On Wed, 4 Nov 2020 20:51:39 -0800 Andrii Nakryiko wrote:
> Add kernel module listener that will load/validate and unload module BTF.
> Module BTFs gets ID generated for them, which makes it possible to iterate
> them with existing BTF iteration API. They are given their respective module's
> names, which will get reported through GET_OBJ_INFO API. They are also marked
> as in-kernel BTFs for tooling to distinguish them from user-provided BTFs.
>
> Also, similarly to vmlinux BTF, kernel module BTFs are exposed through
> sysfs as /sys/kernel/btf/<module-name>. This is convenient for user-space
> tools to inspect module BTF contents and dump their types with existing tools:
Is there any precedent for creating per-module files under a new
sysfs directory structure? My intuition would be that these files
belong under /sys/module/
Also the CC list on these patches is quite narrow. You should have
at least CCed the module maintainer. Adding some folks now.
> [vmuser@archvm bpf]$ ls -la /sys/kernel/btf
> total 0
> drwxr-xr-x 2 root root 0 Nov 4 19:46 .
> drwxr-xr-x 13 root root 0 Nov 4 19:46 ..
>
> ...
>
> -r--r--r-- 1 root root 888 Nov 4 19:46 irqbypass
> -r--r--r-- 1 root root 100225 Nov 4 19:46 kvm
> -r--r--r-- 1 root root 35401 Nov 4 19:46 kvm_intel
> -r--r--r-- 1 root root 120 Nov 4 19:46 pcspkr
> -r--r--r-- 1 root root 399 Nov 4 19:46 serio_raw
> -r--r--r-- 1 root root 4094095 Nov 4 19:46 vmlinux
>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> ---
> include/linux/bpf.h | 2 +
> include/linux/module.h | 4 +
> kernel/bpf/btf.c | 193 +++++++++++++++++++++++++++++++++++++++++
> kernel/bpf/sysfs_btf.c | 2 +-
> kernel/module.c | 32 +++++++
> 5 files changed, 232 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 2fffd30e13ac..3cb89cd7177b 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -36,9 +36,11 @@ struct seq_operations;
> struct bpf_iter_aux_info;
> struct bpf_local_storage;
> struct bpf_local_storage_map;
> +struct kobject;
>
> extern struct idr btf_idr;
> extern spinlock_t btf_idr_lock;
> +extern struct kobject *btf_kobj;
>
> typedef int (*bpf_iter_init_seq_priv_t)(void *private_data,
> struct bpf_iter_aux_info *aux);
> diff --git a/include/linux/module.h b/include/linux/module.h
> index a29187f7c360..20fce258ffba 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -475,6 +475,10 @@ struct module {
> unsigned int num_bpf_raw_events;
> struct bpf_raw_event_map *bpf_raw_events;
> #endif
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> + unsigned int btf_data_size;
> + void *btf_data;
> +#endif
> #ifdef CONFIG_JUMP_LABEL
> struct jump_entry *jump_entries;
> unsigned int num_jump_entries;
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 6a99677e57c0..475d1b95b3d8 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -23,6 +23,8 @@
> #include <linux/perf_event.h>
> #include <linux/bsearch.h>
> #include <linux/btf_ids.h>
> +#include <linux/kobject.h>
> +#include <linux/sysfs.h>
> #include <net/sock.h>
>
> /* BTF (BPF Type Format) is the meta data format which describes
> @@ -4487,6 +4489,75 @@ struct btf *btf_parse_vmlinux(void)
> return ERR_PTR(err);
> }
>
> +static struct btf *btf_parse_module(const char *module_name, const void *data, unsigned int data_size)
> +{
> + struct btf_verifier_env *env = NULL;
> + struct bpf_verifier_log *log;
> + struct btf *btf = NULL, *base_btf;
