Re: [RFC PATCH bpf-next 4/5] bpf: load and verify kernel module BTFs

[Jakub Kicinski]

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),