[RFC PATCH v2 4/7] tracing/user_events: Move pages/locks into groups to prepare for namespaces

From: Beau Belgrave
Date: Thu Jul 28 2022 - 19:53:17 EST

In order to enable namespaces or any sort of isolation within
user_events the register lock and pages need to be broken up into
groups. Each event and file now has a group pointer which stores the
actual pages to map, lookup data and synchronization objects.

Signed-off-by: Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx>
---
kernel/trace/trace_events_user.c | 381 ++++++++++++++++++++++++-------
1 file changed, 304 insertions(+), 77 deletions(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index fd8ea555437a..44f9efd58af5 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -69,11 +69,23 @@
#define EVENT_STATUS_PERF BIT(1)
#define EVENT_STATUS_OTHER BIT(7)

-static char *register_page_data;
+struct user_event_group {
+ struct page *pages;
+ char *register_page_data;
+ char *system_name;
+ struct dentry *status_file;
+ struct dentry *data_file;
+ struct hlist_node node;
+ struct mutex reg_mutex;
+ DECLARE_HASHTABLE(register_table, 8);
+ DECLARE_BITMAP(page_bitmap, MAX_EVENTS);
+ refcount_t refcnt;
+ int id;
+};

-static DEFINE_MUTEX(reg_mutex);
-static DEFINE_HASHTABLE(register_table, 8);
-static DECLARE_BITMAP(page_bitmap, MAX_EVENTS);
+static DEFINE_HASHTABLE(group_table, 8);
+static DEFINE_MUTEX(group_mutex);
+static struct user_event_group *root_group;

/*
* Stores per-event properties, as users register events
@@ -83,6 +95,7 @@ static DECLARE_BITMAP(page_bitmap, MAX_EVENTS);
* refcnt reaches one.
*/
struct user_event {
+ struct user_event_group *group;
struct tracepoint tracepoint;
struct trace_event_call call;
struct trace_event_class class;
@@ -109,6 +122,11 @@ struct user_event_refs {
struct user_event *events[];
};

+struct user_event_file_info {
+ struct user_event_group *group;
+ struct user_event_refs *refs;
+};
+
#define VALIDATOR_ENSURE_NULL (1 << 0)
#define VALIDATOR_REL (1 << 1)

@@ -121,7 +139,8 @@ struct user_event_validator {
typedef void (*user_event_func_t) (struct user_event *user, struct iov_iter *i,
void *tpdata, bool *faulted);

-static int user_event_parse(char *name, char *args, char *flags,
+static int user_event_parse(struct user_event_group *group, char *name,
+ char *args, char *flags,
struct user_event **newuser);

static u32 user_event_key(char *name)
@@ -129,12 +148,132 @@ static u32 user_event_key(char *name)
return jhash(name, strlen(name), 0);
}

