codetag.c

// SPDX-License-Identifier: GPL-2.0-only
#include <linux/codetag.h>
#include <linux/idr.h>
#include <linux/kallsyms.h>
#include <linux/module.h>
#include <linux/seq_buf.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>

struct codetag_type {
	struct list_head link;
	unsigned int count;
	struct idr mod_idr;
	/*
	 * protects mod_idr, next_mod_seq,
	 * iter->mod_seq and cmod->mod_seq
	 */
	struct rw_semaphore mod_lock;
	struct codetag_type_desc desc;
	/* generates unique sequence number for module load */
	unsigned long next_mod_seq;
};

struct codetag_range {
	struct codetag *start;
	struct codetag *stop;
};

struct codetag_module {
	struct module *mod;
	struct codetag_range range;
	unsigned long mod_seq;
};

static DEFINE_MUTEX(codetag_lock);
static LIST_HEAD(codetag_types);

void codetag_lock_module_list(struct codetag_type *cttype, bool lock)
{
	if (lock)
		down_read(&cttype->mod_lock);
	else
		up_read(&cttype->mod_lock);
}

bool codetag_trylock_module_list(struct codetag_type *cttype)
{
	return down_read_trylock(&cttype->mod_lock) != 0;
}

struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype)
{
	struct codetag_iterator iter = {
		.cttype = cttype,
		.cmod = NULL,
		.mod_id = 0,
		.ct = NULL,
		.mod_seq = 0,
	};

	return iter;
}

static inline struct codetag *get_first_module_ct(struct codetag_module *cmod)
{
	return cmod->range.start < cmod->range.stop ? cmod->range.start : NULL;
}

static inline
struct codetag *get_next_module_ct(struct codetag_iterator *iter)
{
	struct codetag *res = (struct codetag *)
			((char *)iter->ct + iter->cttype->desc.tag_size);

	return res < iter->cmod->range.stop ? res : NULL;
}

struct codetag *codetag_next_ct(struct codetag_iterator *iter)
{
	struct codetag_type *cttype = iter->cttype;
	struct codetag_module *cmod;
	struct codetag *ct;

	lockdep_assert_held(&cttype->mod_lock);

	if (unlikely(idr_is_empty(&cttype->mod_idr)))
		return NULL;

	ct = NULL;
	while (true) {
		cmod = idr_find(&cttype->mod_idr, iter->mod_id);

		/* If module was removed move to the next one */
		if (!cmod)
			cmod = idr_get_next_ul(&cttype->mod_idr,
					       &iter->mod_id);

		/* Exit if no more modules */
		if (!cmod)
			break;

		if (!iter->cmod || iter->mod_seq != cmod->mod_seq) {
			iter->cmod = cmod;
			iter->mod_seq = cmod->mod_seq;
			ct = get_first_module_ct(cmod);
		} else {
			ct = get_next_module_ct(iter);
		}

		if (ct)
			break;

		iter->mod_id++;
	}

	iter->ct = ct;
	return ct;
}

void codetag_to_text(struct seq_buf *out, struct codetag *ct)
{
	if (ct->modname)
		seq_buf_printf(out, "%s:%u [%s] func:%s",
			       ct->filename, ct->lineno,
			       ct->modname, ct->function);
	else
		seq_buf_printf(out, "%s:%u func:%s",
			       ct->filename, ct->lineno, ct->function);
}

static inline size_t range_size(const struct codetag_type *cttype,
				const struct codetag_range *range)
{
	return ((char *)range->stop - (char *)range->start) /
			cttype->desc.tag_size;
}

static void *get_symbol(struct module *mod, const char *prefix, const char *name)
{
	DECLARE_SEQ_BUF(sb, KSYM_NAME_LEN);
	const char *buf;
	void *ret;

	seq_buf_printf(&sb, "%s%s", prefix, name);
	if (seq_buf_has_overflowed(&sb))
		return NULL;

	buf = seq_buf_str(&sb);
	preempt_disable();
	ret = mod ?
		(void *)find_kallsyms_symbol_value(mod, buf) :
		(void *)kallsyms_lookup_name(buf);
	preempt_enable();

	return ret;
}

static struct codetag_range get_section_range(struct module *mod,
					      const char *section)
{
	return (struct codetag_range) {
		get_symbol(mod, CODETAG_SECTION_START_PREFIX, section),
		get_symbol(mod, CODETAG_SECTION_STOP_PREFIX, section),
	};
}

static const char *get_mod_name(__maybe_unused struct module *mod)
{
#ifdef CONFIG_MODULES
	if (mod)
		return mod->name;
#endif
	return "(built-in)";
}

static int codetag_module_init(struct codetag_type *cttype, struct module *mod)
{
	struct codetag_range range;
	struct codetag_module *cmod;
	int mod_id;
	int err;

	range = get_section_range(mod, cttype->desc.section);
	if (!range.start || !range.stop) {
		pr_warn("Failed to load code tags of type %s from the module %s\n",
			cttype->desc.section, get_mod_name(mod));
		return -EINVAL;
	}

	/* Ignore empty ranges */
	if (range.start == range.stop)
		return 0;

	BUG_ON(range.start > range.stop);

	cmod = kmalloc(sizeof(*cmod), GFP_KERNEL);
	if (unlikely(!cmod))
		return -ENOMEM;

	cmod->mod = mod;
	cmod->range = range;

	down_write(&cttype->mod_lock);
	cmod->mod_seq = ++cttype->next_mod_seq;
	mod_id = idr_alloc(&cttype->mod_idr, cmod, 0, 0, GFP_KERNEL);
	if (mod_id >= 0) {
		if (cttype->desc.module_load) {
			err = cttype->desc.module_load(mod, range.start, range.stop);
			if (!err)
				cttype->count += range_size(cttype, &range);
			else
				idr_remove(&cttype->mod_idr, mod_id);
		} else {
			cttype->count += range_size(cttype, &range);
			err = 0;
		}
	} else {
		err = mod_id;
	}
	up_write(&cttype->mod_lock);

	if (err < 0) {
		kfree(cmod);
		return err;
	}

	return 0;
}

#ifdef CONFIG_MODULES
#define CODETAG_SECTION_PREFIX	".codetag."

