[PATCH bpf-next 7/7] selftests/bpf: Add a new test based on loop6.c

[Yonghong Song <yhs@xxxxxx>]

With LLVM commit [1], loop6.c will fail verification without Commit 3c2611bac08a
("selftests/bpf: Fix trace_virtqueue_add_sgs test issue with LLVM 17.").
Also, there is an effort to fix LLVM since LLVM17 may be used by old kernels
for bpf development.

A new test is added by manually doing similar transformation in [1]
so it can be used to test related verifier changes.

  [1] https://reviews.llvm.org/D143726

Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
 .../bpf/prog_tests/bpf_verif_scale.c          |   5 +
 tools/testing/selftests/bpf/progs/loop7.c     | 102 ++++++++++++++++++
 2 files changed, 107 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/loop7.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c b/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
index 731c343897d8..cb708235e654 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_verif_scale.c
@@ -180,6 +180,11 @@ void test_verif_scale_loop6()
 	scale_test("loop6.bpf.o", BPF_PROG_TYPE_KPROBE, false);
 }
 
+void test_verif_scale_loop7()
+{
+	scale_test("loop7.bpf.o", BPF_PROG_TYPE_KPROBE, false);
+}
+
 void test_verif_scale_strobemeta()
 {
 	/* partial unroll. 19k insn in a loop.
diff --git a/tools/testing/selftests/bpf/progs/loop7.c b/tools/testing/selftests/bpf/progs/loop7.c
new file mode 100644
index 000000000000..b234ed6f0038
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/loop7.c
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/ptrace.h>
+#include <stddef.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+/* typically virtio scsi has max SGs of 6 */
+#define VIRTIO_MAX_SGS	6
+
+/* Verifier will fail with SG_MAX = 128. The failure can be
+ * workarounded with a smaller SG_MAX, e.g. 10.
+ */
+#define WORKAROUND
+#ifdef WORKAROUND
+#define SG_MAX		10
+#else
+/* typically virtio blk has max SEG of 128 */
+#define SG_MAX		128
+#endif
+
+#define SG_CHAIN	0x01UL
+#define SG_END		0x02UL
+
+struct scatterlist {
+	unsigned long   page_link;
+	unsigned int    offset;
+	unsigned int    length;
+};
+
+#define sg_is_chain(sg)		((sg)->page_link & SG_CHAIN)
+#define sg_is_last(sg)		((sg)->page_link & SG_END)
+#define sg_chain_ptr(sg)	\
+	((struct scatterlist *) ((sg)->page_link & ~(SG_CHAIN | SG_END)))
+
+static inline struct scatterlist *__sg_next(struct scatterlist *sgp)
+{
+	struct scatterlist sg;
+
+	bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
+	if (sg_is_last(&sg))
+		return NULL;
+
+	sgp++;
+
+	bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
+	if (sg_is_chain(&sg))
+		sgp = sg_chain_ptr(&sg);
+
+	return sgp;
+}
+
+static inline struct scatterlist *get_sgp(struct scatterlist **sgs, int i)
+{
+	struct scatterlist *sgp;
+
+	bpf_probe_read_kernel(&sgp, sizeof(sgp), sgs + i);
+	return sgp;
+}
+
+int config = 0;
+int result = 0;
+
+SEC("kprobe/virtqueue_add_sgs")
+int BPF_KPROBE(trace_virtqueue_add_sgs, void *unused, struct scatterlist **sgs,
+	       unsigned int out_sgs, unsigned int in_sgs)
+{
+	struct scatterlist *sgp = NULL;
+	__u64 length1 = 0, length2 = 0;
+	unsigned int i, n, len, upper;
+
+	if (config != 0)
+		return 0;
+
+	upper = out_sgs < VIRTIO_MAX_SGS ? out_sgs : VIRTIO_MAX_SGS;
+	for (i = 0; i < upper; i++) {
+		for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
+		     sgp = __sg_next(sgp)) {
+			bpf_probe_read_kernel(&len, sizeof(len), &sgp->length);
+			length1 += len;
+			n++;
+		}
+	}
+
+	upper = in_sgs < VIRTIO_MAX_SGS ? in_sgs : VIRTIO_MAX_SGS;
+	for (i = 0; i < upper; i++) {
+		for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
+		     sgp = __sg_next(sgp)) {
+			bpf_probe_read_kernel(&len, sizeof(len), &sgp->length);
+			length2 += len;
+			n++;
+		}
+	}
+
+	config = 1;
+	result = length2 - length1;
+	return 0;
+}
-- 
2.34.1