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bpf: btf: Add BPF_OBJ_GET_INFO_BY_FD support to BTF fd

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This patch adds BPF_OBJ_GET_INFO_BY_FD support to BTF fd.
The original BTF data, which was used to create the BTF fd during
the earlier BPF_BTF_LOAD call, will be returned.

The userspace is expected to allocate buffer
to info.info and the buffer size is set to info.info_len before
calling BPF_OBJ_GET_INFO_BY_FD.

The original BTF data is copied to the userspace buffer (info.info).
Only upto the user's specified info.info_len will be copied.

The original BTF data size is set to info.info_len.  The userspace
needs to check if it is bigger than its allocated buffer size.
If it is, the userspace should realloc with the kernel-returned
info.info_len and call the BPF_OBJ_GET_INFO_BY_FD again.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Martin KaFai Lau 2018-04-18 15:56:02 -07:00 committed by Daniel Borkmann
parent f56a653c1f
commit 60197cfb6e
3 changed files with 23 additions and 1 deletions
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5
include/linux/btf.h
View File

@ -10,9 +10,14 @@ struct btf;
struct btf_type;
union bpf_attr;
extern const struct file_operations btf_fops;
void btf_put(struct btf *btf);
int btf_new_fd(const union bpf_attr *attr);
struct btf *btf_get_by_fd(int fd);
int btf_get_info_by_fd(const struct btf *btf,
const union bpf_attr *attr,
union bpf_attr __user *uattr);
/* Figure out the size of a type_id. If type_id is a modifier
* (e.g. const), it will be resolved to find out the type with size.
*

17
kernel/bpf/btf.c
View File

@ -2002,7 +2002,7 @@ static int btf_release(struct inode *inode, struct file *filp)
return 0;
}
static const struct file_operations btf_fops = {
const struct file_operations btf_fops = {
.release = btf_release,
};
@ -2047,3 +2047,18 @@ struct btf *btf_get_by_fd(int fd)
return btf;
}
int btf_get_info_by_fd(const struct btf *btf,
const union bpf_attr *attr,
union bpf_attr __user *uattr)
{
void __user *udata = u64_to_user_ptr(attr->info.info);
u32 copy_len = min_t(u32, btf->data_size,
attr->info.info_len);
if (copy_to_user(udata, btf->data, copy_len) ||
put_user(btf->data_size, &uattr->info.info_len))
return -EFAULT;
return 0;
}

2
kernel/bpf/syscall.c
View File

@ -2017,6 +2017,8 @@ static int bpf_obj_get_info_by_fd(const union bpf_attr *attr,
else if (f.file->f_op == &bpf_map_fops)
err = bpf_map_get_info_by_fd(f.file->private_data, attr,
uattr);
else if (f.file->f_op == &btf_fops)
err = btf_get_info_by_fd(f.file->private_data, attr, uattr);
else
err = -EINVAL;