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libbpf: Support attachment of BPF tracing programs to kernel modules
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Teach libbpf to search for BTF types in kernel modules for tracing BPF
programs. This allows attachment of raw_tp/fentry/fexit/fmod_ret/etc BPF
program types to tracepoints and functions in kernel modules.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201203204634.1325171-13-andrii@kernel.org
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Andrii Nakryiko authored and Alexei Starovoitov committed Dec 4, 2020
1 parent 6aef10a commit 91abb4a
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Showing 3 changed files with 112 additions and 32 deletions.
5 changes: 4 additions & 1 deletion tools/lib/bpf/bpf.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -231,8 +231,11 @@ int libbpf__bpf_prog_load(const struct bpf_prog_load_params *load_attr)
attr.prog_type = load_attr->prog_type;
attr.expected_attach_type = load_attr->expected_attach_type;

if (load_attr->attach_prog_fd)
attr.attach_prog_fd = load_attr->attach_prog_fd;
else
attr.attach_btf_obj_fd = load_attr->attach_btf_obj_fd;
attr.attach_btf_id = load_attr->attach_btf_id;
attr.attach_prog_fd = load_attr->attach_prog_fd;

attr.prog_ifindex = load_attr->prog_ifindex;
attr.kern_version = load_attr->kern_version;
Expand Down
138 changes: 107 additions & 31 deletions tools/lib/bpf/libbpf.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -278,6 +278,7 @@ struct bpf_program {
enum bpf_prog_type type;
enum bpf_attach_type expected_attach_type;
int prog_ifindex;
__u32 attach_btf_obj_fd;
__u32 attach_btf_id;
__u32 attach_prog_fd;
void *func_info;
Expand Down Expand Up @@ -408,6 +409,7 @@ struct module_btf {
struct btf *btf;
char *name;
__u32 id;
int fd;
};

struct bpf_object {
Expand Down Expand Up @@ -4766,8 +4768,7 @@ static int load_module_btfs(struct bpf_object *obj)
if (err) {
err = -errno;
pr_warn("failed to get BTF object #%d info: %d\n", id, err);
close(fd);
return err;
goto err_out;
}

/* ignore non-module BTFs */
Expand All @@ -4777,25 +4778,33 @@ static int load_module_btfs(struct bpf_object *obj)
}

btf = btf_get_from_fd(fd, obj->btf_vmlinux);
close(fd);
if (IS_ERR(btf)) {
pr_warn("failed to load module [%s]'s BTF object #%d: %ld\n",
name, id, PTR_ERR(btf));
return PTR_ERR(btf);
err = PTR_ERR(btf);
goto err_out;
}

err = btf_ensure_mem((void **)&obj->btf_modules, &obj->btf_module_cap,
sizeof(*obj->btf_modules), obj->btf_module_cnt + 1);
if (err)
return err;
goto err_out;

mod_btf = &obj->btf_modules[obj->btf_module_cnt++];

mod_btf->btf = btf;
mod_btf->id = id;
mod_btf->fd = fd;
mod_btf->name = strdup(name);
if (!mod_btf->name)
return -ENOMEM;
if (!mod_btf->name) {
err = -ENOMEM;
goto err_out;
}
continue;

err_out:
close(fd);
return err;
}

return 0;
Expand Down Expand Up @@ -6841,7 +6850,10 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
load_attr.insn_cnt = insns_cnt;
load_attr.license = license;
load_attr.attach_btf_id = prog->attach_btf_id;
load_attr.attach_prog_fd = prog->attach_prog_fd;
if (prog->attach_prog_fd)
load_attr.attach_prog_fd = prog->attach_prog_fd;
else
load_attr.attach_btf_obj_fd = prog->attach_btf_obj_fd;
load_attr.attach_btf_id = prog->attach_btf_id;
load_attr.kern_version = kern_version;
load_attr.prog_ifindex = prog->prog_ifindex;
Expand Down Expand Up @@ -6937,11 +6949,11 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
return ret;
}

static int libbpf_find_attach_btf_id(struct bpf_program *prog);
static int libbpf_find_attach_btf_id(struct bpf_program *prog, int *btf_obj_fd, int *btf_type_id);

int bpf_program__load(struct bpf_program *prog, char *license, __u32 kern_ver)
{
int err = 0, fd, i, btf_id;
int err = 0, fd, i;

if (prog->obj->loaded) {
pr_warn("prog '%s': can't load after object was loaded\n", prog->name);
Expand All @@ -6951,10 +6963,14 @@ int bpf_program__load(struct bpf_program *prog, char *license, __u32 kern_ver)
if ((prog->type == BPF_PROG_TYPE_TRACING ||
prog->type == BPF_PROG_TYPE_LSM ||
prog->type == BPF_PROG_TYPE_EXT) && !prog->attach_btf_id) {
btf_id = libbpf_find_attach_btf_id(prog);
if (btf_id <= 0)
return btf_id;
prog->attach_btf_id = btf_id;
int btf_obj_fd = 0, btf_type_id = 0;

err = libbpf_find_attach_btf_id(prog, &btf_obj_fd, &btf_type_id);
if (err)
return err;

prog->attach_btf_obj_fd = btf_obj_fd;
prog->attach_btf_id = btf_type_id;
}

if (prog->instances.nr < 0 || !prog->instances.fds) {
Expand Down Expand Up @@ -7467,6 +7483,7 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)