+static void set_page_reservations(char *pages, bool set)
+{
+ int page;
+
+ for (page = 0; page < MAX_PAGES; ++page) {
+ void *addr = pages + (PAGE_SIZE * page);
+
+ if (set)
+ SetPageReserved(virt_to_page(addr));
+ else
+ ClearPageReserved(virt_to_page(addr));
+ }
+}
+
+static void user_event_group_destroy(struct user_event_group *group)
+{
+ if (group->status_file)
+ tracefs_remove(group->status_file);
+
+ if (group->data_file)
+ tracefs_remove(group->data_file);
+
+ if (group->register_page_data)
+ set_page_reservations(group->register_page_data, false);
+
+ if (group->pages)
+ __free_pages(group->pages, MAX_PAGE_ORDER);
+
+ kfree(group->system_name);
+ kfree(group);
+}
+
+static char *user_event_group_system_name(const char *name)
+{
+ char *system_name;
+ int len = strlen(name) + sizeof(USER_EVENTS_SYSTEM) + 1;
+
+ system_name = kmalloc(len, GFP_KERNEL);
+
+ if (!system_name)
+ return NULL;
+
+ snprintf(system_name, len, "%s.%s", USER_EVENTS_SYSTEM, name);
+
+ return system_name;
+}
+
+static __always_inline
+void user_event_group_release(struct user_event_group *group)
+{
+ refcount_dec(&group->refcnt);
+}
+
+static struct user_event_group *user_event_group_find(int id)
+{
+ struct user_event_group *group;
+
+ mutex_lock(&group_mutex);
+
+ hash_for_each_possible(group_table, group, node, id)
+ if (group->id == id) {
+ refcount_inc(&group->refcnt);
+ mutex_unlock(&group_mutex);
+ return group;
+ }
+
+ mutex_unlock(&group_mutex);
+
+ return NULL;
+}
+
+static struct user_event_group *user_event_group_create(const char *name,
+ int id)
+{
+ struct user_event_group *group;
+
+ group = kzalloc(sizeof(*group), GFP_KERNEL);
+
+ if (!group)
+ return NULL;
+
+ if (name) {
+ group->system_name = user_event_group_system_name(name);
+
+ if (!group->system_name)
+ goto error;
+ }
+
+ group->pages = alloc_pages(GFP_KERNEL | __GFP_ZERO, MAX_PAGE_ORDER);
+
+ if (!group->pages)
+ goto error;
+
+ group->register_page_data = page_address(group->pages);
+
+ set_page_reservations(group->register_page_data, true);
+
+ /* Zero all bits beside 0 (which is reserved for failures) */
+ bitmap_zero(group->page_bitmap, MAX_EVENTS);
+ set_bit(0, group->page_bitmap);
+
+ mutex_init(&group->reg_mutex);
+ hash_init(group->register_table);
+
+ /* Mark and add to lookup */
+ group->id = id;
+ refcount_set(&group->refcnt, 2);
+
+ mutex_lock(&group_mutex);
+ hash_add(group_table, &group->node, group->id);
+ mutex_unlock(&group_mutex);
+
+ return group;
+error:
+ if (group)
+ user_event_group_destroy(group);
+
+ return NULL;
+};
+
static __always_inline
void user_event_register_set(struct user_event *user)
{
int i = user->index;

- register_page_data[MAP_STATUS_BYTE(i)] |= MAP_STATUS_MASK(i);
+ user->group->register_page_data[MAP_STATUS_BYTE(i)] |= MAP_STATUS_MASK(i);
}

static __always_inline
@@ -142,7 +281,7 @@ void user_event_register_clear(struct user_event *user)
{
int i = user->index;

- register_page_data[MAP_STATUS_BYTE(i)] &= ~MAP_STATUS_MASK(i);
+ user->group->register_page_data[MAP_STATUS_BYTE(i)] &= ~MAP_STATUS_MASK(i);
}

static __always_inline __must_check
@@ -186,7 +325,8 @@ static struct list_head *user_event_get_fields(struct trace_event_call *call)
*
* Upon success user_event has its ref count increased by 1.
*/
-static int user_event_parse_cmd(char *raw_command, struct user_event **newuser)
+static int user_event_parse_cmd(struct user_event_group *group,
+ char *raw_command, struct user_event **newuser)
{
char *name = raw_command;
char *args = strpbrk(name, " ");
@@ -200,7 +340,7 @@ static int user_event_parse_cmd(char *raw_command, struct user_event **newuser)
if (flags)
*flags++ = '\0';

- return user_event_parse(name, args, flags, newuser);
+ return user_event_parse(group, name, args, flags, newuser);
}

static int user_field_array_size(const char *type)
@@ -688,7 +828,7 @@ static int destroy_user_event(struct user_event *user)
dyn_event_remove(&user->devent);

user_event_register_clear(user);
- clear_bit(user->index, page_bitmap);
+ clear_bit(user->index, user->group->page_bitmap);
hash_del(&user->node);

user_event_destroy_validators(user);
@@ -699,14 +839,15 @@ static int destroy_user_event(struct user_event *user)
return ret;
}