/* Some codetag types need a separate module section */
bool codetag_needs_module_section(struct module *mod, const char *name,
				  unsigned long size)
{
	const char *type_name;
	struct codetag_type *cttype;
	bool ret = false;

	if (strncmp(name, CODETAG_SECTION_PREFIX, strlen(CODETAG_SECTION_PREFIX)))
		return false;

	type_name = name + strlen(CODETAG_SECTION_PREFIX);
	mutex_lock(&codetag_lock);
	list_for_each_entry(cttype, &codetag_types, link) {
		if (strcmp(type_name, cttype->desc.section) == 0) {
			if (!cttype->desc.needs_section_mem)
				break;

			down_write(&cttype->mod_lock);
			ret = cttype->desc.needs_section_mem(mod, size);
			up_write(&cttype->mod_lock);
			break;
		}
	}
	mutex_unlock(&codetag_lock);

	return ret;
}

void *codetag_alloc_module_section(struct module *mod, const char *name,
				   unsigned long size, unsigned int prepend,
				   unsigned long align)
{
	const char *type_name = name + strlen(CODETAG_SECTION_PREFIX);
	struct codetag_type *cttype;
	void *ret = ERR_PTR(-EINVAL);

	mutex_lock(&codetag_lock);
	list_for_each_entry(cttype, &codetag_types, link) {
		if (strcmp(type_name, cttype->desc.section) == 0) {
			if (WARN_ON(!cttype->desc.alloc_section_mem))
				break;

			down_write(&cttype->mod_lock);
			ret = cttype->desc.alloc_section_mem(mod, size, prepend, align);
			up_write(&cttype->mod_lock);
			break;
		}
	}
	mutex_unlock(&codetag_lock);

	return ret;
}

void codetag_free_module_sections(struct module *mod)
{
	struct codetag_type *cttype;

	mutex_lock(&codetag_lock);
	list_for_each_entry(cttype, &codetag_types, link) {
		if (!cttype->desc.free_section_mem)
			continue;

		down_write(&cttype->mod_lock);
		cttype->desc.free_section_mem(mod, false);
		up_write(&cttype->mod_lock);
	}
	mutex_unlock(&codetag_lock);
}

void codetag_module_replaced(struct module *mod, struct module *new_mod)
{
	struct codetag_type *cttype;

	mutex_lock(&codetag_lock);
	list_for_each_entry(cttype, &codetag_types, link) {
		if (!cttype->desc.module_replaced)
			continue;

		down_write(&cttype->mod_lock);
		cttype->desc.module_replaced(mod, new_mod);
		up_write(&cttype->mod_lock);
	}
	mutex_unlock(&codetag_lock);
}

int codetag_load_module(struct module *mod)
{
	struct codetag_type *cttype;
	int ret = 0;

	if (!mod)
		return 0;

	mutex_lock(&codetag_lock);
	list_for_each_entry(cttype, &codetag_types, link) {
		ret = codetag_module_init(cttype, mod);
		if (ret)
			break;
	}
	mutex_unlock(&codetag_lock);

	return ret;
}

void codetag_unload_module(struct module *mod)
{
	struct codetag_type *cttype;

	if (!mod)
		return;

	/* await any module's kfree_rcu() operations to complete */
	kvfree_rcu_barrier();

	mutex_lock(&codetag_lock);
	list_for_each_entry(cttype, &codetag_types, link) {
		struct codetag_module *found = NULL;
		struct codetag_module *cmod;
		unsigned long mod_id, tmp;

		down_write(&cttype->mod_lock);
		idr_for_each_entry_ul(&cttype->mod_idr, cmod, tmp, mod_id) {
			if (cmod->mod && cmod->mod == mod) {
				found = cmod;
				break;
			}
		}
		if (found) {
			if (cttype->desc.module_unload)
				cttype->desc.module_unload(cmod->mod,
					cmod->range.start, cmod->range.stop);

			cttype->count -= range_size(cttype, &cmod->range);
			idr_remove(&cttype->mod_idr, mod_id);
			kfree(cmod);
		}
		up_write(&cttype->mod_lock);
		if (found && cttype->desc.free_section_mem)
			cttype->desc.free_section_mem(mod, true);
	}
	mutex_unlock(&codetag_lock);
}
#endif /* CONFIG_MODULES */

struct codetag_type *
codetag_register_type(const struct codetag_type_desc *desc)
{
	struct codetag_type *cttype;
	int err;

	BUG_ON(desc->tag_size <= 0);

	cttype = kzalloc(sizeof(*cttype), GFP_KERNEL);
	if (unlikely(!cttype))
		return ERR_PTR(-ENOMEM);

	cttype->desc = *desc;
	idr_init(&cttype->mod_idr);
	init_rwsem(&cttype->mod_lock);

	err = codetag_module_init(cttype, NULL);
	if (unlikely(err)) {
		kfree(cttype);
		return ERR_PTR(err);
	}

	mutex_lock(&codetag_lock);
	list_add_tail(&cttype->link, &codetag_types);
	mutex_unlock(&codetag_lock);

	return cttype;
}