/* clean up module BTFs */
for (i = 0; i < obj->btf_module_cnt; i++) {
close(obj->btf_modules[i].fd);
btf__free(obj->btf_modules[i].btf);
free(obj->btf_modules[i].name);
}
Expand Down Expand Up @@ -8821,8 +8838,8 @@ static int find_btf_by_prefix_kind(const struct btf *btf, const char *prefix,
return btf__find_by_name_kind(btf, btf_type_name, kind);
}

static inline int __find_vmlinux_btf_id(struct btf *btf, const char *name,
enum bpf_attach_type attach_type)
static inline int find_attach_btf_id(struct btf *btf, const char *name,
enum bpf_attach_type attach_type)
{
int err;

Expand All @@ -8838,9 +8855,6 @@ static inline int __find_vmlinux_btf_id(struct btf *btf, const char *name,
else
err = btf__find_by_name_kind(btf, name, BTF_KIND_FUNC);

if (err <= 0)
pr_warn("%s is not found in vmlinux BTF\n", name);

return err;
}

Expand All @@ -8856,7 +8870,10 @@ int libbpf_find_vmlinux_btf_id(const char *name,
return -EINVAL;
}

err = __find_vmlinux_btf_id(btf, name, attach_type);
err = find_attach_btf_id(btf, name, attach_type);
if (err <= 0)
pr_warn("%s is not found in vmlinux BTF\n", name);

btf__free(btf);
return err;
}
Expand Down Expand Up @@ -8894,11 +8911,49 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
return err;
}

static int libbpf_find_attach_btf_id(struct bpf_program *prog)
static int find_kernel_btf_id(struct bpf_object *obj, const char *attach_name,
enum bpf_attach_type attach_type,
int *btf_obj_fd, int *btf_type_id)
{
int ret, i;

ret = find_attach_btf_id(obj->btf_vmlinux, attach_name, attach_type);
if (ret > 0) {
*btf_obj_fd = 0; /* vmlinux BTF */
*btf_type_id = ret;
return 0;
}
if (ret != -ENOENT)
return ret;

ret = load_module_btfs(obj);
if (ret)
return ret;

for (i = 0; i < obj->btf_module_cnt; i++) {
const struct module_btf *mod = &obj->btf_modules[i];

ret = find_attach_btf_id(mod->btf, attach_name, attach_type);
if (ret > 0) {
*btf_obj_fd = mod->fd;
*btf_type_id = ret;
return 0;
}
if (ret == -ENOENT)
continue;

return ret;
}

return -ESRCH;
}

static int libbpf_find_attach_btf_id(struct bpf_program *prog, int *btf_obj_fd, int *btf_type_id)
{
enum bpf_attach_type attach_type = prog->expected_attach_type;
__u32 attach_prog_fd = prog->attach_prog_fd;
const char *name = prog->sec_name;
const char *name = prog->sec_name, *attach_name;
const struct bpf_sec_def *sec = NULL;
int i, err;

if (!name)
Expand All @@ -8909,17 +8964,37 @@ static int libbpf_find_attach_btf_id(struct bpf_program *prog)
continue;
if (strncmp(name, section_defs[i].sec, section_defs[i].len))
continue;
if (attach_prog_fd)
err = libbpf_find_prog_btf_id(name + section_defs[i].len,
attach_prog_fd);
else
err = __find_vmlinux_btf_id(prog->obj->btf_vmlinux,
name + section_defs[i].len,
attach_type);

sec = &section_defs[i];
break;
}

if (!sec) {
pr_warn("failed to identify BTF ID based on ELF section name '%s'\n", name);
return -ESRCH;
}
attach_name = name + sec->len;

/* BPF program's BTF ID */
if (attach_prog_fd) {
err = libbpf_find_prog_btf_id(attach_name, attach_prog_fd);
if (err < 0) {
pr_warn("failed to find BPF program (FD %d) BTF ID for '%s': %d\n",
attach_prog_fd, attach_name, err);
return err;
}
*btf_obj_fd = 0;
*btf_type_id = err;
return 0;
}

/* kernel/module BTF ID */
err = find_kernel_btf_id(prog->obj, attach_name, attach_type, btf_obj_fd, btf_type_id);
if (err) {
pr_warn("failed to find kernel BTF type ID of '%s': %d\n", attach_name, err);
return err;
}
pr_warn("failed to identify btf_id based on ELF section name '%s'\n", name);
return -ESRCH;
return 0;
}

int libbpf_attach_type_by_name(const char *name,
Expand Down Expand Up @@ -10808,6 +10883,7 @@ int bpf_program__set_attach_target(struct bpf_program *prog,
return btf_id;

prog->attach_btf_id = btf_id;
prog->attach_btf_obj_fd = 0;
prog->attach_prog_fd = attach_prog_fd;
return 0;
}
Expand Down
1 change: 1 addition & 0 deletions tools/lib/bpf/libbpf_internal.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -160,6 +160,7 @@ struct bpf_prog_load_params {
const char *license;
__u32 kern_version;
__u32 attach_prog_fd;
__u32 attach_btf_obj_fd;
__u32 attach_btf_id;
__u32 prog_ifindex;
__u32 prog_btf_fd;
Expand Down

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