[PATCH bpf-next v3 13/21] bpf: add bpf_seq_printf and bpf_seq_write helpers

Yonghong Song
2020-05-07T05:39:48Z

Two helpers bpf_seq_printf and bpf_seq_write, are added for
writing data to the seq_file buffer.

bpf_seq_printf supports common format string flag/width/type
fields so at least I can get identical results for
netlink and ipv6_route targets.

For bpf_seq_printf and bpf_seq_write, return value -EOVERFLOW
specifically indicates a write failure due to overflow, which
means the object will be repeated in the next bpf invocation
if object collection stays the same. Note that if the object
collection is changed, depending how collection traversal is
done, even if the object still in the collection, it may not
be visited.

bpf_seq_printf may return -EBUSY meaning that internal percpu
buffer for memory copy of strings or other pointees is
not available. Bpf program can return 1 to indicate it
wants the same object to be repeated. Right now, this should not
happen on no-RT kernels since migrate_disable(), which guards
bpf prog call, calls preempt_disable().

Signed-off-by: Yonghong Song <yhs@fb.com>
---
include/uapi/linux/bpf.h | 32 +++++-
kernel/trace/bpf_trace.c | 200 +++++++++++++++++++++++++++++++++
scripts/bpf_helpers_doc.py | 2 +
tools/include/uapi/linux/bpf.h | 32 +++++-
4 files changed, 264 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 97ceb0f2e539..e440a9d5cca2 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3076,6 +3076,34 @@ union bpf_attr {
* See: clock_gettime(CLOCK_BOOTTIME)
* Return
* Current *ktime*.
+ *
+ * int bpf_seq_printf(struct seq_file *m, const char *fmt, u32 fmt_size, const void *data, u32 data_len)
+ * Description
+ * seq_printf uses seq_file seq_printf() to print out the format string.
+ * The *m* represents the seq_file. The *fmt* and *fmt_size* are for
+ * the format string itself. The *data* and *data_len* are format string
+ * arguments. The *data* are a u64 array and corresponding format string
+ * values are stored in the array. For strings and pointers where pointees
+ * are accessed, only the pointer values are stored in the *data* array.
+ * The *data_len* is the *data* size in term of bytes.
+ * Return
+ * 0 on success, or a negative errno in case of failure.
+ *
+ * * **-EBUSY** Percpu memory copy buffer is busy, can try again
+ * by returning 1 from bpf program.
+ * * **-EINVAL** Invalid arguments, or invalid/unsupported formats.
+ * * **-E2BIG** Too many format specifiers.
+ * * **-EOVERFLOW** Overflow happens, the same object will be tried again.
+ *
+ * int bpf_seq_write(struct seq_file *m, const void *data, u32 len)
+ * Description
+ * seq_write uses seq_file seq_write() to write the data.
+ * The *m* represents the seq_file. The *data* and *len* represent the
+ * data to write in bytes.
+ * Return
+ * 0 on success, or a negative errno in case of failure.
+ *
+ * * **-EOVERFLOW** Overflow happens, the same object will be tried again.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3203,7 +3231,9 @@ union bpf_attr {
FN(get_netns_cookie), \
FN(get_current_ancestor_cgroup_id), \
FN(sk_assign), \
- FN(ktime_get_boot_ns),
+ FN(ktime_get_boot_ns), \
+ FN(seq_printf), \
+ FN(seq_write),

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index e875c95d3ced..02721cbaa2f8 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -457,6 +457,198 @@ const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
return &bpf_trace_printk_proto;
}

