[PATCH v2 2/4] bpf: Add support for reading kernel pointers

["Joel Fernandes (Google)" <joel@joelfernandes.org>]

The bpf_probe_read function is ambiguous in whether the pointer being
read is a kernel or user one. Add a specific function for kernel pointer
in this patch. Previous patches add it for userspace pointers.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 include/uapi/linux/bpf.h |  9 ++++++++-
 kernel/trace/bpf_trace.c | 22 ++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 8146784b9fe3..05af4e1151d3 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2437,6 +2437,12 @@ union bpf_attr {
  *             Read a userspace pointer safely.
  *     Return
  *             0 on success or negative error
+ *
+ * int bpf_probe_read_kernel(void *dst, int size, void *src)
+ *     Description
+ *             Read a kernel pointer safely.
+ *     Return
+ *             0 on success or negative error
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -2538,7 +2544,8 @@ union bpf_attr {
 	FN(tcp_sock),			\
 	FN(skb_ecn_set_ce),		\
 	FN(get_listener_sock),		\
-	FN(probe_read_user),
+	FN(probe_read_user),		\
+	FN(probe_read_kernel),
 
 /* 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 7485deb0777f..99dc354fd62b 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -153,6 +153,26 @@ static const struct bpf_func_proto bpf_probe_read_proto = {
 	.arg3_type	= ARG_ANYTHING,
 };
 
+BPF_CALL_3(bpf_probe_read_kernel, void *, dst, u32, size, const void *, unsafe_ptr)
+{
+	int ret;
+
+	ret = probe_kernel_read(dst, unsafe_ptr, size);
+	if (unlikely(ret < 0))
+		memset(dst, 0, size);
+
+	return ret;
+}
+
+static const struct bpf_func_proto bpf_probe_read_kernel_proto = {
+	.func		= bpf_probe_read_kernel,
+	.gpl_only	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_UNINIT_MEM,
+	.arg2_type	= ARG_CONST_SIZE_OR_ZERO,
+	.arg3_type	= ARG_ANYTHING,
+};
+
 BPF_CALL_3(bpf_probe_read_user, void *, dst, u32, size, const void *, unsafe_ptr)
 {
 	int ret;
@@ -593,6 +613,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_probe_read_proto;
 	case BPF_FUNC_probe_read_user:
 		return &bpf_probe_read_user_proto;
+	case BPF_FUNC_probe_read_kernel:
+		return &bpf_probe_read_kernel_proto;
 	case BPF_FUNC_ktime_get_ns:
 		return &bpf_ktime_get_ns_proto;
 	case BPF_FUNC_tail_call:
-- 
2.21.0.1020.gf2820cf01a-goog