selftests: drv-net: Test head-adjustment support

Add test to validate the headroom adjustment support for both extension
and the shrinking cases. For the extension part, eat up space from
the start of payload data whereas, for the shrinking part, populate
the newly available space with a tag. In the user-space, validate that a
test string is manipulated accordingly.
The negative and positive offset values result in shrinking and growing of
headroom (growing and shrinking of payload) respectively.

TAP version 13
1..9
ok 1 xdp.test_xdp_native_pass_sb
ok 2 xdp.test_xdp_native_pass_mb
ok 3 xdp.test_xdp_native_drop_sb
ok 4 xdp.test_xdp_native_drop_mb
ok 5 xdp.test_xdp_native_tx_mb
\# Failed run: pkt_sz 512, ... offset 1. Reason: Adjustment failed
ok 6 xdp.test_xdp_native_adjst_tail_grow_data
ok 7 xdp.test_xdp_native_adjst_tail_shrnk_data
\# Failed run: pkt_sz 512, ... offset -128. Reason: Adjustment failed
ok 8 xdp.test_xdp_native_adjst_head_grow_data
\# Failed run: pkt_sz (512) > HDS threshold (0) and offset 64 > 48
ok 9 xdp.test_xdp_native_adjst_head_shrnk_data
\# Totals: pass:9 fail:0 xfail:0 xpass:0 skip:0 error:0

Signed-off-by: Mohsin Bashir <mohsin.bashr@gmail.com>
Link: https://patch.msgid.link/20250719083059.3209169-6-mohsin.bashr@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 181 insertions, 0 deletions

diff --git a/tools/testing/selftests/net/lib/xdp_native.bpf.c b/tools/testing/selftests/net/lib/xdp_native.bpf.c
index 7bb2dff86d8f..521ba38f2ddd 100644
--- a/tools/testing/selftests/net/lib/xdp_native.bpf.c
+++ b/tools/testing/selftests/net/lib/xdp_native.bpf.c
@@ -26,6 +26,7 @@ enum {
 	XDP_MODE_DROP = 1,
 	XDP_MODE_TX = 2,
 	XDP_MODE_TAIL_ADJST = 3,
+	XDP_MODE_HEAD_ADJST = 4,
 } xdp_map_modes;
 