> + int err;
> +
> + base_btf = bpf_get_btf_vmlinux();
> + if (IS_ERR(base_btf))
> + return base_btf;
> + if (!base_btf)
> + return ERR_PTR(-EINVAL);
> +
> + env = kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN);
> + if (!env)
> + return ERR_PTR(-ENOMEM);
> +
> + log = &env->log;
> + log->level = BPF_LOG_KERNEL;
> +
> + btf = kzalloc(sizeof(*btf), GFP_KERNEL | __GFP_NOWARN);
> + if (!btf) {
> + err = -ENOMEM;
> + goto errout;
> + }
> + env->btf = btf;
> +
> + btf->base_btf = base_btf;
> + btf->start_id = base_btf->nr_types;
> + btf->start_str_off = base_btf->hdr.str_len;
> + btf->kernel_btf = true;
> + snprintf(btf->name, sizeof(btf->name), "%s", module_name);
> +
> + btf->data = kvmalloc(data_size, GFP_KERNEL | __GFP_NOWARN);
> + if (!btf->data) {
> + err = -ENOMEM;
> + goto errout;
> + }
> + memcpy(btf->data, data, data_size);
> + btf->data_size = data_size;
> +
> + err = btf_parse_hdr(env);
> + if (err)
> + goto errout;
> +
> + btf->nohdr_data = btf->data + btf->hdr.hdr_len;
> +
> + err = btf_parse_str_sec(env);
> + if (err)
> + goto errout;
> +
> + err = btf_check_all_metas(env);
> + if (err)
> + goto errout;
> +
> + btf_verifier_env_free(env);
> + refcount_set(&btf->refcnt, 1);
> + return btf;
> +
> +errout:
> + btf_verifier_env_free(env);
> + if (btf) {
> + kvfree(btf->data);
> + kvfree(btf->types);
> + kfree(btf);
> + }
> + return ERR_PTR(err);
> +}
> +
> struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog)
> {
> struct bpf_prog *tgt_prog = prog->aux->dst_prog;
> @@ -5660,3 +5731,125 @@ bool btf_id_set_contains(const struct btf_id_set *set, u32 id)
> {
> return bsearch(&id, set->ids, set->cnt, sizeof(u32), btf_id_cmp_func) != NULL;
> }
> +
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +struct btf_module {
> + struct list_head list;
> + struct module *module;
> + struct btf *btf;
> + struct bin_attribute *sysfs_attr;
> +};
> +
> +static LIST_HEAD(btf_modules);
> +static DEFINE_MUTEX(btf_module_mutex);
> +
> +static ssize_t
> +btf_module_read(struct file *file, struct kobject *kobj,
> + struct bin_attribute *bin_attr,
> + char *buf, loff_t off, size_t len)
> +{
> + const struct btf *btf = bin_attr->private;
> +
> + memcpy(buf, btf->data + off, len);
> + return len;
> +}
> +
> +static int btf_module_notify(struct notifier_block *nb, unsigned long op,
> + void *module)
> +{
> + struct btf_module *btf_mod, *tmp;
> + struct module *mod = module;
> + struct btf *btf;
> + int err = 0;
> +
> + if (mod->btf_data_size == 0 ||
> + (op != MODULE_STATE_COMING && op != MODULE_STATE_GOING))
> + goto out;
> +
> + switch (op) {
> + case MODULE_STATE_COMING:
> + btf_mod = kzalloc(sizeof(*btf_mod), GFP_KERNEL);
> + if (!btf_mod) {
> + err = -ENOMEM;
> + goto out;
> + }
> + btf = btf_parse_module(mod->name, mod->btf_data, mod->btf_data_size);
> + if (IS_ERR(btf)) {
> + kfree(btf_mod);
> + err = PTR_ERR(btf);
> + goto out;
> + }
> + err = btf_alloc_id(btf);
> + if (err) {
> + btf_free(btf);
> + kfree(btf_mod);
> + goto out;
> + }
> +
> + mutex_lock(&btf_module_mutex);
> + btf_mod->module = module;
> + btf_mod->btf = btf;
> + list_add(&btf_mod->list, &btf_modules);
> + mutex_unlock(&btf_module_mutex);
> +
> + if (IS_ENABLED(CONFIG_SYSFS)) {
> + struct bin_attribute *attr;
> +
> + attr = kzalloc(sizeof(*attr), GFP_KERNEL);
> + if (!attr) {
