| Message ID | 20211201182515.2446-3-beaub@linux.microsoft.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | user_events: Enable user processes to create and write to trace events | expand |
On Wed, 1 Dec 2021 10:25:04 -0800 Beau Belgrave <beaub@linux.microsoft.com> wrote: > Minimal support for interacting with dynamic events, trace_event and > ftrace. Core outline of flow between user process, ioctl and trace_event > APIs. > > Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com> > --- > kernel/trace/Kconfig | 15 + > kernel/trace/Makefile | 1 + > kernel/trace/trace_events_user.c | 1192 ++++++++++++++++++++++++++++++ > 3 files changed, 1208 insertions(+) > create mode 100644 kernel/trace/trace_events_user.c > > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig > index 420ff4bc67fd..21d00092436b 100644 > --- a/kernel/trace/Kconfig > +++ b/kernel/trace/Kconfig > @@ -724,6 +724,21 @@ config SYNTH_EVENTS > > If in doubt, say N. > > +config USER_EVENTS > + bool "User trace events" > + select TRACING > + select DYNAMIC_EVENTS > + default n default n is default, so you do not need to explicitly state that. In other words, the above line is a nop. > + help > + User trace events are user-defined trace events that > + can be used like an existing kernel trace event. User trace > + events are generated by writing to a tracefs file. User > + processes can determine if their tracing events should be > + generated by memory mapping a tracefs file and checking for > + an associated byte being non-zero. > + > + If in doubt, say N. > + > config HIST_TRIGGERS > bool "Histogram triggers" > depends on ARCH_HAVE_NMI_SAFE_CMPXCHG > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile > index bedc5caceec7..19ef3758da95 100644 > --- a/kernel/trace/Makefile > +++ b/kernel/trace/Makefile > +/* > + * Handles the final close of the file from user mode. > + */ > +static int user_events_release(struct inode *node, struct file *file) > +{ > + struct user_event_refs *refs; > + struct user_event *user; > + int i; > + > + /* > + * refs is protected by RCU and could in theory change immediately > + * before this call on another core. To ensure we read the latest > + * version of refs we acquire the RCU read lock again. > + */ > + rcu_read_lock_sched(); > + refs = rcu_dereference_sched(file->private_data); > + rcu_read_unlock_sched(); This still bothers me. Can another CPU call an ioctl here? user_events_ioctl_reg() { user_events_ref_add() { refs = rcu_dereference_protected(file->private_data, ..); new_refs = kzalloc(size, GFP_KERNEL); rcu_assign_pointer(file->private_data, new_refs); if (refs) kfree_rcu(refs, rcu); refs now freed. > + > + if (!refs) > + goto out; > + > + /* > + * Do not need RCU while enumerating the events that were used. > + * The lifetime of refs has reached an end, it's tied to this file. > + * The underlying user_events are ref counted, and cannot be freed. > + * After this decrement, the user_events may be freed elsewhere. > + */ > + for (i = 0; i < refs->count; ++i) { Fault on refs->count ?? > + user = refs->events[i]; > + > + if (user) > + atomic_dec(&user->refcnt); > + } > + > + kfree_rcu(refs, rcu); > +out: > + return 0; > +} > + > +static const struct file_operations user_data_fops = { > + .write = user_events_write, > + .write_iter = user_events_write_iter, > + .unlocked_ioctl = user_events_ioctl, > + .release = user_events_release, > +}; > + > +/* > + * 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) > +{ > + unsigned long size = vma->vm_end - vma->vm_start; > + > + if (size != MAX_EVENTS) > + return -EINVAL; > + > + return remap_pfn_range(vma, vma->vm_start, > + virt_to_phys(register_page_data) >> PAGE_SHIFT, > + size, vm_get_page_prot(VM_READ)); > +} > + > +static int user_status_show(struct seq_file *m, void *p) > +{ > + struct user_event *user; > + char status; > + int i, active = 0, busy = 0, flags; > + > + mutex_lock(®_mutex); > + > + hash_for_each(register_table, i, user, node) { > + status = register_page_data[user->index]; > + flags = user->flags; > + > + seq_printf(m, "%d:%s", user->index, EVENT_NAME(user)); > + > + if (flags != 0 || status != 0) > + seq_puts(m, " #"); > + > + if (status != 0) { > + seq_puts(m, " Used by"); > + if (status & EVENT_STATUS_FTRACE) > + seq_puts(m, " ftrace"); > + if (status & EVENT_STATUS_PERF) > + seq_puts(m, " perf"); > + if (status & EVENT_STATUS_OTHER) > + seq_puts(m, " other"); > + busy++; > + } > + > + if (flags & FLAG_BPF_ITER) > + seq_puts(m, " FLAG:BPF_ITER"); > + > + seq_puts(m, "\n"); > + active++; > + } > + > + mutex_unlock(®_mutex); > + > + seq_puts(m, "\n"); > + seq_printf(m, "Active: %d\n", active); > + seq_printf(m, "Busy: %d\n", busy); > + seq_printf(m, "Max: %ld\n", MAX_EVENTS); > + > + return 0; > +} > + > +static ssize_t user_status_read(struct file *file, char __user *ubuf, > + size_t count, loff_t *ppos) > +{ > + /* > + * Delay allocation of seq data until requested, most callers > + * will never read the status file. They will only mmap. > + */ > + if (file->private_data == NULL) { > + int ret; > + > + if (*ppos != 0) > + return -EINVAL; > + > + ret = single_open(file, user_status_show, NULL); > + > + if (ret) > + return ret; > + } > + > + return seq_read(file, ubuf, count, ppos); > +} > + > +static loff_t user_status_seek(struct file *file, loff_t offset, int whence) > +{ > + if (file->private_data == NULL) > + return 0; > + > + return seq_lseek(file, offset, whence); > +} > + > +static int user_status_release(struct inode *node, struct file *file) > +{ > + if (file->private_data == NULL) > + return 0; > + > + return single_release(node, file); > +} > + > +static const struct file_operations user_status_fops = { > + .mmap = user_status_mmap, > + .read = user_status_read, > + .llseek = user_status_seek, > + .release = user_status_release, > +}; > + > +/* > + * Creates a set of tracefs files to allow user mode interactions. > + */ > +static int create_user_tracefs(void) > +{ > + struct dentry *edata, *emmap; > + > + edata = tracefs_create_file("user_events_data", 0644, NULL, > + NULL, &user_data_fops); BTW, I now define: TRACE_MODE_WRITE for files to be written to, and TRACE_MODE_READ for files that are read only. And soon tracefs will honor the gid mount option to define what group all the tracefs files should belong to on mount. -- Steve > + > + if (!edata) { > + pr_warn("Could not create tracefs 'user_events_data' entry\n"); > + goto err; > + } > + > + /* mmap with MAP_SHARED requires writable fd */ > + emmap = tracefs_create_file("user_events_status", 0644, NULL, > + NULL, &user_status_fops); > + > + if (!emmap) { > + tracefs_remove(edata); > + pr_warn("Could not create tracefs 'user_events_mmap' entry\n"); > + goto err; > + } > + > + 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) > +{ > + int ret; > + > + /* Zero all bits beside 0 (which is reserved for failures) */ > + bitmap_zero(page_bitmap, MAX_EVENTS); > + set_bit(0, page_bitmap); > + > + register_page_data = kzalloc(MAX_EVENTS, GFP_KERNEL); > + > + if (!register_page_data) > + return -ENOMEM; > + > + set_page_reservations(true); > + > + ret = create_user_tracefs(); > + > + if (ret) { > + pr_warn("user_events could not register with tracefs\n"); > + set_page_reservations(false); > + kfree(register_page_data); > + return ret; > + } > + > + if (dyn_event_register(&user_event_dops)) > + pr_warn("user_events could not register with dyn_events\n"); > + > + return 0; > +} > + > +fs_initcall(trace_events_user_init);