 enum {
@@ -395,6 +396,184 @@ abort_pkt:
 	return XDP_ABORTED;
 }
 
+static int xdp_adjst_head_shrnk_data(struct xdp_md *ctx, __u64 hdr_len,
+				     __u32 offset)
+{
+	char tmp_buff[MAX_ADJST_OFFSET];
+	struct udphdr *udph;
+	void *offset_ptr;
+	__u32 udp_csum = 0;
+
+	/* Update the length information in the IP and UDP headers before
+	 * adjusting the headroom. This simplifies accessing the relevant
+	 * fields in the IP and UDP headers for fragmented packets. Any
+	 * failure beyond this point will result in the packet being aborted,
+	 * so we don't need to worry about incorrect length information for
+	 * passed packets.
+	 */
+	udph = update_pkt(ctx, (__s16)(0 - offset), &udp_csum);
+	if (!udph)
+		return -1;
+
+	offset = (offset & 0x1ff) >= MAX_ADJST_OFFSET ? MAX_ADJST_OFFSET :
+				     offset & 0xff;
+	if (offset == 0)
+		return -1;
+
+	if (bpf_xdp_load_bytes(ctx, hdr_len, tmp_buff, offset) < 0)
+		return -1;
+
+	udp_csum = bpf_csum_diff((__be32 *)tmp_buff, offset, 0, 0, udp_csum);
+
+	udph->check = (__u16)csum_fold_helper(udp_csum);
+
+	if (bpf_xdp_load_bytes(ctx, 0, tmp_buff, MAX_ADJST_OFFSET) < 0)
+		return -1;
+
+	if (bpf_xdp_adjust_head(ctx, offset) < 0)
+		return -1;
+
+	if (offset > MAX_ADJST_OFFSET)
+		return -1;
+
+	if (hdr_len > MAX_ADJST_OFFSET || hdr_len == 0)
+		return -1;
+
+	/* Added here to handle clang complain about negative value */
+	hdr_len = hdr_len & 0xff;
+
+	if (hdr_len == 0)
+		return -1;
+
+	if (bpf_xdp_store_bytes(ctx, 0, tmp_buff, hdr_len) < 0)
+		return -1;
+
+	return 0;
+}
+
+static int xdp_adjst_head_grow_data(struct xdp_md *ctx, __u64 hdr_len,
+				    __u32 offset)
+{
+	char hdr_buff[MAX_HDR_LEN];
+	char data_buff[MAX_ADJST_OFFSET];
+	void *offset_ptr;
+	__s32 *val;
+	__u32 key;
+	__u8 tag;
+	__u32 udp_csum = 0;
+	struct udphdr *udph;
+
+	udph = update_pkt(ctx, (__s16)(offset), &udp_csum);
+	if (!udph)
+		return -1;
+
+	key = XDP_ADJST_TAG;
+	val = bpf_map_lookup_elem(&map_xdp_setup, &key);
+	if (!val)
+		return -1;
+
+	tag = (__u8)(*val);
+	for (int i = 0; i < MAX_ADJST_OFFSET; i++)
+		__builtin_memcpy(&data_buff[i], &tag, 1);
+
+	offset = (offset & 0x1ff) >= MAX_ADJST_OFFSET ? MAX_ADJST_OFFSET :
+				     offset & 0xff;
+	if (offset == 0)
+		return -1;
+
+	udp_csum = bpf_csum_diff(0, 0, (__be32 *)data_buff, offset, udp_csum);
+	udph->check = (__u16)csum_fold_helper(udp_csum);
+
+	if (hdr_len > MAX_ADJST_OFFSET || hdr_len == 0)
+		return -1;
+
+	/* Added here to handle clang complain about negative value */
+	hdr_len = hdr_len & 0xff;
+
+	if (hdr_len == 0)
+		return -1;
+
+	if (bpf_xdp_load_bytes(ctx, 0, hdr_buff, hdr_len) < 0)
+		return -1;
+
+	if (offset > MAX_ADJST_OFFSET)
+		return -1;
+
+	if (bpf_xdp_adjust_head(ctx, 0 - offset) < 0)
+		return -1;
+
+	if (bpf_xdp_store_bytes(ctx, 0, hdr_buff, hdr_len) < 0)
+		return -1;
+
+	if (bpf_xdp_store_bytes(ctx, hdr_len, data_buff, offset) < 0)
+		return -1;
+
+	return 0;
+}
+
+static int xdp_head_adjst(struct xdp_md *ctx, __u16 port)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	struct udphdr *udph_ptr = NULL;
+	__u32 key, size, hdr_len;
+	__s32 *val;
+	int res;
+
+	/* Filter packets based on UDP port */
+	udph_ptr = filter_udphdr(ctx, port);
+	if (!udph_ptr)
+		return XDP_PASS;
+
+	hdr_len = (void *)udph_ptr - data + sizeof(struct udphdr);
+
+	key = XDP_ADJST_OFFSET;
+	val = bpf_map_lookup_elem(&map_xdp_setup, &key);
+	if (!val)
+		return XDP_PASS;
+
+	switch (*val) {
+	case -16:
+	case 16:
+		size = 16;
+		break;
+	case -32:
+	case 32:
+		size = 32;
+		break;
+	case -64:
+	case 64:
+		size = 64;
+		break;
+	case -128:
+	case 128:
+		size = 128;
+		break;
+	case -256:
+	case 256:
+		size = 256;
+		break;
+	default:
+		bpf_printk("Invalid adjustment offset: %d\n", *val);
+		goto abort;
+	}
+
+	if (*val < 0)
+		res = xdp_adjst_head_grow_data(ctx, hdr_len, size);
+	else
+		res = xdp_adjst_head_shrnk_data(ctx, hdr_len, size);
+
+	if (res)
+		goto abort;
+
+	record_stats(ctx, STATS_PASS);
+	return XDP_PASS;
+
+abort:
+	record_stats(ctx, STATS_ABORT);
+	return XDP_ABORTED;
+}
+
 static int xdp_prog_common(struct xdp_md *ctx)
 {
 	__u32 key, *port;
@@ -419,6 +598,8 @@ static int xdp_prog_common(struct xdp_md *ctx)
 		return xdp_mode_tx_handler(ctx, (__u16)(*port));
 	case XDP_MODE_TAIL_ADJST:
 		return xdp_adjst_tail(ctx, (__u16)(*port));
+	case XDP_MODE_HEAD_ADJST:
+		return xdp_head_adjst(ctx, (__u16)(*port));
 	}
 
 	/* Default action is to simple pass */