On Tue, Jul 19, 2022 at 12:40 PM Joe Burton <jevburton.kernel@xxxxxxxxx> wrote:
>
> From: Joe Burton <jevburton@xxxxxxxxxx>
>
> Add an extensible variant of bpf_obj_get() capable of setting the
> `file_flags` parameter.
>
> This parameter is needed to enable unprivileged access to BPF maps.
> Without a method like this, users must manually make the syscall.
>
> Signed-off-by: Joe Burton <jevburton@xxxxxxxxxx>
Reviewed-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
For context:
We've found this out while we were trying to add support for unpriv
processes to open pinned r-x maps.
Maybe this deserves a test as well? Not sure.
> ---
> tools/lib/bpf/bpf.c | 10 ++++++++++
> tools/lib/bpf/bpf.h | 9 +++++++++
> tools/lib/bpf/libbpf.map | 1 +
> 3 files changed, 20 insertions(+)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 5eb0df90eb2b..5acb0e8bd13c 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -578,12 +578,22 @@ int bpf_obj_pin(int fd, const char *pathname)
> }
>
> int bpf_obj_get(const char *pathname)
> +{
> + LIBBPF_OPTS(bpf_obj_get_opts, opts);
> + return bpf_obj_get_opts(pathname, &opts);
> +}
> +
> +int bpf_obj_get_opts(const char *pathname, const struct bpf_obj_get_opts *opts)
> {
> union bpf_attr attr;
> int fd;
>
> + if (!OPTS_VALID(opts, bpf_obj_get_opts))
> + return libbpf_err(-EINVAL);
> +
> memset(&attr, 0, sizeof(attr));
> attr.pathname = ptr_to_u64((void *)pathname);
> + attr.file_flags = OPTS_GET(opts, file_flags, 0);
>
> fd = sys_bpf_fd(BPF_OBJ_GET, &attr, sizeof(attr));
> return libbpf_err_errno(fd);
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index 88a7cc4bd76f..f31b493b5f9a 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -270,8 +270,17 @@ LIBBPF_API int bpf_map_update_batch(int fd, const void *keys, const void *values
> __u32 *count,
> const struct bpf_map_batch_opts *opts);
>
> +struct bpf_obj_get_opts {
> + size_t sz; /* size of this struct for forward/backward compatibility */
> +
> + __u32 file_flags;
> +};
> +#define bpf_obj_get_opts__last_field file_flags
> +
> LIBBPF_API int bpf_obj_pin(int fd, const char *pathname);
> LIBBPF_API int bpf_obj_get(const char *pathname);
> +LIBBPF_API int bpf_obj_get_opts(const char *pathname,
> + const struct bpf_obj_get_opts *opts);
>
> struct bpf_prog_attach_opts {
> size_t sz; /* size of this struct for forward/backward compatibility */
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 0625adb9e888..119e6e1ea7f1 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -355,6 +355,7 @@ LIBBPF_0.8.0 {
>
> LIBBPF_1.0.0 {
> global:
> + bpf_obj_get_opts;
> bpf_prog_query_opts;
> bpf_program__attach_ksyscall;
> btf__add_enum64;
> --
> 2.37.0.170.g444d1eabd0-goog
>
