KALLSYMS=y
# CONFIG_KALLSYMS_ALL is not set
CONFIG_KALLSYMS_ABSOLUTE_PERCPU=y
CONFIG_KALLSYMS_BASE_RELATIVE=y