On Wed, Dec 08, 2021 at 06:19:05PM -0500, Steven Rostedt wrote: > On Wed, 1 Dec 2021 10:25:04 -0800 > Beau Belgrave <beaub@linux.microsoft.com> wrote: > > > Minimal support for interacting with dynamic events, trace_event and > > ftrace. Core outline of flow between user process, ioctl and trace_event > > APIs. > > > > Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com> > > --- > > kernel/trace/Kconfig | 15 + > > kernel/trace/Makefile | 1 + > > kernel/trace/trace_events_user.c | 1192 ++++++++++++++++++++++++++++++ > > 3 files changed, 1208 insertions(+) > > create mode 100644 kernel/trace/trace_events_user.c > > > > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig > > index 420ff4bc67fd..21d00092436b 100644 > > --- a/kernel/trace/Kconfig > > +++ b/kernel/trace/Kconfig > > @@ -724,6 +724,21 @@ config SYNTH_EVENTS > > > > If in doubt, say N. > > > > +config USER_EVENTS > > + bool "User trace events" > > + select TRACING > > + select DYNAMIC_EVENTS > > + default n > > default n is default, so you do not need to explicitly state that. > > In other words, the above line is a nop. > Got it. > > + help > > + User trace events are user-defined trace events that > > + can be used like an existing kernel trace event. User trace > > + events are generated by writing to a tracefs file. User > > + processes can determine if their tracing events should be > > + generated by memory mapping a tracefs file and checking for > > + an associated byte being non-zero. > > + > > + If in doubt, say N. > > + > > config HIST_TRIGGERS > > bool "Histogram triggers" > > depends on ARCH_HAVE_NMI_SAFE_CMPXCHG > > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile > > index bedc5caceec7..19ef3758da95 100644 > > --- a/kernel/trace/Makefile > > +++ b/kernel/trace/Makefile > > > > > > +/* > > + * Handles the final close of the file from user mode. > > + */ > > +static int user_events_release(struct inode *node, struct file *file) > > +{ > > + struct user_event_refs *refs; > > + struct user_event *user; > > + int i; > > + > > + /* > > + * refs is protected by RCU and could in theory change immediately > > + * before this call on another core. To ensure we read the latest > > + * version of refs we acquire the RCU read lock again. > > + */ > > + rcu_read_lock_sched(); > > + refs = rcu_dereference_sched(file->private_data); > > + rcu_read_unlock_sched(); > > This still bothers me. Can another CPU call an ioctl here? Sorry :) No, another CPU cannot call the ioctl on the file, since if another CPU had a reference to this file release couldn't be called. user_events_release is only called when the final reference to the file has been closed, so there cannot be another ioctl pending, starting or finishing for this file at the time it is called. The last user mode program to call close() on the file will end up invoking user_events_release. The user_event_refs is only accessible via the file's private_data, which now has zero references when release is executing. This means the private_data can no longer change and the rcu deref ensures we have the latest version. refs is per-file, so while there can be other ioctl's occurring for other files, they are completely different ref objects than the one being cleaned up in the release of the file, it's not shared outside of this file lifetime, which has now ended. > > user_events_ioctl_reg() { > user_events_ref_add() { > refs = rcu_dereference_protected(file->private_data, ..); > new_refs = kzalloc(size, GFP_KERNEL); > rcu_assign_pointer(file->private_data, new_refs); > if (refs) > kfree_rcu(refs, rcu); > > refs now freed. > If user_events_ioctl is executing for that same file, user_events_release could not have been called due to the file being in use to issue the ioctl. > > + > > + if (!refs) > > + goto out; > > + > > + /* > > + * Do not need RCU while enumerating the events that were used. > > + * The lifetime of refs has reached an end, it's tied to this file. > > + * The underlying user_events are ref counted, and cannot be freed. > > + * After this decrement, the user_events may be freed elsewhere. > > + */ > > + for (i = 0; i < refs->count; ++i) { > > Fault on refs->count > > ?? refs after rcu_dereference is checked for null before accessing. refs cannot be changed when release is being executed, since that would mean the ioctl ran without a file reference (not sure how that could happen). This is why it's important that release get the latest version of refs, an ioctl could have JUST happened before the final close() in user mode, and if it jumped CPUs we could (in theory) get an old value. If we got an old value, then yes, the fault could occur. This code uses the file ops release method as a final sync point to clean up everything for that file only after there are no more references to it at all, so nobody can do this kind of thing. Is there some case I am missing where an ioctl on a file can be performed without a reference to that file? Are you worried about a malicious user calling close on the file and then immediately issuing an ioctl on the now closed file? If so, wouldn't ioctl just reject that file reference being used as not in the processes file table / invalid and not let the ioctl go through? > > > + user = refs->events[i]; > > + > > + if (user) > > + atomic_dec(&user->refcnt); > > + } > > + > > + kfree_rcu(refs, rcu); > > +out: > > + return 0; > > +} > > + [..] > > +static const struct file_operations user_status_fops = { > > + .mmap = user_status_mmap, > > + .read = user_status_read, > > + .llseek = user_status_seek, > > + .release = user_status_release, > > +}; > > + > > +/* > > + * Creates a set of tracefs files to allow user mode interactions. > > + */ > > +static int create_user_tracefs(void) > > +{ > > + struct dentry *edata, *emmap; > > + > > + edata = tracefs_create_file("user_events_data", 0644, NULL, > > + NULL, &user_data_fops); > > BTW, I now define: > > TRACE_MODE_WRITE for files to be written to, and TRACE_MODE_READ for files > that are read only. > > And soon tracefs will honor the gid mount option to define what group all > the tracefs files should belong to on mount. Perfect, thank you. > > -- Steve > Thanks, -Beau