+#define MAX_SEQ_PRINTF_VARARGS 12
+#define MAX_SEQ_PRINTF_MAX_MEMCPY 6
+#define MAX_SEQ_PRINTF_STR_LEN 128
+
+struct bpf_seq_printf_buf {
+ char buf[MAX_SEQ_PRINTF_MAX_MEMCPY][MAX_SEQ_PRINTF_STR_LEN];
+};
+static DEFINE_PER_CPU(struct bpf_seq_printf_buf, bpf_seq_printf_buf);
+static DEFINE_PER_CPU(int, bpf_seq_printf_buf_used);
+
+BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size,
+ const void *, data, u32, data_len)
+{
+ int err = -EINVAL, fmt_cnt = 0, memcpy_cnt = 0;
+ int i, buf_used, copy_size, num_args;
+ u64 params[MAX_SEQ_PRINTF_VARARGS];
+ struct bpf_seq_printf_buf *bufs;
+ const u64 *args = data;
+
+ buf_used = this_cpu_inc_return(bpf_seq_printf_buf_used);
+ if (WARN_ON_ONCE(buf_used > 1)) {
+ err = -EBUSY;
+ goto out;
+ }
+
+ bufs = this_cpu_ptr(&bpf_seq_printf_buf);
+
+ /*
+ * bpf_check()->check_func_arg()->check_stack_boundary()
+ * guarantees that fmt points to bpf program stack,
+ * fmt_size bytes of it were initialized and fmt_size > 0
+ */
+ if (fmt[--fmt_size] != 0)
+ goto out;
+
+ if (data_len & 7)
+ goto out;
+
+ for (i = 0; i < fmt_size; i++) {
+ if (fmt[i] == '%') {
+ if (fmt[i + 1] == '%')
+ i++;
+ else if (!data || !data_len)
+ goto out;
+ }
+ }
+
+ num_args = data_len / 8;
+
+ /* check format string for allowed specifiers */
+ for (i = 0; i < fmt_size; i++) {
+ /* only printable ascii for now. */
+ if ((!isprint(fmt[i]) && !isspace(fmt[i])) || !isascii(fmt[i]))
+ goto out;
+
+ if (fmt[i] != '%')
+ continue;
+
+ if (fmt[i + 1] == '%') {
+ i++;
+ continue;
+ }
+
+ if (fmt_cnt >= MAX_SEQ_PRINTF_VARARGS) {
+ err = -E2BIG;
+ goto out;
+ }
+
+ if (fmt_cnt >= num_args)
+ goto out;
+
+ /* fmt[i] != 0 && fmt[last] == 0, so we can access fmt[i + 1] */
+ i++;
+
+ /* skip optional "[0 +-][num]" width formating field */
+ while (fmt[i] == '0' || fmt[i] == '+' || fmt[i] == '-' ||
+ fmt[i] == ' ')
+ i++;
+ if (fmt[i] >= '1' && fmt[i] <= '9') {
+ i++;
+ while (fmt[i] >= '0' && fmt[i] <= '9')
+ i++;
+ }
+
+ if (fmt[i] == 's') {
+ /* try our best to copy */
+ if (memcpy_cnt >= MAX_SEQ_PRINTF_MAX_MEMCPY) {
+ err = -E2BIG;
+ goto out;
+ }
+
+ bufs->buf[memcpy_cnt][0] = 0;
+ strncpy_from_unsafe(bufs->buf[memcpy_cnt],
+ (void *) (long) args[fmt_cnt],
+ MAX_SEQ_PRINTF_STR_LEN);
+ params[fmt_cnt] = (u64)(long)bufs->buf[memcpy_cnt];
+
+ fmt_cnt++;
+ memcpy_cnt++;
+ continue;
+ }
+
+ if (fmt[i] == 'p') {
+ if (fmt[i + 1] == 0 ||
+ fmt[i + 1] == 'K' ||
+ fmt[i + 1] == 'x') {
+ /* just kernel pointers */
+ params[fmt_cnt] = args[fmt_cnt];
+ fmt_cnt++;
+ continue;
+ }
+
+ /* only support "%pI4", "%pi4", "%pI6" and "pi6". */
+ if (fmt[i + 1] != 'i' && fmt[i + 1] != 'I')
+ goto out;
+ if (fmt[i + 2] != '4' && fmt[i + 2] != '6')
+ goto out;
+
+ if (memcpy_cnt >= MAX_SEQ_PRINTF_MAX_MEMCPY) {
+ err = -E2BIG;
+ goto out;
+ }
+
+
+ copy_size = (fmt[i + 2] == '4') ? 4 : 16;
+
+ probe_kernel_read(bufs->buf[memcpy_cnt],
+ (void *) (long) args[fmt_cnt], copy_size);
+ params[fmt_cnt] = (u64)(long)bufs->buf[memcpy_cnt];
+
+ i += 2;
+ fmt_cnt++;
+ memcpy_cnt++;
+ continue;
+ }
+
+ if (fmt[i] == 'l') {
+ i++;
+ if (fmt[i] == 'l')
+ i++;
+ }
+
+ if (fmt[i] != 'i' && fmt[i] != 'd' &&
+ fmt[i] != 'u' && fmt[i] != 'x')
+ goto out;
+
+ params[fmt_cnt] = args[fmt_cnt];
+ fmt_cnt++;
+ }
+
+ /* Maximumly we can have MAX_SEQ_PRINTF_VARARGS parameter, just give
+ * all of them to seq_printf().
+ */
+ seq_printf(m, fmt, params[0], params[1], params[2], params[3],
+ params[4], params[5], params[6], params[7], params[8],
+ params[9], params[10], params[11]);
+
+ err = seq_has_overflowed(m) ? -EOVERFLOW : 0;
+out:
+ this_cpu_dec(bpf_seq_printf_buf_used);
+ return err;
+}
+
+static int bpf_seq_printf_btf_ids[5];
+static const struct bpf_func_proto bpf_seq_printf_proto = {
+ .func = bpf_seq_printf,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_BTF_ID,
+ .arg2_type = ARG_PTR_TO_MEM,
+ .arg3_type = ARG_CONST_SIZE,
+ .arg4_type = ARG_PTR_TO_MEM_OR_NULL,
+ .arg5_type = ARG_CONST_SIZE_OR_ZERO,
+ .btf_id = bpf_seq_printf_btf_ids,
+};
+
+BPF_CALL_3(bpf_seq_write, struct seq_file *, m, const void *, data, u32, len)
+{
+ return seq_write(m, data, len) ? -EOVERFLOW : 0;
+}
+
+static int bpf_seq_write_btf_ids[5];
+static const struct bpf_func_proto bpf_seq_write_proto = {
+ .func = bpf_seq_write,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_BTF_ID,
+ .arg2_type = ARG_PTR_TO_MEM,
+ .arg3_type = ARG_CONST_SIZE_OR_ZERO,
+ .btf_id = bpf_seq_write_btf_ids,
+};
+
static __always_inline int
get_map_perf_counter(struct bpf_map *map, u64 flags,
u64 *value, u64 *enabled, u64 *running)
@@ -1226,6 +1418,14 @@ tracing_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
case BPF_FUNC_xdp_output:
return &bpf_xdp_output_proto;
#endif
+ case BPF_FUNC_seq_printf:
+ return prog->expected_attach_type == BPF_TRACE_ITER ?
+ &bpf_seq_printf_proto :
+ NULL;
+ case BPF_FUNC_seq_write:
+ return prog->expected_attach_type == BPF_TRACE_ITER ?
+ &bpf_seq_write_proto :
+ NULL;
default:
return raw_tp_prog_func_proto(func_id, prog);
}
diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py
index f43d193aff3a..ded304c96a05 100755
--- a/scripts/bpf_helpers_doc.py
+++ b/scripts/bpf_helpers_doc.py
@@ -414,6 +414,7 @@ class PrinterHelpers(Printer):
'struct sk_reuseport_md',
'struct sockaddr',
'struct tcphdr',
+ 'struct seq_file',

