[for-linus][PATCH 4/7] tracing/user_events: Remove eBPF interfaces

Steven Rostedt
2022-04-03T14:31:56Z

From: Beau Belgrave <beaub@linux.microsoft.com>

Remove eBPF interfaces within user_events to ensure they are fully
reviewed.

Link: https://lore.kernel.org/all/20220329165718.GA10381@kbox/
Link: https://lkml.kernel.org/r/20220329173051.10087-1-beaub@linux.microsoft.com

Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Documentation/trace/user_events.rst | 14 ++----
include/uapi/linux/user_events.h | 53 ---------------------
kernel/trace/trace_events_user.c | 73 +----------------------------
3 files changed, 4 insertions(+), 136 deletions(-)

diff --git a/Documentation/trace/user_events.rst b/Documentation/trace/user_events.rst
index bddedabaca80..c180936f49fc 100644
--- a/Documentation/trace/user_events.rst
+++ b/Documentation/trace/user_events.rst
@@ -7,7 +7,7 @@ user_events: User-based Event Tracing
Overview
--------
User based trace events allow user processes to create events and trace data
-that can be viewed via existing tools, such as ftrace, perf and eBPF.
+that can be viewed via existing tools, such as ftrace and perf.
To enable this feature, build your kernel with CONFIG_USER_EVENTS=y.

Programs can view status of the events via
@@ -67,8 +67,7 @@ The command string format is as follows::

Supported Flags
^^^^^^^^^^^^^^^
-**BPF_ITER** - EBPF programs attached to this event will get the raw iovec
-struct instead of any data copies for max performance.
+None yet

Field Format
^^^^^^^^^^^^
@@ -160,7 +159,7 @@ The following values are defined to aid in checking what has been attached:

**EVENT_STATUS_FTRACE** - Bit set if ftrace has been attached (Bit 0).

-**EVENT_STATUS_PERF** - Bit set if perf/eBPF has been attached (Bit 1).
+**EVENT_STATUS_PERF** - Bit set if perf has been attached (Bit 1).

Writing Data
------------
@@ -204,13 +203,6 @@ It's advised for user programs to do the following::

**NOTE:** *The write_index is not emitted out into the trace being recorded.*

-EBPF
-----
-EBPF programs that attach to a user-based event tracepoint are given a pointer
-to a struct user_bpf_context. The bpf context contains the data type (which can
-be a user or kernel buffer, or can be a pointer to the iovec) and the data
-length that was emitted (minus the write_index).
-
Example Code
------------
See sample code in samples/user_events.
diff --git a/include/uapi/linux/user_events.h b/include/uapi/linux/user_events.h
index e570840571e1..736e05603463 100644
--- a/include/uapi/linux/user_events.h
+++ b/include/uapi/linux/user_events.h
@@ -32,9 +32,6 @@
/* Create dynamic location entry within a 32-bit value */
#define DYN_LOC(offset, size) ((size) << 16 | (offset))

-/* Use raw iterator for attached BPF program(s), no affect on ftrace/perf */
-#define FLAG_BPF_ITER (1 << 0)
-
/*
* Describes an event registration and stores the results of the registration.
* This structure is passed to the DIAG_IOCSREG ioctl, callers at a minimum
@@ -63,54 +60,4 @@ struct user_reg {
/* Requests to delete a user_event */
#define DIAG_IOCSDEL _IOW(DIAG_IOC_MAGIC, 1, char*)

