bpf: Support specifying linear xdp packet data size in test_run

To test bpf_xdp_pull_data(), an xdp packet containing fragments as well
as free linear data area needs to be created. However,
bpf_prog_test_run_xdp() always fills the linear area with data_in before
creating fragments, leaving no space to pull data. This patch will allow
users to specify the linear data size through ctx->data_end.

Currently, ctx_in->data_end must match data_size_in and will not be the
final ctx->data_end seen by the xdp program. This is because
ctx->data_end is populated according to the xdp_buff passed to test_run,
which always contains PAGE_SIZE - headroom - tailroom bytes of linear
data if the linear data given by the user exceeds it.

This patch will allow user to specify the size of data that goes into
the linear area. When ctx_in->data_end is different from data_size_in,
only ctx_in->data_end bytes of data will be put into the linear area when
creating the xdp_buff.

While ctx_in->data_end will be allowed to be different from data_size_in,
it cannot be larger than the data_size_in as there will be no data to
copy from. If it is larger than the maximum linear data area size, the
layout suggested by the user will not be honored. Data beyond the
maximum linear data area size will still be put into fragments.

Signed-off-by: Amery Hung <[email protected]>

Author: ameryhung

net/bpf/test_run.c

@@ -1207,8 +1207,8 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 {
 	bool do_live = (kattr->test.flags & BPF_F_TEST_XDP_LIVE_FRAMES);
 	u32 tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+	u32 retval = 0, duration, max_data_sz, linear_data_sz;
 	u32 batch_size = kattr->test.batch_size;
-	u32 retval = 0, duration, max_data_sz;
 	u32 size = kattr->test.data_size_in;
 	u32 headroom = XDP_PACKET_HEADROOM;
 	u32 repeat = kattr->test.repeat;
@@ -1246,7 +1246,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 
 	if (ctx) {
 		/* There can't be user provided data before the meta data */
-		if (ctx->data_meta || ctx->data_end != size ||
+		if (ctx->data_meta || ctx->data_end > size ||
 		    ctx->data > ctx->data_end ||
 		    unlikely(xdp_metalen_invalid(ctx->data)) ||
 		    (do_live && (kattr->test.data_out || kattr->test.ctx_out)))
@@ -1256,11 +1256,12 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 	}
 
 	max_data_sz = PAGE_SIZE - headroom - tailroom;
-	if (size > max_data_sz) {
+	linear_data_sz = (ctx && ctx->data_end != size) ? ctx->data_end : max_data_sz;
+	if (size > linear_data_sz) {
 		/* disallow live data mode for jumbo frames */
 		if (do_live)
 			goto free_ctx;
-		size = max_data_sz;
+		size = linear_data_sz;
 	}
 
 	data = bpf_test_init(kattr, size, max_data_sz, headroom, tailroom);

tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c

@@ -96,9 +96,7 @@ void test_xdp_context_test_run(void)
 	/* Meta data must be 255 bytes or smaller */
 	test_xdp_context_error(prog_fd, opts, 0, 256, sizeof(data), 0, 0, 0);
 
-	/* Total size of data must match data_end - data_meta */
-	test_xdp_context_error(prog_fd, opts, 0, sizeof(__u32),
-			       sizeof(data) - 1, 0, 0, 0);
+	/* Total size of data must be data_end - data_meta or larger */
 	test_xdp_context_error(prog_fd, opts, 0, sizeof(__u32),
 			       sizeof(data) + 1, 0, 0, 0);