bpf: xdp: Allow head adjustment in XDP prog

This patch allows XDP prog to extend/remove the packet
data at the head (like adding or removing header).  It is
done by adding a new XDP helper bpf_xdp_adjust_head().

It also renames bpf_helper_changes_skb_data() to
bpf_helper_changes_pkt_data() to better reflect
that XDP prog does not work on skb.

This patch adds one "xdp_adjust_head" bit to bpf_prog for the
XDP-capable driver to check if the XDP prog requires
bpf_xdp_adjust_head() support.  The driver can then decide
to error out during XDP_SETUP_PROG.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 4 insertions, 2 deletions

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index bdcc9f4..83e0d15 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1143,7 +1143,7 @@ struct bpf_prog * __weak bpf_int_jit_compile(struct bpf_prog *prog)
 	return prog;
 }
 
-bool __weak bpf_helper_changes_skb_data(void *func)
+bool __weak bpf_helper_changes_pkt_data(void *func)
 {
 	return false;
 }
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 88f609f..4819ec9 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -579,6 +579,8 @@ static void fixup_bpf_calls(struct bpf_prog *prog)
 				prog->dst_needed = 1;
 			if (insn->imm == BPF_FUNC_get_prandom_u32)
 				bpf_user_rnd_init_once();
+			if (insn->imm == BPF_FUNC_xdp_adjust_head)
+				prog->xdp_adjust_head = 1;
 			if (insn->imm == BPF_FUNC_tail_call) {
 				/* mark bpf_tail_call as different opcode
 				 * to avoid conditional branch in
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5b14f85..d28f9a3 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1216,7 +1216,7 @@ static int check_call(struct bpf_verifier_env *env, int func_id)
 		return -EINVAL;
 	}
 
-	changes_data = bpf_helper_changes_skb_data(fn->func);
+	changes_data = bpf_helper_changes_pkt_data(fn->func);
 
 	memset(&meta, 0, sizeof(meta));
 	meta.pkt_access = fn->pkt_access;