[PATCH bpf-next 1/6] libbpf: Sanitize BTF_KIND_FUNC linkage

Alexei Starovoitov
2020-01-08T07:26:01Z

In case kernel doesn't support static/global/extern liknage of BTF_KIND_FUNC
sanitize BTF produced by llvm.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
tools/include/uapi/linux/btf.h | 6 ++++++
tools/lib/bpf/libbpf.c | 35 +++++++++++++++++++++++++++++++++-
2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h
index 1a2898c482ee..5a667107ad2c 100644
--- a/tools/include/uapi/linux/btf.h
+++ b/tools/include/uapi/linux/btf.h
@@ -146,6 +146,12 @@ enum {
BTF_VAR_GLOBAL_EXTERN = 2,
};

+enum btf_func_linkage {
+ BTF_FUNC_STATIC = 0,
+ BTF_FUNC_GLOBAL = 1,
+ BTF_FUNC_EXTERN = 2,
+};
+
/* BTF_KIND_VAR is followed by a single "struct btf_var" to describe
* additional information related to the variable such as its linkage.
*/
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 7513165b104f..f72b3ed6c34b 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -166,6 +166,8 @@ struct bpf_capabilities {
__u32 btf_datasec:1;
/* BPF_F_MMAPABLE is supported for arrays */
__u32 array_mmap:1;
+ /* static/global/extern is supported for BTF_KIND_FUNC */
+ __u32 btf_func_linkage:1;
};

enum reloc_type {
@@ -1817,13 +1819,14 @@ static bool section_have_execinstr(struct bpf_object *obj, int idx)

static void bpf_object__sanitize_btf(struct bpf_object *obj)
{
+ bool has_func_linkage = obj->caps.btf_func_linkage;
bool has_datasec = obj->caps.btf_datasec;
bool has_func = obj->caps.btf_func;
struct btf *btf = obj->btf;
struct btf_type *t;
int i, j, vlen;

- if (!obj->btf || (has_func && has_datasec))
+ if (!obj->btf || (has_func && has_datasec && has_func_linkage))
return;

for (i = 1; i <= btf__get_nr_types(btf); i++) {
@@ -1871,6 +1874,9 @@ static void bpf_object__sanitize_btf(struct bpf_object *obj)
} else if (!has_func && btf_is_func(t)) {
/* replace FUNC with TYPEDEF */
t->info = BTF_INFO_ENC(BTF_KIND_TYPEDEF, 0, 0);
+ } else if (!has_func_linkage && btf_is_func(t)) {
+ /* replace BTF_FUNC_GLOBAL with BTF_FUNC_STATIC */
+ t->info = BTF_INFO_ENC(BTF_KIND_FUNC, 0, 0);
}
}
}
@@ -2804,6 +2810,32 @@ static int bpf_object__probe_btf_func(struct bpf_object *obj)
return 0;
}

+static int bpf_object__probe_btf_func_linkage(struct bpf_object *obj)
+{
+ static const char strs[] = "\0int\0x\0a";
+ /* static void x(int a) {} */
+ __u32 types[] = {
+ /* int */
+ BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
+ /* FUNC_PROTO */ /* [2] */
+ BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 1), 0),
+ BTF_PARAM_ENC(7, 1),
+ /* FUNC x BTF_FUNC_GLOBAL */ /* [3] */
+ BTF_TYPE_ENC(5, BTF_INFO_ENC(BTF_KIND_FUNC, 0, 1), 2),
+ };
+ int btf_fd;
+
+ btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types),
+ strs, sizeof(strs));
+ if (btf_fd >= 0) {
+ obj->caps.btf_func_linkage = 1;
+ close(btf_fd);
+ return 1;
+ }
+
+ return 0;
+}
+
static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
{
static const char strs[] = "\0x\0.data";
@@ -2859,6 +2891,7 @@ bpf_object__probe_caps(struct bpf_object *obj)
bpf_object__probe_name,
bpf_object__probe_global_data,
bpf_object__probe_btf_func,
+ bpf_object__probe_btf_func_linkage,
bpf_object__probe_btf_datasec,
bpf_object__probe_array_mmap,
};
--
2.23.0