netdev - [PATCH bpf-next 2/2] libbpf: reject static maps

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Date:   Thu, 13 May 2021 15:55:52 -0700
From:   Andrii Nakryiko <andrii@...nel.org>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>
CC:     <andrii@...nel.org>, <kernel-team@...com>
Subject: [PATCH bpf-next 2/2] libbpf: reject static maps

Static maps never really worked with libbpf, because all such maps were always
silently resolved to the very first map. Detect static maps (both legacy and
BTF-defined) and report user-friendly error.

Tested locally by switching few maps (legacy and BTF-defined) in selftests to
static ones and verifying that now libbpf rejects them loudly.

Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
---
 tools/lib/bpf/libbpf.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b8cf93fa1b4d..ac5ab903d42b 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1795,7 +1795,6 @@ static int bpf_object__init_user_maps(struct bpf_object *obj, bool strict)
 	if (!symbols)
 		return -EINVAL;
 
-
 	scn = elf_sec_by_idx(obj, obj->efile.maps_shndx);
 	data = elf_sec_data(obj, scn);
 	if (!scn || !data) {
@@ -1848,6 +1847,7 @@ static int bpf_object__init_user_maps(struct bpf_object *obj, bool strict)
 		if (IS_ERR(map))
 			return PTR_ERR(map);
 
+
 		map_name = elf_sym_str(obj, sym.st_name);
 		if (!map_name) {
 			pr_warn("failed to get map #%d name sym string for obj %s\n",
@@ -1855,6 +1855,12 @@ static int bpf_object__init_user_maps(struct bpf_object *obj, bool strict)
 			return -LIBBPF_ERRNO__FORMAT;
 		}
 
+		if (GELF_ST_TYPE(sym.st_info) == STT_SECTION
+		    || GELF_ST_BIND(sym.st_info) == STB_LOCAL) {
+			pr_warn("map '%s' (legacy): static maps are not supported\n", map_name);
+			return -ENOTSUP;
+		}
+
 		map->libbpf_type = LIBBPF_MAP_UNSPEC;
 		map->sec_idx = sym.st_shndx;
 		map->sec_offset = sym.st_value;
@@ -2262,6 +2268,16 @@ static void fill_map_from_def(struct bpf_map *map, const struct btf_map_def *def
 		pr_debug("map '%s': found inner map definition.\n", map->name);
 }
 
+static const char *btf_var_linkage_str(__u32 linkage)
+{
+	switch (linkage) {
+	case BTF_VAR_STATIC: return "static";
+	case BTF_VAR_GLOBAL_ALLOCATED: return "global";
+	case BTF_VAR_GLOBAL_EXTERN: return "extern";
+	default: return "unknown";
+	}
+}
+
 static int bpf_object__init_user_btf_map(struct bpf_object *obj,
 					 const struct btf_type *sec,
 					 int var_idx, int sec_idx,
@@ -2294,10 +2310,9 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
 			map_name, btf_kind_str(var));
 		return -EINVAL;
 	}
-	if (var_extra->linkage != BTF_VAR_GLOBAL_ALLOCATED &&
-	    var_extra->linkage != BTF_VAR_STATIC) {
-		pr_warn("map '%s': unsupported var linkage %u.\n",
-			map_name, var_extra->linkage);
+	if (var_extra->linkage != BTF_VAR_GLOBAL_ALLOCATED) {
+		pr_warn("map '%s': unsupported map linkage %s.\n",
+			map_name, btf_var_linkage_str(var_extra->linkage));
 		return -EOPNOTSUPP;
 	}
 
-- 
2.30.2