bpf: Check types of arguments passed into helpers

Introduce new helper that reuses existing skb perf_event output
implementation, but can be called from raw_tracepoint programs
that receive 'struct sk_buff *' as tracepoint argument or
can walk other kernel data structures to skb pointer.

In order to do that teach verifier to resolve true C types
of bpf helpers into in-kernel BTF ids.
The type of kernel pointer passed by raw tracepoint into bpf
program will be tracked by the verifier all the way until
it's passed into helper function.
For example:
kfree_skb() kernel function calls trace_kfree_skb(skb, loc);
bpf programs receives that skb pointer and may eventually
pass it into bpf_skb_output() bpf helper which in-kernel is
implemented via bpf_skb_event_output() kernel function.
Its first argument in the kernel is 'struct sk_buff *'.
The verifier makes sure that types match all the way.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20191016032505.2089704-11-ast@kernel.org

1 files changed, 13 insertions, 5 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a7330d75bb94..2c2c29b49845 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -213,6 +213,7 @@ enum bpf_arg_type {
 	ARG_PTR_TO_INT,		/* pointer to int */
 	ARG_PTR_TO_LONG,	/* pointer to long */
 	ARG_PTR_TO_SOCKET,	/* pointer to bpf_sock (fullsock) */
+	ARG_PTR_TO_BTF_ID,	/* pointer to in-kernel struct */
 };
 
 /* type of values returned from helper functions */
@@ -235,11 +236,17 @@ struct bpf_func_proto {
 	bool gpl_only;
 	bool pkt_access;
 	enum bpf_return_type ret_type;
-	enum bpf_arg_type arg1_type;
-	enum bpf_arg_type arg2_type;
-	enum bpf_arg_type arg3_type;
-	enum bpf_arg_type arg4_type;
-	enum bpf_arg_type arg5_type;
+	union {
+		struct {
+			enum bpf_arg_type arg1_type;
+			enum bpf_arg_type arg2_type;
+			enum bpf_arg_type arg3_type;
+			enum bpf_arg_type arg4_type;
+			enum bpf_arg_type arg5_type;
+		};
+		enum bpf_arg_type arg_type[5];
+	};
+	u32 *btf_id; /* BTF ids of arguments */
 };
 
 /* bpf_context is intentionally undefined structure. Pointer to bpf_context is
@@ -765,6 +772,7 @@ int btf_struct_access(struct bpf_verifier_log *log,
 		      const struct btf_type *t, int off, int size,
 		      enum bpf_access_type atype,
 		      u32 *next_btf_id);
+u32 btf_resolve_helper_id(struct bpf_verifier_log *log, void *, int);
 
 #else /* !CONFIG_BPF_SYSCALL */
 static inline struct bpf_prog *bpf_prog_get(u32 ufd)