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libbpf: Always specify expected_attach_type on program load if supported

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For some types of BPF programs that utilize expected_attach_type, libbpf won't
set load_attr.expected_attach_type, even if expected_attach_type is known from
section definition. This was done to preserve backwards compatibility with old
kernels that didn't recognize expected_attach_type attribute yet (which was
added in 5e43f899b0 ("bpf: Check attach type at prog load time"). But this
is problematic for some BPF programs that utilize newer features that require
kernel to know specific expected_attach_type (e.g., extended set of return
codes for cgroup_skb/egress programs).

This patch makes libbpf specify expected_attach_type by default, but also
detect support for this field in kernel and not set it during program load.
This allows to have a good metadata for bpf_program
(e.g., bpf_program__get_extected_attach_type()), but still work with old
kernels (for cases where it can work at all).

Additionally, due to expected_attach_type being always set for recognized
program types, bpf_program__attach_cgroup doesn't have to do extra checks to
determine correct attach type, so remove that additional logic.

Also adjust section_names selftest to account for this change.

More detailed discussion can be found in [0].

  [0] https://lore.kernel.org/bpf/20200412003604.GA15986@rdna-mbp.dhcp.thefacebook.com/

Fixes: 5cf1e91456 ("bpf: cgroup inet skb programs can return 0 to 3")
Fixes: 5e43f899b0 ("bpf: Check attach type at prog load time")
Reported-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Andrey Ignatov <rdna@fb.com>
Link: https://lore.kernel.org/bpf/20200414182645.1368174-1-andriin@fb.com
This commit is contained in:
Andrii Nakryiko
2020-04-14 11:26:45 -07:00
committed by Daniel Borkmann
parent 99e3a236dd
commit 25498a1969
2 changed files with 109 additions and 59 deletions
Download Patch File Download Diff File Expand all files Collapse all files