-static struct user_event *find_user_event(char *name, u32 *outkey)
+static struct user_event *find_user_event(struct user_event_group *group,
+ char *name, u32 *outkey)
{
struct user_event *user;
u32 key = user_event_key(name);

*outkey = key;

- hash_for_each_possible(register_table, user, node, key)
+ hash_for_each_possible(group->register_table, user, node, key)
if (!strcmp(EVENT_NAME(user), name)) {
refcount_inc(&user->refcnt);
return user;
@@ -953,14 +1094,14 @@ static int user_event_create(const char *raw_command)
if (!name)
return -ENOMEM;

- mutex_lock(&reg_mutex);
+ mutex_lock(&root_group->reg_mutex);

- ret = user_event_parse_cmd(name, &user);
+ ret = user_event_parse_cmd(root_group, name, &user);

if (!ret)
refcount_dec(&user->refcnt);

- mutex_unlock(&reg_mutex);
+ mutex_unlock(&root_group->reg_mutex);

if (ret)
kfree(name);
@@ -1114,7 +1255,8 @@ static int user_event_trace_register(struct user_event *user)
* The name buffer lifetime is owned by this method for success cases only.
* Upon success the returned user_event has its ref count increased by 1.
*/
-static int user_event_parse(char *name, char *args, char *flags,
+static int user_event_parse(struct user_event_group *group, char *name,
+ char *args, char *flags,
struct user_event **newuser)
{
int ret;
@@ -1124,7 +1266,7 @@ static int user_event_parse(char *name, char *args, char *flags,

/* Prevent dyn_event from racing */
mutex_lock(&event_mutex);
- user = find_user_event(name, &key);
+ user = find_user_event(group, name, &key);
mutex_unlock(&event_mutex);

if (user) {
@@ -1137,7 +1279,7 @@ static int user_event_parse(char *name, char *args, char *flags,
return 0;
}

- index = find_first_zero_bit(page_bitmap, MAX_EVENTS);
+ index = find_first_zero_bit(group->page_bitmap, MAX_EVENTS);

if (index == MAX_EVENTS)
return -EMFILE;
@@ -1151,6 +1293,7 @@ static int user_event_parse(char *name, char *args, char *flags,
INIT_LIST_HEAD(&user->fields);
INIT_LIST_HEAD(&user->validators);

+ user->group = group;
user->tracepoint.name = name;

ret = user_event_parse_fields(user, args);
@@ -1170,7 +1313,11 @@ static int user_event_parse(char *name, char *args, char *flags,
user->call.tp = &user->tracepoint;
user->call.event.funcs = &user_event_funcs;

- user->class.system = USER_EVENTS_SYSTEM;
+ if (group->system_name)
+ user->class.system = group->system_name;
+ else
+ user->class.system = USER_EVENTS_SYSTEM;
+
user->class.fields_array = user_event_fields_array;
user->class.get_fields = user_event_get_fields;
user->class.reg = user_event_reg;
@@ -1193,8 +1340,8 @@ static int user_event_parse(char *name, char *args, char *flags,

dyn_event_init(&user->devent, &user_event_dops);
dyn_event_add(&user->devent, &user->call);
- set_bit(user->index, page_bitmap);
- hash_add(register_table, &user->node, key);
+ set_bit(user->index, group->page_bitmap);
+ hash_add(group->register_table, &user->node, key);

mutex_unlock(&event_mutex);

@@ -1212,10 +1359,10 @@ static int user_event_parse(char *name, char *args, char *flags,
/*
* Deletes a previously created event if it is no longer being used.
*/
-static int delete_user_event(char *name)
+static int delete_user_event(struct user_event_group *group, char *name)
{
u32 key;
- struct user_event *user = find_user_event(name, &key);
+ struct user_event *user = find_user_event(group, name, &key);

if (!user)
return -ENOENT;
@@ -1233,6 +1380,7 @@ static int delete_user_event(char *name)
*/
static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
{
+ struct user_event_file_info *info = file->private_data;
struct user_event_refs *refs;
struct user_event *user = NULL;
struct tracepoint *tp;
@@ -1244,7 +1392,7 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)

rcu_read_lock_sched();