On Wed, 8 Dec 2021 16:58:23 -0800 Beau Belgrave <beaub@linux.microsoft.com> wrote: > > > > > +/* > > > + * Handles the final close of the file from user mode. > > > + */ > > > +static int user_events_release(struct inode *node, struct file > > > *file) +{ > > > + struct user_event_refs *refs; > > > + struct user_event *user; > > > + int i; > > > + > > > + /* > > > + * refs is protected by RCU and could in theory change > > > immediately > > > + * before this call on another core. To ensure we read > > > the latest > > > + * version of refs we acquire the RCU read lock again. > > > + */ > > > + rcu_read_lock_sched(); > > > + refs = rcu_dereference_sched(file->private_data); > > > + rcu_read_unlock_sched(); > > > > This still bothers me. Can another CPU call an ioctl here? > > Sorry :) > > No, another CPU cannot call the ioctl on the file, since if another > CPU had a reference to this file release couldn't be called. OK, so it should be good, as the last fdput() will call this (and the ioctl should keep that from happening until its done). But this could also be done with less confusion and less paranoia if we simply take the reg_mutex, as that should keep everything from changing, and we wouldn't need to do any rcu_read_lock*() from the release function. > > user_events_release is only called when the final reference to the > file has been closed, so there cannot be another ioctl pending, > starting or finishing for this file at the time it is called. > > The last user mode program to call close() on the file will end up > invoking user_events_release. It doesn't work like that. There's only one close(). But you are correct that it is protected, and that's by the fdget() and fdput() that is done within the ioctl (and other) system call. > > The user_event_refs is only accessible via the file's private_data, > which now has zero references when release is executing. This means > the private_data can no longer change and the rcu deref ensures we > have the latest version. > > refs is per-file, so while there can be other ioctl's occurring for > other files, they are completely different ref objects than the one > being cleaned up in the release of the file, it's not shared outside > of this file lifetime, which has now ended. Right, but I'm still paranoid ;-) > > > > > user_events_ioctl_reg() { > > user_events_ref_add() { > > refs = rcu_dereference_protected(file->private_data, ..); > > new_refs = kzalloc(size, GFP_KERNEL); > > rcu_assign_pointer(file->private_data, new_refs); > > if (refs) > > kfree_rcu(refs, rcu); > > > > refs now freed. > > > > If user_events_ioctl is executing for that same file, > user_events_release could not have been called due to the file being > in use to issue the ioctl. The only thing protecting against this is the fdget/put logic in the system calls. > > > > + > > > + if (!refs) > > > + goto out; > > > + > > > + /* > > > + * Do not need RCU while enumerating the events that > > > were used. > > > + * The lifetime of refs has reached an end, it's tied to > > > this file. > > > + * The underlying user_events are ref counted, and > > > cannot be freed. > > > + * After this decrement, the user_events may be freed > > > elsewhere. > > > + */ > > > + for (i = 0; i < refs->count; ++i) { > > > > Fault on refs->count > > > > ?? > > refs after rcu_dereference is checked for null before accessing. > > refs cannot be changed when release is being executed, since that > would mean the ioctl ran without a file reference (not sure how that > could happen). > > This is why it's important that release get the latest version of > refs, an ioctl could have JUST happened before the final close() in > user mode, and if it jumped CPUs we could (in theory) get an old > value. If we got an old value, then yes, the fault could occur. > > This code uses the file ops release method as a final sync point to > clean up everything for that file only after there are no more > references to it at all, so nobody can do this kind of thing. > > Is there some case I am missing where an ioctl on a file can be > performed without a reference to that file? Well, the ioctl can be called as the close happens, but it's the internal working of fdget/put that protects it. If the ioctl is called at the same time as the close, the fdget in the ioctl will keep the close from calling the release. And as soon as the ioctl is finished, it will call the fdput() which then calls the release logic. > > Are you worried about a malicious user calling close on the file and > then immediately issuing an ioctl on the now closed file? > > If so, wouldn't ioctl just reject that file reference being used as > not in the processes file table / invalid and not let the ioctl go > through? > I think it seems less confusing and saner to just use the mutex. It's not a fast path is it? -- Steve
On Wed, Dec 08, 2021 at 09:03:36PM -0500, Steven Rostedt wrote: > On Wed, 8 Dec 2021 16:58:23 -0800 > Beau Belgrave <beaub@linux.microsoft.com> wrote: > > > > > > > +/* > > > > + * Handles the final close of the file from user mode. > > > > + */ > > > > +static int user_events_release(struct inode *node, struct file > > > > *file) +{ > > > > + struct user_event_refs *refs; > > > > + struct user_event *user; > > > > + int i; > > > > + > > > > + /* > > > > + * refs is protected by RCU and could in theory change > > > > immediately > > > > + * before this call on another core. To ensure we read > > > > the latest > > > > + * version of refs we acquire the RCU read lock again. > > > > + */ > > > > + rcu_read_lock_sched(); > > > > + refs = rcu_dereference_sched(file->private_data); > > > > + rcu_read_unlock_sched(); > > > > > > This still bothers me. Can another CPU call an ioctl here? > > > > Sorry :) > > > > No, another CPU cannot call the ioctl on the file, since if another > > CPU had a reference to this file release couldn't be called. > > OK, so it should be good, as the last fdput() will call this (and the > ioctl should keep that from happening until its done). But this could > also be done with less confusion and less paranoia if we simply take > the reg_mutex, as that should keep everything from changing, and we > wouldn't need to do any rcu_read_lock*() from the release function. > Sure, could do that. This shouldn't be a fast path scenario, however I dislike taking global locks when not required. Happy to change this though. I'm guessing for less confusion and paranoia you'd want the lock held for the entire method call? > > > > user_events_release is only called when the final reference to the > > file has been closed, so there cannot be another ioctl pending, > > starting or finishing for this file at the time it is called. > > > > The last user mode program to call close() on the file will end up > > invoking user_events_release. > > It doesn't work like that. There's only one close(). But you are > correct that it is protected, and that's by the fdget() and fdput() > that is done within the ioctl (and other) system call. > Yeah, I simplified to user space. IE: fork() then close() in each process / task. We both understand each other now though ;) > > > > The user_event_refs is only accessible via the file's private_data, > > which now has zero references when release is executing. This means > > the private_data can no longer change and the rcu deref ensures we > > have the latest version. > > > > refs is per-file, so while there can be other ioctl's occurring for > > other files, they are completely different ref objects than the one > > being cleaned up in the release of the file, it's not shared outside > > of this file lifetime, which has now ended. > > Right, but I'm still paranoid ;-) > > > > > > > > > user_events_ioctl_reg() { > > > user_events_ref_add() { > > > refs = rcu_dereference_protected(file->private_data, ..); > > > new_refs = kzalloc(size, GFP_KERNEL); > > > rcu_assign_pointer(file->private_data, new_refs); > > > if (refs) > > > kfree_rcu(refs, rcu); > > > > > > refs now freed. > > > > > > > If