126
tools/lib/bpf/libbpf.c
View File

@@ -178,6 +178,8 @@ struct bpf_capabilities {
__u32 array_mmap:1;
/* BTF_FUNC_GLOBAL is supported */
__u32 btf_func_global:1;
/* kernel support for expected_attach_type in BPF_PROG_LOAD */
__u32 exp_attach_type:1;
};
enum reloc_type {
@@ -194,6 +196,22 @@ struct reloc_desc {
int sym_off;
};
struct bpf_sec_def;
typedef struct bpf_link *(*attach_fn_t)(const struct bpf_sec_def *sec,
struct bpf_program *prog);
struct bpf_sec_def {
const char *sec;
size_t len;
enum bpf_prog_type prog_type;
enum bpf_attach_type expected_attach_type;
bool is_exp_attach_type_optional;
bool is_attachable;
bool is_attach_btf;
attach_fn_t attach_fn;
};
/*
* bpf_prog should be a better name but it has been used in
* linux/filter.h.
@@ -204,6 +222,7 @@ struct bpf_program {
char *name;
int prog_ifindex;
char *section_name;
const struct bpf_sec_def *sec_def;
/* section_name with / replaced by _; makes recursive pinning
* in bpf_object__pin_programs easier
*/
@@ -3315,6 +3334,37 @@ static int bpf_object__probe_array_mmap(struct bpf_object *obj)
return 0;
}
static int
bpf_object__probe_exp_attach_type(struct bpf_object *obj)
{
struct bpf_load_program_attr attr;
struct bpf_insn insns[] = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
};
int fd;
memset(&attr, 0, sizeof(attr));
/* use any valid combination of program type and (optional)
* non-zero expected attach type (i.e., not a BPF_CGROUP_INET_INGRESS)
* to see if kernel supports expected_attach_type field for
* BPF_PROG_LOAD command
*/
attr.prog_type = BPF_PROG_TYPE_CGROUP_SOCK;
attr.expected_attach_type = BPF_CGROUP_INET_SOCK_CREATE;
attr.insns = insns;
attr.insns_cnt = ARRAY_SIZE(insns);
attr.license = "GPL";
fd = bpf_load_program_xattr(&attr, NULL, 0);
if (fd >= 0) {
obj->caps.exp_attach_type = 1;
close(fd);
return 1;
}
return 0;
}
static int
bpf_object__probe_caps(struct bpf_object *obj)
{
@@ -3325,6 +3375,7 @@ bpf_object__probe_caps(struct bpf_object *obj)
bpf_object__probe_btf_func_global,
bpf_object__probe_btf_datasec,
bpf_object__probe_array_mmap,
bpf_object__probe_exp_attach_type,
};
int i, ret;
@@ -4861,7 +4912,12 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
memset(&load_attr, 0, sizeof(struct bpf_load_program_attr));
load_attr.prog_type = prog->type;
load_attr.expected_attach_type = prog->expected_attach_type;
/* old kernels might not support specifying expected_attach_type */
if (!prog->caps->exp_attach_type && prog->sec_def &&
prog->sec_def->is_exp_attach_type_optional)
load_attr.expected_attach_type = 0;
else
load_attr.expected_attach_type = prog->expected_attach_type;
if (prog->caps->name)
load_attr.name = prog->name;
load_attr.insns = insns;
@@ -5062,6 +5118,8 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level)
return 0;
}
static const struct bpf_sec_def *find_sec_def(const char *sec_name);
static struct bpf_object *
__bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
const struct bpf_object_open_opts *opts)
@@ -5117,24 +5175,17 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
bpf_object__elf_finish(obj);
bpf_object__for_each_program(prog, obj) {
enum bpf_prog_type prog_type;
enum bpf_attach_type attach_type;
if (prog->type != BPF_PROG_TYPE_UNSPEC)
continue;
err = libbpf_prog_type_by_name(prog->section_name, &prog_type,
&attach_type);
if (err == -ESRCH)
prog->sec_def = find_sec_def(prog->section_name);
if (!prog->sec_def)
/* couldn't guess, but user might manually specify */
continue;
if (err)
goto out;
bpf_program__set_type(prog, prog_type);
bpf_program__set_expected_attach_type(prog, attach_type);
if (prog_type == BPF_PROG_TYPE_TRACING ||
prog_type == BPF_PROG_TYPE_EXT)
bpf_program__set_type(prog, prog->sec_def->prog_type);
bpf_program__set_expected_attach_type(prog,
prog->sec_def->expected_attach_type);
if (prog->sec_def->prog_type == BPF_PROG_TYPE_TRACING ||
prog->sec_def->prog_type == BPF_PROG_TYPE_EXT)
prog->attach_prog_fd = OPTS_GET(opts, attach_prog_fd, 0);
}
@@ -6223,23 +6274,32 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog,
prog->expected_attach_type = type;
}
#define BPF_PROG_SEC_IMPL(string, ptype, eatype, is_attachable, btf, atype) \
{ string, sizeof(string) - 1, ptype, eatype, is_attachable, btf, atype }
#define BPF_PROG_SEC_IMPL(string, ptype, eatype, eatype_optional, \
attachable, attach_btf) \
{ \
.sec = string, \
.len = sizeof(string) - 1, \
.prog_type = ptype, \
.expected_attach_type = eatype, \
.is_exp_attach_type_optional = eatype_optional, \
.is_attachable = attachable, \
.is_attach_btf = attach_btf, \
}
/* Programs that can NOT be attached. */
#define BPF_PROG_SEC(string, ptype) BPF_PROG_SEC_IMPL(string, ptype, 0, 0, 0, 0)
/* Programs that can be attached. */
#define BPF_APROG_SEC(string, ptype, atype) \
BPF_PROG_SEC_IMPL(string, ptype, 0, 1, 0, atype)
BPF_PROG_SEC_IMPL(string, ptype, atype, true, 1, 0)
/* Programs that must specify expected attach type at load time. */
#define BPF_EAPROG_SEC(string, ptype, eatype) \
BPF_PROG_SEC_IMPL(string, ptype, eatype, 1, 0, eatype)
BPF_PROG_SEC_IMPL(string, ptype, eatype, false, 1, 0)
/* Programs that use BTF to identify attach point */
#define BPF_PROG_BTF(string, ptype, eatype) \
BPF_PROG_SEC_IMPL(string, ptype, eatype, 0, 1, 0)
BPF_PROG_SEC_IMPL(string, ptype, eatype, false, 0, 1)
/* Programs that can be attached but attach type can't be identified by section
* name. Kept for backward compatibility.
@@ -6253,11 +6313,6 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog,
__VA_ARGS__ \
}
struct bpf_sec_def;
typedef struct bpf_link *(*attach_fn_t)(const struct bpf_sec_def *sec,
struct bpf_program *prog);
static struct bpf_link *attach_kprobe(const struct bpf_sec_def *sec,
struct bpf_program *prog);
static struct bpf_link *attach_tp(const struct bpf_sec_def *sec,
@@ -6269,17 +6324,6 @@ static struct bpf_link *attach_trace(const struct bpf_sec_def *sec,
static struct bpf_link *attach_lsm(const struct bpf_sec_def *sec,
struct bpf_program *prog);
struct bpf_sec_def {
const char *sec;
size_t len;
enum bpf_prog_type prog_type;
enum bpf_attach_type expected_attach_type;
bool is_attachable;
bool is_attach_btf;
enum bpf_attach_type attach_type;
attach_fn_t attach_fn;
};
static const struct bpf_sec_def section_defs[] = {
BPF_PROG_SEC("socket", BPF_PROG_TYPE_SOCKET_FILTER),
BPF_PROG_SEC("sk_reuseport", BPF_PROG_TYPE_SK_REUSEPORT),
@@ -6713,7 +6757,7 @@ int libbpf_attach_type_by_name(const char *name,
continue;
if (!section_defs[i].is_attachable)
return -EINVAL;
*attach_type = section_defs[i].attach_type;
*attach_type = section_defs[i].expected_attach_type;
return 0;
}
pr_debug("failed to guess attach type based on ELF section name '%s'\n", name);
@@ -7542,7 +7586,6 @@ static struct bpf_link *attach_lsm(const struct bpf_sec_def *sec,
struct bpf_link *
bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
{
const struct bpf_sec_def *sec_def;
enum bpf_attach_type attach_type;
char errmsg[STRERR_BUFSIZE];
struct bpf_link *link;
@@ -7561,11 +7604,6 @@ bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
link->detach = &bpf_link__detach_fd;
attach_type = bpf_program__get_expected_attach_type(prog);
if (!attach_type) {
sec_def = find_sec_def(bpf_program__title(prog, false));
if (sec_def)
attach_type = sec_def->attach_type;
}
link_fd = bpf_link_create(prog_fd, cgroup_fd, attach_type, NULL);
if (link_fd < 0) {
link_fd = -errno;