Re: [PATCH bpf] xdp: use trusted arguments in XDP hints kfuncs

[Jesper Dangaard Brouer]

On 11/07/2023 12.59, Larysa Zaremba wrote:
> Currently, verifier does not reject XDP programs that pass NULL pointer to
> hints functions. At the same time, this case is not handled in any driver
> implementation (including veth). For example, changing
>
> bpf_xdp_metadata_rx_timestamp(ctx, &timestamp);
>
> to
>
> bpf_xdp_metadata_rx_timestamp(ctx, NULL);
>
> in xdp_metadata test successfully crashes the system.
>
> Add KF_TRUSTED_ARGS flag to hints kfunc definitions, so driver code
> does not have to worry about getting invalid pointers.

Looks good to me, assuming this means verifier will reject BPF-prog's 
supplying NULL.

Acked-by: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>

> Fixes: 3d76a4d3d4e5 ("bpf: XDP metadata RX kfuncs")
> Reported-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> Closes: https://lore.kernel.org/bpf/ZKWo0BbpLfkZHbyE@xxxxxxxxxx/
> Signed-off-by: Larysa Zaremba <larysa.zaremba@xxxxxxxxx>
> ---
>   net/core/xdp.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 41e5ca8643ec..8362130bf085 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -741,7 +741,7 @@ __bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash,
>   __diag_pop();
>   
>   BTF_SET8_START(xdp_metadata_kfunc_ids)
> -#define XDP_METADATA_KFUNC(_, name) BTF_ID_FLAGS(func, name, 0)
> +#define XDP_METADATA_KFUNC(_, name) BTF_ID_FLAGS(func, name, KF_TRUSTED_ARGS)
>   XDP_METADATA_KFUNC_xxx
>   #undef XDP_METADATA_KFUNC
>   BTF_SET8_END(xdp_metadata_kfunc_ids)