Commit bcc60abd authored by Tony Ambardar's avatar Tony Ambardar Committed by Alexei Starovoitov
Browse files

libbpf: Support opening bpf objects of either endianness 



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: default avatarTony Ambardar <tony.ambardar@gmail.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/26353c1a1887a54400e1acd6c138fa90c99cdd40.1726475448.git.tony.ambardar@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent cf579164

tools/lib/bpf/libbpf.c

+42 −9
Original line number Diff line number Diff line
@@ -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 +942,20 @@ 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 +1522,7 @@ 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 +1588,16 @@ 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 +1626,15 @@ 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
@@ -3954,6 +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

	 */
@@ -7997,7 +8024,6 @@ 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);
@@ -8503,8 +8529,15 @@ 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);

tools/lib/bpf/libbpf_internal.h

+10 −0
Original line number Diff line number Diff line
@@ -617,6 +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).