user_events_ioctl is executing for that same file, > > user_events_release could not have been called due to the file being > > in use to issue the ioctl. > > > The only thing protecting against this is the fdget/put logic in the > system calls. > Yes, however, it is protected. > > > > > > + > > > > + if (!refs) > > > > + goto out; > > > > + > > > > + /* > > > > + * Do not need RCU while enumerating the events that > > > > were used. > > > > + * The lifetime of refs has reached an end, it's tied to > > > > this file. > > > > + * The underlying user_events are ref counted, and > > > > cannot be freed. > > > > + * After this decrement, the user_events may be freed > > > > elsewhere. > > > > + */ > > > > + for (i = 0; i < refs->count; ++i) { > > > > > > Fault on refs->count > > > > > > ?? > > > > refs after rcu_dereference is checked for null before accessing. > > > > refs cannot be changed when release is being executed, since that > > would mean the ioctl ran without a file reference (not sure how that > > could happen). > > > > This is why it's important that release get the latest version of > > refs, an ioctl could have JUST happened before the final close() in > > user mode, and if it jumped CPUs we could (in theory) get an old > > value. If we got an old value, then yes, the fault could occur. > > > > This code uses the file ops release method as a final sync point to > > clean up everything for that file only after there are no more > > references to it at all, so nobody can do this kind of thing. > > > > Is there some case I am missing where an ioctl on a file can be > > performed without a reference to that file? > > > Well, the ioctl can be called as the close happens, but it's the > internal working of fdget/put that protects it. If the ioctl is called > at the same time as the close, the fdget in the ioctl will keep the > close from calling the release. And as soon as the ioctl is finished, > it will call the fdput() which then calls the release logic. > > > > > Are you worried about a malicious user calling close on the file and > > then immediately issuing an ioctl on the now closed file? > > > > If so, wouldn't ioctl just reject that file reference being used as > > not in the processes file table / invalid and not let the ioctl go > > through? > > > > I think it seems less confusing and saner to just use the mutex. It's > not a fast path is it? > > -- Steve No, this is not a fast path, and I don't have a problem moving to a mutex if you feel that is better. I've likely become too close to this code to know when things are confusing for others. Thanks, -Beau
On Thu, 9 Dec 2021 09:40:50 -0800 Beau Belgrave <beaub@linux.microsoft.com> wrote: > No, this is not a fast path, and I don't have a problem moving to a > mutex if you feel that is better. I've likely become too close to this > code to know when things are confusing for others. Yeah. I really dislike the "protection by algorithms" then protection by locking unless it is a fast path. If this was a fast path then I'd be more concerned. I dislike global locks as well, but unless contention becomes a concern, I don't think we should worry about it. Also, for this comment: +static int user_events_release(struct inode *node, struct file *file) +{ + struct user_event_refs *refs; + struct user_event *user; + int i; + + /* + * refs is protected by RCU and could in theory change immediately + * before this call on another core. To ensure we read the latest + * version of refs we acquire the RCU read lock again. + */ + rcu_read_lock_sched(); + refs = rcu_dereference_sched(file->private_data); + rcu_read_unlock_sched(); How do you see refs changing on another core if this can only be called when nothing has a reference to it? I think this comment and grabbing the rcu locks is what is causing me concern. -- Steve
On Thu, Dec 09, 2021 at 12:47:35PM -0500, Steven Rostedt wrote: > On Thu, 9 Dec 2021 09:40:50 -0800 > Beau Belgrave <beaub@linux.microsoft.com> wrote: > > > No, this is not a fast path, and I don't have a problem moving to a > > mutex if you feel that is better. I've likely become too close to this > > code to know when things are confusing for others. > > Yeah. I really dislike the "protection by algorithms" then protection by > locking unless it is a fast path. > > If this was a fast path then I'd be more concerned. I dislike global locks > as well, but unless contention becomes a concern, I don't think we should > worry about it. Sure thing. > > Also, for this comment: > > +static int user_events_release(struct inode *node, struct file *file) > +{ > + struct user_event_refs *refs; > + struct user_event *user; > + int i; > + > + /* > + * refs is protected by RCU and could in theory change immediately > + * before this call on another core. To ensure we read the latest > + * version of refs we acquire the RCU read lock again. > + */ > + rcu_read_lock_sched(); > + refs = rcu_dereference_sched(file->private_data); > + rcu_read_unlock_sched(); > > How do you see refs changing on another core if this can only be called > when nothing has a reference to it? > > I think this comment and grabbing the rcu locks is what is causing me > concern. > > -- Steve User program task: CPU0: ioctl(fd, REG) CPU1: close(fd) IE: Some program registers and then immediately calls close on the file. If the CPU migrates right between the 2 and the close swaps, it is possible this could occur. This could be attempted in tight loops maliciously as well. I assume with a mutex there that some barrier is imposed to ensure correct reads in this condition? (By virtue of the mutex acquire/check) Thanks, -Beau
On Thu, 9 Dec 2021 11:42:35 -0800 Beau Belgrave <beaub@linux.microsoft.com> wrote: > User program task: > CPU0: ioctl(fd, REG) > CPU1: close(fd) > > IE: Some program registers and then immediately calls close on the file. > If the CPU migrates right between the 2 and the close swaps, it is > possible this could occur. > > This could be attempted in tight loops maliciously as well. > > I assume with a mutex there that some barrier is imposed to ensure > correct reads in this condition? (By virtue of the mutex acquire/check) But as I stated before, the ioctl() uses fdget() which will prevent he close from calling the release. Even if they get swapped. If close goes first and starts down the path of the release, then the ioctl is guaranteed to return -EBADF. If it gets the fd, then close will be a nop, and the exit of the ioctl will call the release. If this wasn't the case, then the race I was concerned about would be an issue. Because we are both confused by this, add the mutex! :-) -- Steve