> + WARN(1, "failed to register module [%s] BTF in sysfs\n", mod->name);
> + goto out;
> + }
> +
> + attr->attr.name = btf->name;
> + attr->attr.mode = 0444;
> + attr->size = btf->data_size;
> + attr->private = btf;
> + attr->read = btf_module_read;
> +
> + err = sysfs_create_bin_file(btf_kobj, attr);
> + if (err) {
> + kfree(attr);
> + WARN(1, "failed to register module [%s] BTF in sysfs: %d\n",
> + mod->name, err);
> + err = 0;
> + goto out;
> + }
> +
> + btf_mod->sysfs_attr = attr;
> + }
> +
> + break;
> + case MODULE_STATE_GOING:
> + mutex_lock(&btf_module_mutex);
> + list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
> + if (btf_mod->module != module)
> + continue;
> +
> + list_del(&btf_mod->list);
> + if (btf_mod->sysfs_attr)
> + sysfs_remove_bin_file(btf_kobj, btf_mod->sysfs_attr);
> + btf_put(btf_mod->btf);
> + kfree(btf_mod->sysfs_attr);
> + kfree(btf_mod);
> + break;
> + }
> + mutex_unlock(&btf_module_mutex);
> + break;
> + }
> +out:
> + return notifier_from_errno(err);
> +}
> +
> +static struct notifier_block btf_module_nb = {
> + .notifier_call = btf_module_notify,
> +};
> +
> +static int __init btf_module_init(void)
> +{
> + register_module_notifier(&btf_module_nb);
> + return 0;
> +}
> +
> +fs_initcall(btf_module_init);
> +#endif /* CONFIG_DEBUG_INFO_BTF_MODULES */
> diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> index 11b3380887fa..ef6911aee3bb 100644
> --- a/kernel/bpf/sysfs_btf.c
> +++ b/kernel/bpf/sysfs_btf.c
> @@ -26,7 +26,7 @@ static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
> .read = btf_vmlinux_read,
> };
>
> -static struct kobject *btf_kobj;
> +struct kobject *btf_kobj;
>
> static int __init btf_vmlinux_init(void)
> {
> diff --git a/kernel/module.c b/kernel/module.c
> index a4fa44a652a7..af71fc53eb25 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -380,6 +380,35 @@ static void *section_objs(const struct load_info *info,
> return (void *)info->sechdrs[sec].sh_addr;
> }
>
> +/* Find a module section: 0 means not found. Ignores SHF_ALLOC flag. */
> +static unsigned int find_any_sec(const struct load_info *info, const char *name)
> +{
> + unsigned int i;
> +
> + for (i = 1; i < info->hdr->e_shnum; i++) {
> + Elf_Shdr *shdr = &info->sechdrs[i];
> + if (strcmp(info->secstrings + shdr->sh_name, name) == 0)
> + return i;
> + }
> + return 0;
> +}
> +
> +/*
> + * Find a module section, or NULL. Fill in number of "objects" in section.
> + * Ignores SHF_ALLOC flag.
> + */
> +static void *any_section_objs(const struct load_info *info,
> + const char *name,
> + size_t object_size,
> + unsigned int *num)
> +{
> + unsigned int sec = find_any_sec(info, name);
> +
> + /* Section 0 has sh_addr 0 and sh_size 0. */
> + *num = info->sechdrs[sec].sh_size / object_size;
> + return (void *)info->sechdrs[sec].sh_addr;
> +}
> +
> /* Provided by the linker */
> extern const struct kernel_symbol __start___ksymtab[];
> extern const struct kernel_symbol __stop___ksymtab[];
> @@ -3250,6 +3279,9 @@ static int find_module_sections(struct module *mod, struct load_info *info)
> sizeof(*mod->bpf_raw_events),
> &mod->num_bpf_raw_events);
> #endif
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> + mod->btf_data = any_section_objs(info, ".BTF", 1, &mod->btf_data_size);
> +#endif
> #ifdef CONFIG_JUMP_LABEL
> mod->jump_entries = section_objs(info, "__jump_table",
> sizeof(*mod->jump_entries),
