packet04-tailgrow: add xdp_prog_kern2.c with more attempts

Still trying to find smarter ways to access data_end.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>

Author: netoptimizer

packet04-tailgrow/Makefile

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
 
-XDP_TARGETS  := xdp_prog_kern
+XDP_TARGETS  := xdp_prog_kern xdp_prog_kern2
 # USER_TARGETS :=
 
 LIBBPF_DIR = ../libbpf/src/

packet04-tailgrow/xdp_prog_kern2.c

@@ -0,0 +1,184 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/bpf.h>
+#include <linux/in.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+
+// The parsing helper functions from the packet01 lesson have moved here
+#include "../common/parsing_helpers.h"
+#include "../common/rewrite_helpers.h"
+
+/* Defines xdp_stats_map */
+#include "../common/xdp_stats_kern_user.h"
+#include "../common/xdp_stats_kern.h"
+
+#define MTU 1536
+#define MIN_LEN 64
+
+SEC("xdp_test1b")
+int _xdp_test1b(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data     = (void *)(long)ctx->data;
+	unsigned char *ptr;
+	unsigned int i;
+	void *pos;
+
+	unsigned int offset = MIN_LEN;
+
+	pos = data;
+
+	/* Verifier can handle this bounded basic-loop construct */
+	for (i = 0; i < (MTU - MIN_LEN); i++ ) {
+		if (pos + offset > data_end) {
+			/* Promise verifier no access beyond data_end */
+			goto out;
+		}
+		if (pos + offset == data_end) {
+			/* Found data_end, exit for-loop and read data.
+			 *
+			 * It seems strange, that finding data_end via
+			 * moving pos (data) pointer forward is needed.
+			 * This is because pointer arithmetic on pkt_end is
+			 * prohibited by verifer.
+			 *
+			 * In principle data_end points to byte that is not
+			 * accessible. Thus, accessing last readable byte
+			 * via (data_end - 1) is prohibited by verifer.
+			 */
+			goto read;
+		}
+		offset++;
+	}
+	/* Show verifier all other cases exit program */
+	goto out;
+
+read:
+//	ptr = pos + (offset - );
+//	ptr = pos + (offset - sizeof(*ptr) - 1);
+	ptr = pos + (offset - sizeof(*ptr));
+	if (*ptr == 0xFF)
+		return XDP_ABORTED;
+out:
+	return XDP_PASS;
+}
+
+
+SEC("xdp_test1")
+int _xdp_test1(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data     = (void *)(long)ctx->data;
+	unsigned char *ptr;
+	unsigned int i;
+	void *pos;
+
+	unsigned int offset = 64;
+
+	pos = data;
+
+	if (pos + 64 > data_end)
+		goto out;
+
+	for (i = 0; i < (1536-64); i++ ) {
+		if (pos + offset > data_end) {
+			goto out;
+		}
+		if (pos + offset == data_end) {
+			goto read;
+		}
+		offset++;
+	}
+	goto out;
+
+read:
+//	ptr = pos + (offset - );
+//	ptr = pos + (offset - sizeof(*ptr) - 1);
+	ptr = pos + (offset - sizeof(*ptr));
+	if (*ptr == 0xFF)
+		return XDP_ABORTED;
+out:
+	return XDP_PASS;
+}
+
+
+SEC("xdp_test2")
+int _xdp_test2(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	struct hdr_cursor nh;
+	unsigned char *ptr;
+
+	unsigned int offset = 64;
+
+	nh.pos = data;
+
+	if (nh.pos + offset > data_end)
+		goto out;
+
+//	ptr = nh.pos + (offset - 1);
+	ptr = nh.pos + (offset - sizeof(*ptr));
+	if (*ptr == 0xFF)
+		return XDP_ABORTED;
+out:
+	return xdp_stats_record_action(ctx, XDP_PASS);
+}
+
+/* Invalid:
+SEC("xdp_test3")
+int _xdp_test3(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	unsigned char *ptr;
+	void *pos;
+
+	unsigned int offset = data_end - data;
+
+	if (offset < 2)
+		goto out;
+
+	pos = data;
+
+	if (pos + offset > data_end)
+		goto out;
+
+	ptr = pos + (offset - sizeof(*ptr));
+	if (*ptr == 0xFF)
+		return XDP_ABORTED;
+out:
+	return XDP_PASS;
+}
+*/
+
+/* Also invalid
+SEC("xdp_test4")
+int _xdp_test4(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	volatile unsigned char *ptr;
+	volatile void *pos;
+
+	pos = data_end;
+
+#pragma clang optimize off
+	if (pos - 1 > data_end)
+		goto out;
+
+	ptr = pos - 2;  //Err: "pointer arithmetic on pkt_end prohibited"
+	if (*ptr == 0xFF)
+		return XDP_ABORTED;
+#pragma clang optimize on
+out:
+	return XDP_PASS;
+}
+*/
+
+
+SEC("xdp_pass")
+int xdp_pass_f1(struct xdp_md *ctx)
+{
+	return xdp_stats_record_action(ctx, XDP_PASS);
+}
+