-/* Data type that was passed to the BPF program */
-enum {
- /* Data resides in kernel space */
- USER_BPF_DATA_KERNEL,
-
- /* Data resides in user space */
- USER_BPF_DATA_USER,
-
- /* Data is a pointer to a user_bpf_iter structure */
- USER_BPF_DATA_ITER,
-};
-
-/*
- * Describes an iovec iterator that BPF programs can use to access data for
- * a given user_event write() / writev() call.
- */
-struct user_bpf_iter {
-
- /* Offset of the data within the first iovec */
- __u32 iov_offset;
-
- /* Number of iovec structures */
- __u32 nr_segs;
-
- /* Pointer to iovec structures */
- const struct iovec *iov;
-};
-
-/* Context that BPF programs receive when attached to a user_event */
-struct user_bpf_context {
-
- /* Data type being passed (see union below) */
- __u32 data_type;
-
- /* Length of the data */
- __u32 data_len;
-
- /* Pointer to data, varies by data type */
- union {
- /* Kernel data (data_type == USER_BPF_DATA_KERNEL) */
- void *kdata;
-
- /* User data (data_type == USER_BPF_DATA_USER) */
- void *udata;
-
- /* Direct iovec (data_type == USER_BPF_DATA_ITER) */
- struct user_bpf_iter *iter;
- };
-};
-
#endif /* _UAPI_LINUX_USER_EVENTS_H */
diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 61d78d64bdf0..846c27bc7aef 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -42,9 +42,6 @@
#define MAX_FIELD_ARRAY_SIZE 1024
#define MAX_FIELD_ARG_NAME 256

-#define MAX_BPF_COPY_SIZE PAGE_SIZE
-#define MAX_STACK_BPF_DATA 512
-
static char *register_page_data;

static DEFINE_MUTEX(reg_mutex);
@@ -405,19 +402,6 @@ static int user_event_parse_field(char *field, struct user_event *user,
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;
@@ -713,64 +697,14 @@ static void user_event_ftrace(struct user_event *user, struct iov_iter *i,
}

#ifdef CONFIG_PERF_EVENTS
-static void user_event_bpf(struct user_event *user, struct iov_iter *i)
-{
- struct user_bpf_context context;
- struct user_bpf_iter bpf_i;
- char fast_data[MAX_STACK_BPF_DATA];
- void *temp = NULL;
-
- if ((user->flags & FLAG_BPF_ITER) && iter_is_iovec(i)) {
- /* Raw iterator */
- context.data_type = USER_BPF_DATA_ITER;
- context.data_len = i->count;
- context.iter = &bpf_i;
-
- bpf_i.iov_offset = i->iov_offset;
- bpf_i.iov = i->iov;
- bpf_i.nr_segs = i->nr_segs;
- } else if (i->nr_segs == 1 && iter_is_iovec(i)) {
- /* Single buffer from user */
- context.data_type = USER_BPF_DATA_USER;
- context.data_len = i->count;
- context.udata = i->iov->iov_base + i->iov_offset;
- } else {
- /* Multi buffer from user */
- struct iov_iter copy = *i;
- size_t copy_size = min_t(size_t, i->count, MAX_BPF_COPY_SIZE);
-
- context.data_type = USER_BPF_DATA_KERNEL;
- context.kdata = fast_data;
-
- if (unlikely(copy_size > sizeof(fast_data))) {
- temp = kmalloc(copy_size, GFP_NOWAIT);
-
- if (temp)
- context.kdata = temp;
- else
- copy_size = sizeof(fast_data);
- }
-
- context.data_len = copy_nofault(context.kdata,
- copy_size, &copy);
- }
-
- trace_call_bpf(&user->call, &context);
-
- kfree(temp);
-}
-
/*
- * Writes the user supplied payload out to perf ring buffer or eBPF program.
+ * Writes the user supplied payload out to perf ring buffer.
*/
static void user_event_perf(struct user_event *user, struct iov_iter *i,
void *tpdata, bool *faulted)
{
struct hlist_head *perf_head;

- if (bpf_prog_array_valid(&user->call))
- user_event_bpf(user, i);
-
perf_head = this_cpu_ptr(user->call.perf_events);

if (perf_head && !hlist_empty(perf_head)) {
@@ -1136,8 +1070,6 @@ static int user_event_parse(char *name, char *args, char *flags,

user->tracepoint.name = name;

- user_event_parse_flags(user, flags);
-
ret = user_event_parse_fields(user, args);

if (ret)
@@ -1579,9 +1511,6 @@ static int user_seq_show(struct seq_file *m, void *p)
busy++;
}

- if (flags & FLAG_BPF_ITER)
- seq_puts(m, " FLAG:BPF_ITER");
-
seq_puts(m, "\n");
active++;
}
--
2.35.1