[PATCH 08/11] bpf: Add BTF whitelist support

[Jiri Olsa <jolsa@kernel.org>]

Adding support to define 'whitelist' of BTF IDs, which is
also sorted.

Following defines sorted list of BTF IDs that is accessible
within kernel code as btf_whitelist_d_path and its count is
in btf_whitelist_d_path_cnt variable.

  extern int btf_whitelist_d_path[];
  extern int btf_whitelist_d_path_cnt;

  BTF_WHITELIST_ENTRY(btf_whitelist_d_path)
  BTF_ID(func, vfs_truncate)
  BTF_ID(func, vfs_fallocate)
  BTF_ID(func, dentry_open)
  BTF_ID(func, vfs_getattr)
  BTF_ID(func, filp_close)
  BTF_WHITELIST_END(btf_whitelist_d_path)

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 include/linux/bpf.h   |  3 +++
 kernel/bpf/btf.c      | 13 +++++++++++++
 kernel/bpf/btf_ids.h  | 38 ++++++++++++++++++++++++++++++++++++++
 kernel/bpf/verifier.c |  5 +++++
 4 files changed, 59 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index e98c113a5d27..a94e85c2ec50 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -283,6 +283,7 @@ struct bpf_func_proto {
 		enum bpf_arg_type arg_type[5];
 	};
 	int *btf_id; /* BTF ids of arguments */
+	bool (*allowed)(const struct bpf_prog *prog);
 };
 
 /* bpf_context is intentionally undefined structure. Pointer to bpf_context is
@@ -1745,6 +1746,8 @@ enum bpf_text_poke_type {
 int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
 		       void *addr1, void *addr2);
 
+bool btf_whitelist_search(int id, int list[], int cnt);
+
 extern int bpf_skb_output_btf_ids[];
 extern int bpf_seq_printf_btf_ids[];
 extern int bpf_seq_write_btf_ids[];
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 6924180a19c4..feda74d232c5 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -20,6 +20,7 @@
 #include <linux/btf.h>
 #include <linux/skmsg.h>
 #include <linux/perf_event.h>
+#include <linux/bsearch.h>
 #include <net/sock.h>
 
 /* BTF (BPF Type Format) is the meta data format which describes
@@ -4669,3 +4670,15 @@ u32 btf_id(const struct btf *btf)
 {
 	return btf->id;
 }
+
+static int btf_id_cmp_func(const void *a, const void *b)
+{
+	const int *pa = a, *pb = b;
+
+	return *pa - *pb;
+}
+
+bool btf_whitelist_search(int id, int list[], int cnt)
+{
+	return bsearch(&id, list, cnt, sizeof(int), btf_id_cmp_func) != NULL;
+}
diff --git a/kernel/bpf/btf_ids.h b/kernel/bpf/btf_ids.h
index 68aa5c38a37f..a90c09faa515 100644
--- a/kernel/bpf/btf_ids.h
+++ b/kernel/bpf/btf_ids.h
@@ -67,4 +67,42 @@ asm(							\
 #name ":;                                      \n"	\
 ".popsection;                                  \n");
 
+
+/*
+ * The BTF_WHITELIST_ENTRY/END macros pair defines sorted
+ * list of BTF IDs plus its members count, with following
+ * layout:
+ *
+ * BTF_WHITELIST_ENTRY(list2)
+ * BTF_ID(type1, name1)
+ * BTF_ID(type2, name2)
+ * BTF_WHITELIST_END(list)
+ *
+ * __BTF_ID__sort__list:
+ * list2_cnt:
+ * .zero 4
+ * list2:
+ * __BTF_ID__type1__name1__3:
+ * .zero 4
+ * __BTF_ID__type2__name2__4:
+ * .zero 4
+ *
+ */
+#define BTF_WHITELIST_ENTRY(name)			\
+asm(							\
+".pushsection " SECTION ",\"a\";               \n"	\
+".global __BTF_ID__sort__" #name ";            \n"	\
+"__BTF_ID__sort__" #name ":;                   \n"	\
+".global " #name "_cnt;                        \n"	\
+#name "_cnt:;                                  \n"	\
+".zero 4                                       \n"	\
+".popsection;                                  \n");	\
+BTF_ID_LIST(name)
+
+#define BTF_WHITELIST_END(name)				\
+asm(							\
+".pushsection " SECTION ",\"a\";              \n"	\
+".size __BTF_ID__sort__" #name ", .-" #name " \n"	\
+".popsection;                                 \n");
+
 #endif
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index bee3da2cd945..5a9a6fd72907 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4633,6 +4633,11 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
 		return -EINVAL;
 	}
 
+	if (fn->allowed && !fn->allowed(env->prog)) {
+		verbose(env, "helper call is not allowed in probe\n");
+		return -EINVAL;
+	}
+
 	/* With LD_ABS/IND some JITs save/restore skb from r1. */
 	changes_data = bpf_helper_changes_pkt_data(fn->func);
 	if (changes_data && fn->arg1_type != ARG_PTR_TO_CTX) {
-- 
2.25.4