On Mon, Nov 9, 2020 at 1:55 PM Martin KaFai Lau <kafai@xxxxxx> wrote:
>
> On Mon, Nov 09, 2020 at 01:00:21PM -0800, Andrii Nakryiko wrote:
> > Allocate ID for vmlinux BTF. This makes it visible when iterating over all BTF
> > objects in the system. To allow distinguishing vmlinux BTF (and later kernel
> > module BTF) from user-provided BTFs, expose extra kernel_btf flag, as well as
> > BTF name ("vmlinux" for vmlinux BTF, will equal to module's name for module
> > BTF). We might want to later allow specifying BTF name for user-provided BTFs
> > as well, if that makes sense. But currently this is reserved only for
> > in-kernel BTFs.
> >
> > Having in-kernel BTFs exposed IDs will allow to extend BPF APIs that require
> > in-kernel BTF type with ability to specify BTF types from kernel modules, not
> > just vmlinux BTF. This will be implemented in a follow up patch set for
> > fentry/fexit/fmod_ret/lsm/etc.
> >
> > Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > ---
> > include/uapi/linux/bpf.h | 3 +++
> > kernel/bpf/btf.c | 39 ++++++++++++++++++++++++++++++++--
> > tools/include/uapi/linux/bpf.h | 3 +++
> > 3 files changed, 43 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 9879d6793e90..162999b12790 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -4466,6 +4466,9 @@ struct bpf_btf_info {
> > __aligned_u64 btf;
> > __u32 btf_size;
> > __u32 id;
> > + __aligned_u64 name;
> > + __u32 name_len;
> > + __u32 kernel_btf;
> > } __attribute__((aligned(8)));
> >
> > struct bpf_link_info {
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index 894ee33f4c84..663c3fb4e614 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -215,6 +215,8 @@ struct btf {
> > struct btf *base_btf;
> > u32 start_id; /* first type ID in this BTF (0 for base BTF) */
> > u32 start_str_off; /* first string offset (0 for base BTF) */
> > + char name[MODULE_NAME_LEN];
> > + bool kernel_btf;
> > };
> >
> > enum verifier_phase {
> > @@ -4430,6 +4432,8 @@ struct btf *btf_parse_vmlinux(void)
> >
> > btf->data = __start_BTF;
> > btf->data_size = __stop_BTF - __start_BTF;
> > + btf->kernel_btf = true;
> > + snprintf(btf->name, sizeof(btf->name), "vmlinux");
> >
> > err = btf_parse_hdr(env);
> > if (err)
> > @@ -4455,8 +4459,13 @@ struct btf *btf_parse_vmlinux(void)
> >
> > bpf_struct_ops_init(btf, log);
> >
> > - btf_verifier_env_free(env);
> > refcount_set(&btf->refcnt, 1);
> > +
> > + err = btf_alloc_id(btf);
> > + if (err)
> > + goto errout;
> > +
> > + btf_verifier_env_free(env);
> > return btf;
> >
> > errout:
> > @@ -5554,7 +5563,8 @@ int btf_get_info_by_fd(const struct btf *btf,
> > struct bpf_btf_info info;
> > u32 info_copy, btf_copy;
> > void __user *ubtf;
> > - u32 uinfo_len;
> > + char __user *uname;
> > + u32 uinfo_len, uname_len, name_len;
> >
> > uinfo = u64_to_user_ptr(attr->info.info);
> > uinfo_len = attr->info.info_len;
> > @@ -5571,6 +5581,31 @@ int btf_get_info_by_fd(const struct btf *btf,
> > return -EFAULT;
> > info.btf_size = btf->data_size;
> >
> > + info.kernel_btf = btf->kernel_btf;
> > +
> > + uname = u64_to_user_ptr(info.name);
> > + uname_len = info.name_len;
> > + if (!uname ^ !uname_len)
> > + return -EINVAL;
> > +
> > + name_len = strlen(btf->name);
> > + info.name_len = name_len;
> > +
> > + if (uname) {
> > + if (uname_len >= name_len + 1) {
> > + if (copy_to_user(uname, btf->name, name_len + 1))
> > + return -EFAULT;
> > + } else {
> > + char zero = '\0';
> > +
> > + if (copy_to_user(uname, btf->name, uname_len - 1))
> > + return -EFAULT;
> > + if (put_user(zero, uname + uname_len - 1))
> > + return -EFAULT;
> > + return -ENOSPC;
> It should still do copy_to_user() even it will return -ENOSPC.
>
Good catch! I'll use "ret" variable, will set it to -ENOSPC here and
will let the code fall through.
> > + }
> > + }
> > +
> > if (copy_to_user(uinfo, &info, info_copy) ||
> > put_user(info_copy, &uattr->info.info_len))
> > return -EFAULT;
