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libbpf: Support opening bpf objects of either endianness

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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@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/26353c1a1887a54400e1acd6c138fa90c99cdd40.1726475448.git.tony.ambardar@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Tony Ambardar
2024-09-16 01:37:44 -07:00
committed by Alexei Starovoitov
parent cf579164e9
commit bcc60abd67
2 changed files with 52 additions and 9 deletions
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51
tools/lib/bpf/libbpf.c
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@@ -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 @@ errout:
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);