On Thu, Dec 09, 2021 at 02:57:38PM -0500, Steven Rostedt wrote: > On Thu, 9 Dec 2021 11:42:35 -0800 > Beau Belgrave <beaub@linux.microsoft.com> wrote: > > > User program task: > > CPU0: ioctl(fd, REG) > > CPU1: close(fd) > > > > IE: Some program registers and then immediately calls close on the file. > > If the CPU migrates right between the 2 and the close swaps, it is > > possible this could occur. > > > > This could be attempted in tight loops maliciously as well. > > > > I assume with a mutex there that some barrier is imposed to ensure > > correct reads in this condition? (By virtue of the mutex acquire/check) > > But as I stated before, the ioctl() uses fdget() which will prevent he > close from calling the release. Even if they get swapped. If close goes > first and starts down the path of the release, then the ioctl is guaranteed > to return -EBADF. If it gets the fd, then close will be a nop, and the exit > of the ioctl will call the release. > > If this wasn't the case, then the race I was concerned about would be an > issue. > > Because we are both confused by this, add the mutex! :-) > > -- Steve Agreed, I will add the mutex. :) I guess I am being paranoid about an architecture that does not have automatic cache consistency and while the write / read don't happen at the exact time, they happen close together. Close enough that one CPU reads the old value from a cache line and gets it wrong. I don't believe that is possible on Intel, but I don't know if it's possible on other architectures (especially older ones). Thanks, -Beau
On Thu, 9 Dec 2021 12:11:12 -0800 Beau Belgrave <beaub@linux.microsoft.com> wrote: > I guess I am being paranoid about an architecture that does not have > automatic cache consistency and while the write / read don't happen at > the exact time, they happen close together. Close enough that one CPU > reads the old value from a cache line and gets it wrong. > > I don't believe that is possible on Intel, but I don't know if it's > possible on other architectures (especially older ones). If this was possible, then there would be a lot more bugs out there than this one. For one thing, the file descriptor itself would be freed while accessed. -- Steve
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 420ff4bc67fd..21d00092436b 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -724,6 +724,21 @@ config SYNTH_EVENTS If in doubt, say N. +config USER_EVENTS + bool "User trace events" + select TRACING + select DYNAMIC_EVENTS + default n + help + User trace events are user-defined trace events that + can be used like an existing kernel trace event. User trace + events are generated by writing to a tracefs file. User + processes can determine if their tracing events should be + generated by memory mapping a tracefs file and checking for + an associated byte being non-zero. + + If in doubt, say N. + config HIST_TRIGGERS bool "Histogram triggers" depends on ARCH_HAVE_NMI_SAFE_CMPXCHG diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index bedc5caceec7..19ef3758da95 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -82,6 +82,7 @@ obj-$(CONFIG_PROBE_EVENTS) += trace_eprobe.o obj-$(CONFIG_TRACE_EVENT_INJECT) += trace_events_inject.o obj-$(CONFIG_SYNTH_EVENTS) += trace_events_synth.o obj-$(CONFIG_HIST_TRIGGERS) += trace_events_hist.o +obj-$(CONFIG_USER_EVENTS) += trace_events_user.o obj-$(CONFIG_BPF_EVENTS) += bpf_trace.o obj-$(CONFIG_KPROBE_EVENTS) += trace_kprobe.o obj-$(CONFIG_TRACEPOINTS) += error_report-traces.o diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c new file mode 100644 index 000000000000..afcf224b941d --- /dev/null +++ b/kernel/trace/trace_events_user.c @@ -0,0 +1,1192 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (c) 2021, Microsoft Corporation. + * + * Authors: + * Beau Belgrave <beaub@linux.microsoft.com> + */ + +#include <linux/bitmap.h> +#include <linux/cdev.h> +#include <linux/hashtable.h> +#include <linux/list.h> +#include <linux/io.h> +#include <linux/uio.h> +#include <linux/ioctl.h> +#include <linux/jhash.h> +#include <linux/trace_events.h> +#include <linux/tracefs.h> +#include <linux/types.h> +#include <linux/uaccess.h> +#include <uapi/linux/user_events.h> +#include "trace.h" +#include "trace_dynevent.h" + +#define USER_EVENTS_PREFIX_LEN (sizeof(USER_EVENTS_PREFIX)-1) + +#define FIELD_DEPTH_TYPE 0 +#define FIELD_DEPTH_NAME 1 +#define FIELD_DEPTH_SIZE 2 + +/* + * Limits how many trace_event calls user processes can create: + * Must be multiple of PAGE_SIZE. + */ +#define MAX_PAGES 1 +#define MAX_EVENTS (MAX_PAGES * PAGE_SIZE) + +/* Limit how long of an event name plus args within the subsystem. */ +#define MAX_EVENT_DESC 512 +#define EVENT_NAME(user_event) ((user_event)->tracepoint.name) +#define MAX_FIELD_ARRAY_SIZE (2 * PAGE_SIZE) + +static char *register_page_data; + +static DEFINE_MUTEX(reg_mutex); +static DEFINE_HASHTABLE(register_table, 4); +static DECLARE_BITMAP(page_bitmap, MAX_EVENTS); + +/* + * Stores per-event properties, as users register events + * within a file a user_event might be created if it does not + * already exist. These are globally used and their lifetime + * is tied to the refcnt member. These cannot go away until the + * refcnt reaches zero. + */ +struct user_event { + struct tracepoint tracepoint; + struct trace_event_call call; + struct trace_event_class class; + struct dyn_event devent; + struct hlist_node node; + struct list_head fields; + atomic_t refcnt; + int index; + int flags; +}; + +/* + * Stores per-file events references, as users register events + * within a file this structure is modified and freed via RCU. + * The lifetime of this struct is tied to the lifetime of the file. + * These are not shared and only accessible by the file that created it. + */ +struct user_event_refs { + struct rcu_head rcu; + int count; + struct user_event *events[]; +}; + +typedef void (*user_event_func_t) (struct user_event *user, + void *data, u32 datalen, + void *tpdata); + +static int user_event_parse(char *name, char *args, char *flags, + struct user_event **newuser); + +static u32 user_event_key(char *name) +{ + return jhash(name, strlen(name), 0); +} + +static struct list_head *user_event_get_fields(struct trace_event_call *call) +{ + struct user_event *user = (struct user_event *)call->data; + + return &user->fields; +} + +/* + * Parses a register command for user_events + * Format: event_name[:FLAG1[,FLAG2...]] [field1[;field2...]] + * + * Example event named test with a 20 char msg field with a unsigned int after: + * test char[20] msg;unsigned int id + * + * NOTE: Offsets are from the user data perspective, they are not from the + * trace_entry/buffer perspective. We automatically add the common properties + * sizes to the offset for the user. + */ +static int user_event_parse_cmd(char *raw_command, struct user_event **newuser) +{ + char *name = raw_command; + char *args = strpbrk(name, " "); + char *flags; + + if (args) + *args++ = 0; + + flags = strpbrk(name, ":"); + + if (flags) + *flags++ = 0; + + return user_event_parse(name, args, flags, newuser); +} + +static int user_field_array_size(const char *type) +{ + const char *start = strchr(type, '['); + char val[8]; + int size = 0; + + if (start == NULL) + return -EINVAL; + + start++; + + while (*start != ']' && size < (sizeof(val) - 1)) + val[size++] = *start++; + + if (*start != ']') + return -EINVAL; + + val[size] = 0; + + if (kstrtouint(val, 0, &size)) + return -EINVAL; + + if (size > MAX_FIELD_ARRAY_SIZE) + return -EINVAL; + + return size; +} + +static int user_field_size(const char *type) +{ + /* long is not allowed from a user, since it's ambigious in size */ + if (strcmp(type, "s64") == 0) + return sizeof(s64); + if (strcmp(type, "u64") == 0) + return sizeof(u64); + if (strcmp(type, "s32") == 0) + return sizeof(s32); + if (strcmp(type, "u32") == 0) + return sizeof(u32); + if (strcmp(type, "int") == 0) + return sizeof(int); + if (strcmp(type, "unsigned int") == 0) + return sizeof(unsigned int); + if (strcmp(type, "s16") == 0) + return sizeof(s16); + if (strcmp(type, "u16") == 0) + return sizeof(u16); + if (strcmp(type, "short") == 0) + return sizeof(short); + if (strcmp(type, "unsigned short") == 0) + return sizeof(unsigned short); + if (strcmp(type, "s8") == 0) + return sizeof(s8); + if (strcmp(type, "u8") == 0) + return sizeof(u8); + if (strcmp(type, "char") == 0) + return sizeof(char); + if (strcmp(type, "unsigned char") == 0) + return sizeof(unsigned char); + if (str_has_prefix(type, "char[")) + return user_field_array_size(type); + if (str_has_prefix(type, "unsigned char[")) + return user_field_array_size(type); + if (str_has_prefix(type, "__data_loc ")) + return sizeof(u32); + if (str_has_prefix(type, "__rel_loc ")) + return sizeof(u32); + + /* Uknown basic type, error */ + return -EINVAL; +} + +static void user_event_destroy_fields(struct user_event *user) +{ + struct ftrace_event_field *field, *next; + struct list_head *head = &user->fields; + + list_for_each_entry_safe(field, next, head, link) { + list_del(&field->link); + kfree(field); + } +} + +static int user_event_add_field(struct user_event *user, const char *type, + const char *name, int offset, int size, + int is_signed, int filter_type) +{ + struct ftrace_event_field *field; + + field = kmalloc(sizeof(*field), GFP_KERNEL); + + if (!field) + return -ENOMEM; + + field->type = type; + field->name = name; + field->offset = offset; + field->size = size; + field->is_signed = is_signed; + field->filter_type = filter_type; + + list_add(&field->link, &user->fields); + + return 0; +} + +/* + * Parses the values of a field within the description + * Format: type name [size] + */ +static int user_event_parse_field(char *field, struct user_event *user, + u32 *offset) +{ + char *part, *type, *name; + u32 depth = 0, saved_offset = *offset; + int len, size = -EINVAL; + bool is_struct = false; + + field = skip_spaces(field); + + if (*field == 0) + return 0; + + /* Handle types that have a space within */ + len = str_has_prefix(field, "unsigned "); + if (len) + goto skip_next; + + len = str_has_prefix(field, "struct "); + if (len) { + is_struct = true; + goto skip_next; + } + + len = str_has_prefix(field, "__data_loc unsigned "); + if (len) + goto skip_next; + + len = str_has_prefix(field, "__data_loc "); + if (len) + goto skip_next; + + len = str_has_prefix(field, "__rel_loc unsigned "); + if (len) + goto skip_next; + + len = str_has_prefix(field, "__rel_loc "); + if (len) + goto skip_next; + + goto parse; +skip_next: + type = field; + field = strpbrk(field + len, " "); + + if (field == NULL) + return -EINVAL; + + *field++ = 0; + depth++; +parse: + while ((part = strsep(&field, " ")) != NULL) { + switch (depth++) { + case FIELD_DEPTH_TYPE: + type = part; + break; + case FIELD_DEPTH_NAME: + name = part; + break; + case FIELD_DEPTH_SIZE: + if (!is_struct) + return -EINVAL; + + if (kstrtou32(part, 10, &size)) + return -EINVAL; + break; + default: + return -EINVAL; + } + } + + if (depth < FIELD_DEPTH_SIZE) + return -EINVAL; + + if (depth == FIELD_DEPTH_SIZE) + size = user_field_size(type); + + if (size == 0) + return -EINVAL; + + if (size < 0) + return size; + + *offset = saved_offset + size; + + return user_event_add_field(user, type, name, saved_offset, size, + type[0] != 'u', FILTER_OTHER); +} + +static void user_event_parse_flags(struct user_event *user, char *flags) +{ + char *flag; + + if (flags == NULL) + return; + + while ((flag = strsep(&flags, ",")) != NULL) { + if (strcmp(flag, "BPF_ITER") == 0) + user->flags |= FLAG_BPF_ITER; + } +} + +static int user_event_parse_fields(struct user_event *user, char *args) +{ + char *field; + u32 offset = sizeof(struct trace_entry); + int ret = -EINVAL; + + if (args == NULL) + return 0; + + while ((field = strsep(&args, ";")) != NULL) { + ret = user_event_parse_field(field, user, &offset); + + if (ret) + break; + } + + return ret; +} + +static struct trace_event_fields user_event_fields_array[1]; + +static enum print_line_t user_event_print_trace(struct trace_iterator *iter, + int flags, + struct trace_event *event) +{ + /* Unsafe to try to decode user provided print_fmt, use hex */ + trace_print_hex_dump_seq(&iter->seq, "", DUMP_PREFIX_OFFSET, 16, + 1, iter->ent, iter->ent_size, true); + + return trace_handle_return(&iter->seq); +} + +static struct trace_event_functions user_event_funcs = { + .trace = user_event_print_trace, +}; + +static int destroy_user_event(struct user_event *user) +{ + int ret = 0; + + /* Must destroy fields before call removal */ + user_event_destroy_fields(user); + + ret = trace_remove_event_call(&user->call); + + if (ret) + return ret; + + dyn_event_remove(&user->devent); + + register_page_data[user->index] = 0; + clear_bit(user->index, page_bitmap); + hash_del(&user->node); + + kfree(EVENT_NAME(user)); + kfree(user); + + return ret; +} + +static struct user_event *find_user_event(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) + if (!strcmp(EVENT_NAME(user), name)) + return user; + + return NULL; +} + +/* + * Writes the user supplied payload out to a trace file. + */ +static void user_event_ftrace(struct user_event *user, void *data, u32 datalen, + void *tpdata) +{ + struct trace_event_file *file; + struct trace_entry *entry; + struct trace_event_buffer event_buffer; + + file = (struct trace_event_file *)tpdata; + + if (!file || + !(file->flags & EVENT_FILE_FL_ENABLED) || + trace_trigger_soft_disabled(file)) + return; + + /* Allocates and fills trace_entry, + 1 of this is data payload */ + entry = trace_event_buffer_reserve(&event_buffer, file, + sizeof(*entry) + datalen); + + if (unlikely(!entry)) + return; + + memcpy(entry + 1, data, datalen); + + trace_event_buffer_commit(&event_buffer); +} + +/* + * Update the register page that is shared between user processes. + */ +static void update_reg_page_for(struct user_event *user) +{ + struct tracepoint *tp = &user->tracepoint; + char status = 0; + + if (atomic_read(&tp->key.enabled) > 0) { + struct tracepoint_func *probe_func_ptr; + user_event_func_t probe_func; + + rcu_read_lock_sched(); + + probe_func_ptr = rcu_dereference_sched(tp->funcs); + + if (probe_func_ptr) { + do { + probe_func = probe_func_ptr->func; + + if (probe_func == user_event_ftrace) + status |= EVENT_STATUS_FTRACE; + else + status |= EVENT_STATUS_OTHER; + } while ((++probe_func_ptr)->func); + } + + rcu_read_unlock_sched(); + } + + register_page_data[user->index] = status; +} + +/* + * Register callback for our events from tracing sub-systems. + */ +static int user_event_reg(struct trace_event_call *call, + enum trace_reg type, + void *data) +{ + struct user_event *user = (struct user_event *)call->data; + int ret = 0; + + if (!user) + return -ENOENT; + + switch (type) { + case TRACE_REG_REGISTER: + ret = tracepoint_probe_register(call->tp, + call->class->probe, + data); + if (!ret) + goto inc; + break; + + case TRACE_REG_UNREGISTER: + tracepoint_probe_unregister(call->tp, + call->class->probe, + data); + goto dec; + +#ifdef CONFIG_PERF_EVENTS + case TRACE_REG_PERF_REGISTER: + case