Allow bpf_object__open() to access files of either endianness, and convert
included BPF programs to native byte-order in-memory for introspection.
Loading BPF objects of non-native byte-order is still disallowed however.
Signed-off-by: Tony Ambardar <tony.ambardar@xxxxxxxxx>
---
tools/lib/bpf/libbpf.c | 52 +++++++++++++++++++++++++++------
tools/lib/bpf/libbpf_internal.h | 11 +++++++
2 files changed, 54 insertions(+), 9 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0226d3b50709..46f41ea5e74d 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -694,6 +694,8 @@ struct bpf_object {
/* Information when doing ELF related work. Only valid if efile.elf is not NULL */
struct elf_state efile;
+ unsigned char byteorder;
+
struct btf *btf;
struct btf_ext *btf_ext;
@@ -940,6 +942,21 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
return 0;
}
+static void bpf_object_bswap_progs(struct bpf_object *obj)
+{
+ struct bpf_program *prog = obj->programs;
+ struct bpf_insn *insn;
+ int p, i;
+
+ for (p = 0; p < obj->nr_programs; p++, prog++) {
+ insn = prog->insns;
+ for (i = 0; i < prog->insns_cnt; i++, insn++)
+ bpf_insn_bswap(insn);
+ }
+ pr_debug("converted %zu BPF programs to native byte order\n",
+ obj->nr_programs);
+}
+
static const struct btf_member *
find_member_by_offset(const struct btf_type *t, __u32 bit_offset)
{
@@ -1506,6 +1523,7 @@ static void bpf_object__elf_finish(struct bpf_object *obj)
elf_end(obj->efile.elf);
obj->efile.elf = NULL;
+ obj->efile.ehdr = NULL;
obj->efile.symbols = NULL;
obj->efile.arena_data = NULL;
@@ -1571,6 +1589,16 @@ static int bpf_object__elf_init(struct bpf_object *obj)
goto errout;
}
+ /* Validate ELF object endianness... */
+ if (ehdr->e_ident[EI_DATA] != ELFDATA2LSB &&
+ ehdr->e_ident[EI_DATA] != ELFDATA2MSB) {
+ err = -LIBBPF_ERRNO__ENDIAN;
+ pr_warn("elf: '%s' has unknown byte order\n", obj->path);
+ goto errout;
+ }
+ /* and save after bpf_object_open() frees ELF data */
+ obj->byteorder = ehdr->e_ident[EI_DATA];
+
if (elf_getshdrstrndx(elf, &obj->efile.shstrndx)) {
pr_warn("elf: failed to get section names section index for %s: %s\n",
obj->path, elf_errmsg(-1));
@@ -1599,19 +1627,15 @@ static int bpf_object__elf_init(struct bpf_object *obj)
return err;
}
-static int bpf_object__check_endianness(struct bpf_object *obj)
+static bool is_native_endianness(struct bpf_object *obj)
{
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
- if (obj->efile.ehdr->e_ident[EI_DATA] == ELFDATA2LSB)
- return 0;
+ return obj->byteorder == ELFDATA2LSB;
#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
- if (obj->efile.ehdr->e_ident[EI_DATA] == ELFDATA2MSB)
- return 0;
+ return obj->byteorder == ELFDATA2MSB;
#else
# error "Unrecognized __BYTE_ORDER__"
#endif
- pr_warn("elf: endianness mismatch in %s.\n", obj->path);
- return -LIBBPF_ERRNO__ENDIAN;
}
static int
@@ -3953,6 +3977,10 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
return -LIBBPF_ERRNO__FORMAT;
}
+ /* change BPF program insns to native endianness for introspection */
+ if (!is_native_endianness(obj))
+ bpf_object_bswap_progs(obj);
+
/* sort BPF programs by section name and in-section instruction offset
* for faster search
*/
@@ -7992,7 +8020,6 @@ static struct bpf_object *bpf_object_open(const char *path, const void *obj_buf,
}
err = bpf_object__elf_init(obj);
- err = err ? : bpf_object__check_endianness(obj);
err = err ? : bpf_object__elf_collect(obj);
err = err ? : bpf_object__collect_externs(obj);
err = err ? : bpf_object_fixup_btf(obj);
@@ -8498,8 +8525,15 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
return libbpf_err(-EINVAL);
}
- if (obj->gen_loader)
+ /* Disallow kernel loading programs of non-native endianness but
+ * permit cross-endian creation of "light skeleton".
+ */
+ if (obj->gen_loader) {
bpf_gen__init(obj->gen_loader, extra_log_level, obj->nr_programs, obj->nr_maps);
+ } else if (!is_native_endianness(obj)) {
+ pr_warn("object '%s': loading non-native endianness is unsupported\n", obj->name);
+ return libbpf_err(-LIBBPF_ERRNO__ENDIAN);
+ }
err = bpf_object_prepare_token(obj);
err = err ? : bpf_object__probe_loading(obj);
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index a8531195acd4..eda7a0cc2b8c 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -11,6 +11,7 @@
#include <stdlib.h>
#include <limits.h>
+#include <byteswap.h>
#include <errno.h>
#include <linux/err.h>
#include <fcntl.h>
@@ -616,6 +617,16 @@ static inline bool is_ldimm64_insn(struct bpf_insn *insn)
return insn->code == (BPF_LD | BPF_IMM | BPF_DW);
}
+static inline void bpf_insn_bswap(struct bpf_insn *insn)
+{
+ __u8 tmp_reg = insn->dst_reg;
+
+ insn->dst_reg = insn->src_reg;
+ insn->src_reg = tmp_reg;
+ insn->off = bswap_16(insn->off);
+ insn->imm = bswap_32(insn->imm);
+}
+
/* Unconditionally dup FD, ensuring it doesn't use [0, 2] range.
* Original FD is not closed or altered in any other way.
* Preserves original FD value, if it's invalid (negative).
--
2.34.1