'struct __sk_buff',
'struct sk_msg_md',
@@ -450,6 +451,7 @@ class PrinterHelpers(Printer):
'struct sk_reuseport_md',
'struct sockaddr',
'struct tcphdr',
+ 'struct seq_file',
}
mapped_types = {
'u8': '__u8',
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 97ceb0f2e539..e440a9d5cca2 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3076,6 +3076,34 @@ union bpf_attr {
* See: clock_gettime(CLOCK_BOOTTIME)
* Return
* Current *ktime*.
+ *
+ * int bpf_seq_printf(struct seq_file *m, const char *fmt, u32 fmt_size, const void *data, u32 data_len)
+ * Description
+ * seq_printf uses seq_file seq_printf() to print out the format string.
+ * The *m* represents the seq_file. The *fmt* and *fmt_size* are for
+ * the format string itself. The *data* and *data_len* are format string
+ * arguments. The *data* are a u64 array and corresponding format string
+ * values are stored in the array. For strings and pointers where pointees
+ * are accessed, only the pointer values are stored in the *data* array.
+ * The *data_len* is the *data* size in term of bytes.
+ * Return
+ * 0 on success, or a negative errno in case of failure.
+ *
+ * * **-EBUSY** Percpu memory copy buffer is busy, can try again
+ * by returning 1 from bpf program.
+ * * **-EINVAL** Invalid arguments, or invalid/unsupported formats.
+ * * **-E2BIG** Too many format specifiers.
+ * * **-EOVERFLOW** Overflow happens, the same object will be tried again.
+ *
+ * int bpf_seq_write(struct seq_file *m, const void *data, u32 len)
+ * Description
+ * seq_write uses seq_file seq_write() to write the data.
+ * The *m* represents the seq_file. The *data* and *len* represent the
+ * data to write in bytes.
+ * Return
+ * 0 on success, or a negative errno in case of failure.
+ *
+ * * **-EOVERFLOW** Overflow happens, the same object will be tried again.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3203,7 +3231,9 @@ union bpf_attr {
FN(get_netns_cookie), \
FN(get_current_ancestor_cgroup_id), \
FN(sk_assign), \
- FN(ktime_get_boot_ns),
+ FN(ktime_get_boot_ns), \
+ FN(seq_printf), \
+ FN(seq_write),

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
--
2.24.1