TRACE_REG_PERF_UNREGISTER: + case TRACE_REG_PERF_OPEN: + case TRACE_REG_PERF_CLOSE: + case TRACE_REG_PERF_ADD: + case TRACE_REG_PERF_DEL: + break; +#endif + } + + return ret; +inc: + atomic_inc(&user->refcnt); + update_reg_page_for(user); + return 0; +dec: + update_reg_page_for(user); + atomic_dec(&user->refcnt); + return 0; +} + +static int user_event_create(const char *raw_command) +{ + struct user_event *user; + char *name; + int ret; + + if (!str_has_prefix(raw_command, USER_EVENTS_PREFIX)) + return -ECANCELED; + + raw_command += USER_EVENTS_PREFIX_LEN; + raw_command = skip_spaces(raw_command); + + name = kstrdup(raw_command, GFP_KERNEL); + + if (!name) + return -ENOMEM; + + mutex_lock(®_mutex); + ret = user_event_parse_cmd(name, &user); + mutex_unlock(®_mutex); + + if (ret) + kfree(name); + + return ret; +} + +static int user_event_show(struct seq_file *m, struct dyn_event *ev) +{ + struct user_event *user = container_of(ev, struct user_event, devent); + struct ftrace_event_field *field, *next; + struct list_head *head; + int depth = 0; + + seq_printf(m, "%s%s", USER_EVENTS_PREFIX, EVENT_NAME(user)); + + head = trace_get_fields(&user->call); + + list_for_each_entry_safe_reverse(field, next, head, link) { + if (depth == 0) + seq_puts(m, " "); + else + seq_puts(m, "; "); + seq_printf(m, "%s %s", field->type, field->name); + depth++; + } + + seq_puts(m, "\n"); + + return 0; +} + +static bool user_event_is_busy(struct dyn_event *ev) +{ + struct user_event *user = container_of(ev, struct user_event, devent); + + return atomic_read(&user->refcnt) != 0; +} + +static int user_event_free(struct dyn_event *ev) +{ + struct user_event *user = container_of(ev, struct user_event, devent); + + if (atomic_read(&user->refcnt) != 0) + return -EBUSY; + + return destroy_user_event(user); +} + +static bool user_event_match(const char *system, const char *event, + int argc, const char **argv, struct dyn_event *ev) +{ + struct user_event *user = container_of(ev, struct user_event, devent); + + return strcmp(EVENT_NAME(user), event) == 0 && + (!system || strcmp(system, USER_EVENTS_SYSTEM) == 0); +} + +static struct dyn_event_operations user_event_dops = { + .create = user_event_create, + .show = user_event_show, + .is_busy = user_event_is_busy, + .free = user_event_free, + .match = user_event_match, +}; + +static int user_event_trace_register(struct user_event *user) +{ + int ret; + + ret = register_trace_event(&user->call.event); + + if (!ret) + return -ENODEV; + + ret = trace_add_event_call(&user->call); + + if (ret) + unregister_trace_event(&user->call.event); + + return ret; +} + +/* + * Parses the event name, arguments and flags then registers if successful. + * The name buffer lifetime is owned by this method for success cases only. + */ +static int user_event_parse(char *name, char *args, char *flags, + struct user_event **newuser) +{ + int ret; + int index; + u32 key; + struct user_event *user = find_user_event(name, &key); + + if (user) { + *newuser = user; + /* + * Name is allocated by caller, free it since it already exists. + * Caller only worries about failure cases for freeing. + */ + kfree(name); + return 0; + } + + index = find_first_zero_bit(page_bitmap, MAX_EVENTS); + + if (index == MAX_EVENTS) + return -EMFILE; + + user = kzalloc(sizeof(*user), GFP_KERNEL); + + if (!user) + return -ENOMEM; + + INIT_LIST_HEAD(&user->class.fields); + INIT_LIST_HEAD(&user->fields); + + user->tracepoint.name = name; + + user_event_parse_flags(user, flags); + + ret = user_event_parse_fields(user, args); + + if (ret) + goto put_user; + + /* Minimal print format */ + user->call.print_fmt = "\"\""; + + user->call.data = user; + user->call.class = &user->class; + user->call.name = name; + user->call.flags = TRACE_EVENT_FL_TRACEPOINT; + user->call.tp = &user->tracepoint; + user->call.event.funcs = &user_event_funcs; + + 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; + user->class.probe = user_event_ftrace; + + mutex_lock(&event_mutex); + ret = user_event_trace_register(user); + mutex_unlock(&event_mutex); + + if (ret) + goto put_user; + + user->index = index; + 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); + + *newuser = user; + return 0; +put_user: + user_event_destroy_fields(user); + kfree(user); + return ret; +} + +/* + * Deletes a previously created event if it is no longer being used. + */ +static int delete_user_event(char *name) +{ + u32 key; + int ret; + struct user_event *user = find_user_event(name, &key); + + if (!user) + return -ENOENT; + + if (atomic_read(&user->refcnt) != 0) + return -EBUSY; + + mutex_lock(&event_mutex); + ret = destroy_user_event(user); + mutex_unlock(&event_mutex); + + return ret; +} + +/* + * Validates the user payload and writes via iterator. + */ +static ssize_t user_events_write_core(struct file *file, struct iov_iter *i) +{ + struct user_event_refs *refs; + struct user_event *user = NULL; + struct tracepoint *tp; + ssize_t ret = i->count; + int idx; + + if (unlikely(copy_from_iter(&idx, sizeof(idx), i) != sizeof(idx))) + return -EFAULT; + + rcu_read_lock_sched(); + + refs = rcu_dereference_sched(file->private_data); + + /* + * The refs->events array is protected by RCU, and new items may be + * added. But the user retrieved from indexing into the events array + * shall be immutable while the file is opened. + */ + if (likely(refs && idx < refs->count)) + user = refs->events[idx]; + + rcu_read_unlock_sched(); + + if (unlikely(user == NULL)) + return -ENOENT; + + tp = &user->tracepoint; + + /* + * It's possible key.enabled disables after this check, however + * we don't mind if a few events are included in this condition. + */ + if (likely(atomic_read(&tp->key.enabled) > 0)) { + struct tracepoint_func *probe_func_ptr; + user_event_func_t probe_func; + void *tpdata; + void *kdata; + u32 datalen; + + kdata = kmalloc(i->count, GFP_KERNEL); + + if (unlikely(!kdata)) + return -ENOMEM; + + datalen = copy_from_iter(kdata, i->count, i); + + rcu_read_lock_sched(); + + probe_func_ptr = rcu_dereference_sched(tp->funcs); + + if (probe_func_ptr) { + do { + probe_func = probe_func_ptr->func; + tpdata = probe_func_ptr->data; + probe_func(user, kdata, datalen, tpdata); + } while ((++probe_func_ptr)->func); + } + + rcu_read_unlock_sched(); + + kfree(kdata); + } + + return ret; +} + +static ssize_t user_events_write(struct file *file, const char __user *ubuf, + size_t count, loff_t *ppos) +{ + struct iovec iov; + struct iov_iter i; + + if (unlikely(*ppos != 0)) + return -EFAULT; + + if (unlikely(import_single_range(READ, (char *)ubuf, count, &iov, &i))) + return -EFAULT; + + return user_events_write_core(file, &i); +} + +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) +{ + struct user_event_refs *refs, *new_refs; + int i, size, count = 0; + + refs = rcu_dereference_protected(file->private_data, + lockdep_is_held(®_mutex)); + + if (refs) { + count = refs->count; + + for (i = 0; i < count; ++i) + if (refs->events[i] == user) + return i; + } + + size = struct_size(refs, events, count + 1); + + new_refs = kzalloc(size, GFP_KERNEL); + + if (!new_refs) + return -ENOMEM; + + new_refs->count = count + 1; + + for (i = 0; i < count; ++i) + new_refs->events[i] = refs->events[i]; + + new_refs->events[i] = user; + + atomic_inc(&user->refcnt); + + rcu_assign_pointer(file->private_data, new_refs); + + if (refs) + kfree_rcu(refs, rcu); + + return i; +} + +static long user_reg_get(struct user_reg __user *ureg, struct user_reg *kreg) +{ + u32 size; + long ret; + + ret = get_user(size, &ureg->size); + + if (ret) + return ret; + + if (size > PAGE_SIZE) + return -E2BIG; + + return copy_struct_from_user(kreg, sizeof(*kreg), ureg, size); +} + +/* + * Registers a user_event on behalf of a user process. + */ +static long user_events_ioctl_reg(struct file *file, unsigned long uarg) +{ + struct user_reg __user *ureg = (struct user_reg __user *)uarg; + struct user_reg reg; + struct user_event *user; + char *name; + long ret; + + ret = user_reg_get(ureg, ®); + + if (ret) + return ret; + + name = strndup_user((const char __user *)(uintptr_t)reg.name_args, + MAX_EVENT_DESC); + + if (IS_ERR(name)) { + ret = PTR_ERR(name); + return ret; + } + + ret = user_event_parse_cmd(name, &user); + + if (ret) { + kfree(name); + return ret; + } + + ret = user_events_ref_add(file, user); + + /* Positive number is index and valid */ + if (ret < 0) + return ret; + + put_user((u32)ret, &ureg->write_index); + put_user(user->index, &ureg->status_index); + + return 0; +} + +/* + * Deletes a user_event on behalf of a user process. + */ +static long user_events_ioctl_del(struct file *file, unsigned long uarg) +{ + void __user *ubuf = (void __user *)uarg; + char *name; + long ret; + + name = strndup_user(ubuf, MAX_EVENT_DESC); + + if (IS_ERR(name)) + return PTR_ERR(name); + + ret = delete_user_event(name); + + kfree(name); + + return ret; +} + +/* + * Handles the ioctl from user mode to register or alter operations. + */ +static long user_events_ioctl(struct file *file, unsigned int cmd, + unsigned long uarg) +{ + long ret = -ENOTTY; + + switch (cmd) { + case DIAG_IOCSREG: + mutex_lock(®_mutex); + ret = user_events_ioctl_reg(file, uarg); + mutex_unlock(®_mutex); + break; + + case DIAG_IOCSDEL: + mutex_lock(®_mutex); + ret = user_events_ioctl_del(file, uarg); + mutex_unlock(®_mutex); + break; + } + + return ret; +} + +/* + * Handles the final close of the file from user mode. + */ +static int user_events_release(struct inode *node, struct file *file) +{ + struct user_event_refs *refs; + struct user_event *user; + int i; + + /* + * refs is protected by RCU and could in theory change immediately + * before this call on another core. To ensure we read the latest + * version of refs we acquire the RCU read lock again. + */ + rcu_read_lock_sched(); + refs = rcu_dereference_sched(file->private_data); + rcu_read_unlock_sched(); + + if (!refs) + goto out; + + /* + * Do not need RCU while enumerating the events that were used. + * The lifetime of refs has reached an end, it's tied to this file. + * The underlying user_events are ref counted, and cannot be freed. + * After this decrement, the user_events may be freed elsewhere. + */ + for (i = 0; i < refs->count; ++i) { + user = refs->events[i]; + + if (user) + atomic_dec(&user->refcnt); + } + + kfree_rcu(refs, rcu); +out: + return 0; +} + +static const struct file_operations user_data_fops = { + .write = user_events_write, + .write_iter = user_events_write_iter, + .unlocked_ioctl = user_events_ioctl, + .release = user_events_release, +}; + +/* + * 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) +{ + unsigned long size = vma->vm_end - vma->vm_start; + + if (size != MAX_EVENTS) + return -EINVAL; + + return remap_pfn_range(vma, vma->vm_start, + virt_to_phys(register_page_data) >> PAGE_SHIFT, + size, vm_get_page_prot(VM_READ)); +} + +static int user_status_show(struct seq_file *m, void *p) +{ + struct user_event *user; + char status; + int i, active = 0, busy = 0, flags; + + mutex_lock(®_mutex); + + hash_for_each(register_table, i, user, node) { + status = register_page_data[user->index]; + flags = user->flags; + + seq_printf(m, "%d:%s", user->index, EVENT_NAME(user)); + + if (flags != 0 || status != 0) + seq_puts(m, " #"); + + if (status != 0) { + seq_puts(m, " Used by"); + if (status & EVENT_STATUS_FTRACE) + seq_puts(m, " ftrace"); + if (status & EVENT_STATUS_PERF) + seq_puts(m, " perf"); + if (status & EVENT_STATUS_OTHER) + seq_puts(m, " other"); + busy++; + } + + if (flags & FLAG_BPF_ITER) + seq_puts(m, " FLAG:BPF_ITER"); + + seq_puts(m, "\n"); + active++; + } + + mutex_unlock(®_mutex); + + seq_puts(m, "\n"); + seq_printf(m, "Active: %d\n", active); + seq_printf(m, "Busy: %d\n", busy); + seq_printf(m, "Max: %ld\n", MAX_EVENTS); + + return 0; +} + +static ssize_t user_status_read(struct file *file, char __user *ubuf, + size_t count, loff_t *ppos) +{ + /* + * Delay allocation of seq data until requested, most callers + * will never read the status file. They will only mmap. + */ + if (file->private_data == NULL) { + int ret; + + if (*ppos != 0) + return -EINVAL; + + ret = single_open(file, user_status_show, NULL); + + if (ret) + return ret; + } + + return seq_read(file, ubuf, count, ppos); +} + +static loff_t user_status_seek(struct file *file, loff_t offset, int whence) +{ + if (file->private_data == NULL) + return 0; + + return seq_lseek(file, offset, whence); +} + +static int user_status_release(struct inode *node, struct file *file) +{ + if (file->private_data == NULL) + return 0; + + return single_release(node, file); +} + +static const struct file_operations user_status_fops = { + .mmap = user_status_mmap, + .read = user_status_read, + .llseek = user_status_seek, + .release = user_status_release, +}; + +/* + * Creates a set of tracefs files to allow user mode interactions. + */ +static int create_user_tracefs(void) +{ + struct dentry *edata, *emmap; + + edata = tracefs_create_file("user_events_data", 0644, NULL, + NULL, &user_data_fops); + + if (!edata) { + pr_warn("Could not create tracefs 'user_events_data' entry\n"); + goto err; + } + + /* mmap with MAP_SHARED requires writable fd */ + emmap = tracefs_create_file("user_events_status", 0644, NULL, + NULL, &user_status_fops); + + if (!emmap) { + tracefs_remove(edata); + pr_warn("Could not create tracefs 'user_events_mmap' entry\n"); + goto err; + } + + 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) +{ + int ret; + + /* Zero all bits beside 0 (which is reserved for failures) */ + bitmap_zero(page_bitmap, MAX_EVENTS); + set_bit(0, page_bitmap); + + register_page_data = kzalloc(MAX_EVENTS, GFP_KERNEL); + + if (!register_page_data) + return -ENOMEM; + + set_page_reservations(true); + + ret = create_user_tracefs(); + + if (ret) { + pr_warn("user_events could not register with tracefs\n"); + set_page_reservations(false); + kfree(register_page_data); + return ret; + } + + if (dyn_event_register(&user_event_dops)) + pr_warn("user_events could not register with dyn_events\n"); + + return 0; +} + +fs_initcall(trace_events_user_init);
Minimal support for interacting with dynamic events, trace_event and ftrace. Core outline of flow between user process, ioctl and trace_event APIs. Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com> --- kernel/trace/Kconfig | 15 + kernel/trace/Makefile | 1 + kernel/trace/trace_events_user.c | 1192 ++++++++++++++++++++++++++++++ 3 files changed, 1208 insertions(+) create mode 100644 kernel/trace/trace_events_user.c