Make sure the event_mutex is properly held during dyn_event_add call.
This is required when adding dynamic events.
Link: https://lkml.kernel.org/r/20220328223225.1992-1-beaub@linux.microsoft.com
Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Tracefs by default is locked down heavily. System operators can open up
some files, such as user_events to a broader set of users. These users
do not have access within tracefs beyond just the user_event files. Due
to this restriction the trace_add_event_call/remove calls will silently
fail since the caller does not have permissions to create directories.
To fix this trace_add_event_call/remove calls will be issued with
override creds of the global root UID. Creds are reverted immediately
afterward.
Link: https://lkml.kernel.org/r/20220308222807.2040-1-beaub@linux.microsoft.com
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Find user_events always while under the event_mutex and before leaving
the lock, add a ref count to the user_event. This ensures that all paths
under the event_mutex that check the ref counts will be synchronized.
The ioctl add/delete paths are protected by the reg_mutex. However,
dyn_event is only protected by the event_mutex. The dyn_event delete
path cannot acquire reg_mutex, since that could cause a deadlock between
the ioctl delete case acquiring event_mutex after acquiring the reg_mutex.
Link: https://lkml.kernel.org/r/20220310001141.1660-1-beaub@linux.microsoft.com
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Add validation to ensure data is at or greater than the min size for the
fields of the event. If a dynamic array is used and is a type of char,
ensure null termination of the array exists.
Link: https://lkml.kernel.org/r/20220118204326.2169-7-beaub@linux.microsoft.com
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Pass iterator through to probes to allow copying data directly to the
probe buffers instead of taking multiple copies. Enables eBPF user and
raw iterator types out to programs for no-copy scenarios.
Link: https://lkml.kernel.org/r/20220118204326.2169-6-beaub@linux.microsoft.com
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Adds support to write out user_event data to perf_probe/perf files as
well as to any attached eBPF program.
Link: https://lkml.kernel.org/r/20220118204326.2169-5-beaub@linux.microsoft.com
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Ensures that when dynamic events requests a match with arguments that
they match what is in the user_event.
Link: https://lkml.kernel.org/r/20220118204326.2169-4-beaub@linux.microsoft.com
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Addes print_fmt format generation for basic types that are supported for
user processes. Only supports sizes that are the same on 32 and 64 bit.
Link: https://lkml.kernel.org/r/20220118204326.2169-3-beaub@linux.microsoft.com
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Minimal support for interacting with dynamic events, trace_event and
ftrace. Core outline of flow between user process, ioctl and trace_event
APIs.
User mode processes that wish to use trace events to get data into
ftrace, perf, eBPF, etc are limited to uprobes today. The user events
features enables an ABI for user mode processes to create and write to
trace events that are isolated from kernel level trace events. This
enables a faster path for tracing from user mode data as well as opens
managed code to participate in trace events, where stub locations are
dynamic.
User processes often want to trace only when it's useful. To enable this
a set of pages are mapped into the user process space that indicate the
current state of the user events that have been registered. User
processes can check if their event is hooked to a trace/probe, and if it
is, emit the event data out via the write() syscall.
Two new files are introduced into tracefs to accomplish this:
user_events_status - This file is mmap'd into participating user mode
processes to indicate event status.
user_events_data - This file is opened and register/delete ioctl's are
issued to create/open/delete trace events that can be used for tracing.
The typical scenario is on process start to mmap user_events_status. Processes
then register the events they plan to use via the REG ioctl. The ioctl reads
and updates the passed in user_reg struct. The status_index of the struct is
used to know the byte in the status page to check for that event. The
write_index of the struct is used to describe that event when writing out to
the fd that was used for the ioctl call. The data must always include this
index first when writing out data for an event. Data can be written either by
write() or by writev().
For example, in memory:
int index;
char data[];
Psuedo code example of typical usage:
struct user_reg reg;
int page_fd = open("user_events_status", O_RDWR);
char *page_data = mmap(NULL, PAGE_SIZE, PROT_READ, MAP_SHARED, page_fd, 0);
close(page_fd);
int data_fd = open("user_events_data", O_RDWR);
reg.size = sizeof(reg);
reg.name_args = (__u64)"test";
ioctl(data_fd, DIAG_IOCSREG, ®);
int status_id = reg.status_index;
int write_id = reg.write_index;
struct iovec io[2];
io[0].iov_base = &write_id;
io[0].iov_len = sizeof(write_id);
io[1].iov_base = payload;
io[1].iov_len = sizeof(payload);
if (page_data[status_id])
writev(data_fd, io, 2);
User events are also exposed via the dynamic_events tracefs file for
both create and delete. Current status is exposed via the user_events_status
tracefs file.
Simple example to register a user event via dynamic_events:
echo u:test >> dynamic_events
cat dynamic_events
u:test
If an event is hooked to a probe, the probe hooked shows up:
echo 1 > events/user_events/test/enable
cat user_events_status
1:test # Used by ftrace
Active: 1
Busy: 1
Max: 4096
If an event is not hooked to a probe, no probe status shows up:
echo 0 > events/user_events/test/enable
cat user_events_status
1:test
Active: 1
Busy: 0
Max: 4096
Users can describe the trace event format via the following format:
name[:FLAG1[,FLAG2...] [field1[;field2...]]
Each field has the following format:
type name
Example for char array with a size of 20 named msg:
echo 'u:detailed char[20] msg' >> dynamic_events
cat dynamic_events
u:detailed char[20] msg
Data offsets are based on the data written out via write() and will be
updated to reflect the correct offset in the trace_event fields. For dynamic
data it is recommended to use the new __rel_loc data type. This type will be
the same as __data_loc, but the offset is relative to this entry. This allows
user_events to not worry about what common fields are being inserted before
the data.
The above format is valid for both the ioctl and the dynamic_events file.
Link: https://lkml.kernel.org/r/20220118204326.2169-2-beaub@linux.microsoft.com
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