- refs = rcu_dereference_sched(file->private_data);
+ refs = rcu_dereference_sched(info->refs);

/*
* The refs->events array is protected by RCU, and new items may be
@@ -1302,6 +1450,30 @@ static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
return ret;
}

+static int user_events_open(struct inode *node, struct file *file)
+{
+ struct user_event_group *group;
+ struct user_event_file_info *info;
+
+ group = user_event_group_find((int)(uintptr_t)node->i_private);
+
+ if (!group)
+ return -ENOENT;
+
+ info = kzalloc(sizeof(*info), GFP_KERNEL);
+
+ if (!info) {
+ user_event_group_release(group);
+ return -ENOMEM;
+ }
+
+ info->group = group;
+
+ file->private_data = info;
+
+ return 0;
+}
+
static ssize_t user_events_write(struct file *file, const char __user *ubuf,
size_t count, loff_t *ppos)
{
@@ -1323,13 +1495,15 @@ static ssize_t user_events_write_iter(struct kiocb *kp, struct iov_iter *i)
return user_events_write_core(kp->ki_filp, i);
}

-static int user_events_ref_add(struct file *file, struct user_event *user)
+static int user_events_ref_add(struct user_event_file_info *info,
+ struct user_event *user)
{
+ struct user_event_group *group = info->group;
struct user_event_refs *refs, *new_refs;
int i, size, count = 0;

- refs = rcu_dereference_protected(file->private_data,
- lockdep_is_held(&reg_mutex));
+ refs = rcu_dereference_protected(info->refs,
+ lockdep_is_held(&group->reg_mutex));

if (refs) {
count = refs->count;
@@ -1355,7 +1529,7 @@ static int user_events_ref_add(struct file *file, struct user_event *user)

refcount_inc(&user->refcnt);

- rcu_assign_pointer(file->private_data, new_refs);
+ rcu_assign_pointer(info->refs, new_refs);

if (refs)
kfree_rcu(refs, rcu);
@@ -1392,7 +1566,8 @@ static long user_reg_get(struct user_reg __user *ureg, struct user_reg *kreg)
/*
* Registers a user_event on behalf of a user process.
*/
-static long user_events_ioctl_reg(struct file *file, unsigned long uarg)
+static long user_events_ioctl_reg(struct user_event_file_info *info,
+ unsigned long uarg)
{
struct user_reg __user *ureg = (struct user_reg __user *)uarg;
struct user_reg reg;
@@ -1413,14 +1588,14 @@ static long user_events_ioctl_reg(struct file *file, unsigned long uarg)
return ret;
}

- ret = user_event_parse_cmd(name, &user);
+ ret = user_event_parse_cmd(info->group, name, &user);

if (ret) {
kfree(name);
return ret;
}

- ret = user_events_ref_add(file, user);
+ ret = user_events_ref_add(info, user);

/* No longer need parse ref, ref_add either worked or not */
refcount_dec(&user->refcnt);
@@ -1438,7 +1613,8 @@ static long user_events_ioctl_reg(struct file *file, unsigned long uarg)
/*
* Deletes a user_event on behalf of a user process.
*/
-static long user_events_ioctl_del(struct file *file, unsigned long uarg)
+static long user_events_ioctl_del(struct user_event_file_info *info,
+ unsigned long uarg)
{
void __user *ubuf = (void __user *)uarg;
char *name;
@@ -1451,7 +1627,7 @@ static long user_events_ioctl_del(struct file *file, unsigned long uarg)

