[PATCH 1/1] tracing, bpf: Implement function bpf_probe_write

[Sargun Dhillon]

Provides BPF programs, attached to kprobes a safe way to write to
memory referenced by probes. This is done by making probe_kernel_write
accessible to bpf functions via the bpf_probe_write helper.

Signed-off-by: Sargun Dhillon <sargun@xxxxxxxxx>
---
 include/uapi/linux/bpf.h  |  3 +++
 kernel/trace/bpf_trace.c  | 20 ++++++++++++++++++++
 samples/bpf/bpf_helpers.h |  2 ++
 3 files changed, 25 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 406459b..355b565 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -313,6 +313,9 @@ enum bpf_func_id {
  */
  BPF_FUNC_skb_get_tunnel_opt,
  BPF_FUNC_skb_set_tunnel_opt,
+
+ BPF_FUNC_probe_write, /* int bpf_probe_write(void *dst, void *src,
int size) */
+
  __BPF_FUNC_MAX_ID,
 };

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 26f603d..dc745d1 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -81,6 +81,24 @@ static const struct bpf_func_proto bpf_probe_read_proto = {
  .arg3_type = ARG_ANYTHING,
 };

+static u64 bpf_probe_write(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+ void *dst = (void *) (long) r1;
+ void *unsafe_ptr = (void *) (long) r2;
+ int  size = (int) r3;
+
+ return probe_kernel_write(dst, unsafe_ptr, size);
+}
+
+static const struct bpf_func_proto bpf_probe_write_proto = {
+ .func = bpf_probe_write,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_ANYTHING,
+ .arg2_type = ARG_PTR_TO_RAW_STACK,
+ .arg3_type = ARG_CONST_STACK_SIZE,
+};
+
 /*
  * limited trace_printk()
  * only %d %u %x %ld %lu %lx %lld %llu %llx %p %s conversion specifiers allowed
@@ -319,6 +337,8 @@ static const struct bpf_func_proto
*tracing_func_proto(enum bpf_func_id func_id)
  return &bpf_map_delete_elem_proto;
  case BPF_FUNC_probe_read:
  return &bpf_probe_read_proto;
+ case BPF_FUNC_probe_write:
+ return &bpf_probe_write_proto;
  case BPF_FUNC_ktime_get_ns:
  return &bpf_ktime_get_ns_proto;
  case BPF_FUNC_tail_call:
diff --git a/samples/bpf/bpf_helpers.h b/samples/bpf/bpf_helpers.h
index 7904a2a..07b90ac 100644
--- a/samples/bpf/bpf_helpers.h
+++ b/samples/bpf/bpf_helpers.h
@@ -17,6 +17,8 @@ static int (*bpf_map_delete_elem)(void *map, void *key) =
  (void *) BPF_FUNC_map_delete_elem;
 static int (*bpf_probe_read)(void *dst, int size, void *unsafe_ptr) =
  (void *) BPF_FUNC_probe_read;
+static int (*bpf_probe_write)(void *dst, void *unsafe_ptr, int size) =
+ (void *) BPF_FUNC_probe_write;
 static unsigned long long (*bpf_ktime_get_ns)(void) =
  (void *) BPF_FUNC_ktime_get_ns;
 static int (*bpf_trace_printk)(const char *fmt, int fmt_size, ...) =
-- 
2.7.4