/* event_mutex prevents dyn_event from racing */
mutex_lock(&event_mutex);
- ret = delete_user_event(name);
+ ret = delete_user_event(info->group, name);
mutex_unlock(&event_mutex);

kfree(name);
@@ -1465,19 +1641,21 @@ static long user_events_ioctl_del(struct file *file, unsigned long uarg)
static long user_events_ioctl(struct file *file, unsigned int cmd,
unsigned long uarg)
{
+ struct user_event_file_info *info = file->private_data;
+ struct user_event_group *group = info->group;
long ret = -ENOTTY;

switch (cmd) {
case DIAG_IOCSREG:
- mutex_lock(&reg_mutex);
- ret = user_events_ioctl_reg(file, uarg);
- mutex_unlock(&reg_mutex);
+ mutex_lock(&group->reg_mutex);
+ ret = user_events_ioctl_reg(info, uarg);
+ mutex_unlock(&group->reg_mutex);
break;

case DIAG_IOCSDEL:
- mutex_lock(&reg_mutex);
- ret = user_events_ioctl_del(file, uarg);
- mutex_unlock(&reg_mutex);
+ mutex_lock(&group->reg_mutex);
+ ret = user_events_ioctl_del(info, uarg);
+ mutex_unlock(&group->reg_mutex);
break;
}

@@ -1489,17 +1667,24 @@ static long user_events_ioctl(struct file *file, unsigned int cmd,
*/
static int user_events_release(struct inode *node, struct file *file)
{
+ struct user_event_file_info *info = file->private_data;
+ struct user_event_group *group;
struct user_event_refs *refs;
struct user_event *user;
int i;

+ if (!info)
+ return -EINVAL;
+
+ group = info->group;
+
/*
* Ensure refs cannot change under any situation by taking the
* register mutex during the final freeing of the references.
*/
- mutex_lock(&reg_mutex);
+ mutex_lock(&group->reg_mutex);

- refs = file->private_data;
+ refs = info->refs;

if (!refs)
goto out;
@@ -1518,32 +1703,54 @@ static int user_events_release(struct inode *node, struct file *file)
out:
file->private_data = NULL;

- mutex_unlock(&reg_mutex);
+ mutex_unlock(&group->reg_mutex);

kfree(refs);
+ kfree(info);
+
+ /* No longer using group */
+ user_event_group_release(group);

return 0;
}

static const struct file_operations user_data_fops = {
+ .open = user_events_open,
.write = user_events_write,
.write_iter = user_events_write_iter,
.unlocked_ioctl = user_events_ioctl,
.release = user_events_release,
};

+static struct user_event_group *user_status_group(struct file *file)
+{
+ struct seq_file *m = file->private_data;
+
+ if (!m)
+ return NULL;
+
+ return m->private;
+}
+
/*
* Maps the shared page into the user process for checking if event is enabled.
*/
static int user_status_mmap(struct file *file, struct vm_area_struct *vma)
{
+ char *pages;
+ struct user_event_group *group = user_status_group(file);
unsigned long size = vma->vm_end - vma->vm_start;

if (size != MAX_BYTES)
return -EINVAL;

+ if (!group)
+ return -EINVAL;
+
+ pages = group->register_page_data;
+
return remap_pfn_range(vma, vma->vm_start,
- virt_to_phys(register_page_data) >> PAGE_SHIFT,
+ virt_to_phys(pages) >> PAGE_SHIFT,
size, vm_get_page_prot(VM_READ));
}

@@ -1567,13 +1774,17 @@ static void user_seq_stop(struct seq_file *m, void *p)

static int user_seq_show(struct seq_file *m, void *p)
{
+ struct user_event_group *group = m->private;
struct user_event *user;
char status;
int i, active = 0, busy = 0, flags;

- mutex_lock(&reg_mutex);
+ if (!group)
+ return -EINVAL;
+
+ mutex_lock(&group->reg_mutex);

- hash_for_each(register_table, i, user, node) {
+ hash_for_each(group->register_table, i, user, node) {
status = user->status;
flags = user->flags;

@@ -1597,7 +1808,7 @@ static int user_seq_show(struct seq_file *m, void *p)
active++;
}

- mutex_unlock(&reg_mutex);
+ mutex_unlock(&group->reg_mutex);

seq_puts(m, "\n");
seq_printf(m, "Active: %d\n", active);
@@ -1616,7 +1827,38 @@ static const struct seq_operations user_seq_ops = {

static int user_status_open(struct inode *node, struct file *file)
{
- return seq_open(file, &user_seq_ops);
+ struct user_event_group *group;
+ int ret;
+
+ group = user_event_group_find((int)(uintptr_t)node->i_private);
+
+ if (!group)
+ return -ENOENT;
+
+ ret = seq_open(file, &user_seq_ops);
+
+ if (!ret) {
+ /* Chain group to seq_file */
+ struct seq_file *m = file->private_data;
+
+ m->private = group;
+ } else {
+ user_event_group_release(group);
+ }
+
+ return ret;
+}
+
+static int user_status_release(struct inode *node, struct file *file)
+{
+ struct user_event_group *group = user_status_group(file);
+
+ if (group)
+ user_event_group_release(group);
+ else
+ pr_warn("user_events: No group attached to status file\n");
+
+ return seq_release(node, file);
}

static const struct file_operations user_status_fops = {
@@ -1624,18 +1866,20 @@ static const struct file_operations user_status_fops = {
.mmap = user_status_mmap,
.read = seq_read,
.llseek = seq_lseek,
- .release = seq_release,
+ .release = user_status_release,
};

/*
* Creates a set of tracefs files to allow user mode interactions.
*/
-static int create_user_tracefs(void)
+static int create_user_tracefs(struct dentry *parent,
+ struct user_event_group *group)
{
struct dentry *edata, *emmap;

edata = tracefs_create_file("user_events_data", TRACE_MODE_WRITE,
- NULL, NULL, &user_data_fops);
+ parent, (void *)(uintptr_t)group->id,
+ &user_data_fops);

if (!edata) {
pr_warn("Could not create tracefs 'user_events_data' entry\n");
@@ -1644,7 +1888,8 @@ static int create_user_tracefs(void)

/* mmap with MAP_SHARED requires writable fd */
emmap = tracefs_create_file("user_events_status", TRACE_MODE_WRITE,
- NULL, NULL, &user_status_fops);
+ parent, (void *)(uintptr_t)group->id,
+ &user_status_fops);

if (!emmap) {
tracefs_remove(edata);
@@ -1652,47 +1897,29 @@ static int create_user_tracefs(void)
goto err;
}

+ group->data_file = edata;
+ group->status_file = emmap;
+
return 0;
err:
return -ENODEV;
}

-static void set_page_reservations(bool set)
-{
- int page;
-
- for (page = 0; page < MAX_PAGES; ++page) {
- void *addr = register_page_data + (PAGE_SIZE * page);
-
- if (set)
- SetPageReserved(virt_to_page(addr));
- else
- ClearPageReserved(virt_to_page(addr));
- }
-}
-
static int __init trace_events_user_init(void)
{
- struct page *pages;
int ret;

- /* Zero all bits beside 0 (which is reserved for failures) */
- bitmap_zero(page_bitmap, MAX_EVENTS);
- set_bit(0, page_bitmap);
+ root_group = user_event_group_create(NULL, 0);

- pages = alloc_pages(GFP_KERNEL | __GFP_ZERO, MAX_PAGE_ORDER);
- if (!pages)
+ if (!root_group)
return -ENOMEM;
- register_page_data = page_address(pages);
-
- set_page_reservations(true);

- ret = create_user_tracefs();
+ ret = create_user_tracefs(NULL, root_group);

if (ret) {
pr_warn("user_events could not register with tracefs\n");
- set_page_reservations(false);
- __free_pages(pages, MAX_PAGE_ORDER);
+ user_event_group_destroy(root_group);
+ root_group = NULL;
return ret;
}

--
2.25.1