selftests/bpf: Add test cases for bpf_dynptr_memset()

Add tests to verify the behavior of bpf_dynptr_memset():
  * normal memset 0
  * normal memset non-0
  * memset with an offset
  * memset in dynptr that was adjusted
  * error: size overflow
  * error: offset+size overflow
  * error: readonly dynptr
  * memset into non-linear xdp dynptr

Signed-off-by: Ihor Solodrai <isolodrai@meta.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Mykyta Yatsenko <yatsenko@meta.com>
Link: https://lore.kernel.org/bpf/20250702210309.3115903-3-isolodrai@meta.com

2 files changed, 166 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/dynptr.c b/tools/testing/selftests/bpf/prog_tests/dynptr.c
index 62e7ec775f24..f2b65398afce 100644
--- a/tools/testing/selftests/bpf/prog_tests/dynptr.c
+++ b/tools/testing/selftests/bpf/prog_tests/dynptr.c
@@ -21,6 +21,14 @@ static struct {
 	{"test_dynptr_data", SETUP_SYSCALL_SLEEP},
 	{"test_dynptr_copy", SETUP_SYSCALL_SLEEP},
 	{"test_dynptr_copy_xdp", SETUP_XDP_PROG},
+	{"test_dynptr_memset_zero", SETUP_SYSCALL_SLEEP},
+	{"test_dynptr_memset_notzero", SETUP_SYSCALL_SLEEP},
+	{"test_dynptr_memset_zero_offset", SETUP_SYSCALL_SLEEP},
+	{"test_dynptr_memset_zero_adjusted", SETUP_SYSCALL_SLEEP},
+	{"test_dynptr_memset_overflow", SETUP_SYSCALL_SLEEP},
+	{"test_dynptr_memset_overflow_offset", SETUP_SYSCALL_SLEEP},
+	{"test_dynptr_memset_readonly", SETUP_SKB_PROG},
+	{"test_dynptr_memset_xdp_chunks", SETUP_XDP_PROG},
 	{"test_ringbuf", SETUP_SYSCALL_SLEEP},
 	{"test_skb_readonly", SETUP_SKB_PROG},
 	{"test_dynptr_skb_data", SETUP_SKB_PROG},
diff --git a/tools/testing/selftests/bpf/progs/dynptr_success.c b/tools/testing/selftests/bpf/progs/dynptr_success.c
index a0391f9da2d4..7d7081d05d47 100644
--- a/tools/testing/selftests/bpf/progs/dynptr_success.c
+++ b/tools/testing/selftests/bpf/progs/dynptr_success.c
@@ -681,6 +681,164 @@ out:
 	return XDP_DROP;
 }
 
+char memset_zero_data[] = "data to be zeroed";
+
+SEC("?tp/syscalls/sys_enter_nanosleep")
+int test_dynptr_memset_zero(void *ctx)
+{
+	__u32 data_sz = sizeof(memset_zero_data);
+	char zeroes[32] = {'\0'};
+	struct bpf_dynptr ptr;
+
+	err = bpf_dynptr_from_mem(memset_zero_data, data_sz, 0, &ptr);
+	err = err ?: bpf_dynptr_memset(&ptr, 0, data_sz, 0);
+	err = err ?: bpf_memcmp(zeroes, memset_zero_data, data_sz);
+
+	return 0;
+}
+
+#define DYNPTR_MEMSET_VAL 42
+
+char memset_notzero_data[] = "data to be overwritten";
+
+SEC("?tp/syscalls/sys_enter_nanosleep")
+int test_dynptr_memset_notzero(void *ctx)
+{
+	u32 data_sz = sizeof(memset_notzero_data);
+	struct bpf_dynptr ptr;
+	char expected[32];
+
+	__builtin_memset(expected, DYNPTR_MEMSET_VAL, data_sz);
+
+	err = bpf_dynptr_from_mem(memset_notzero_data, data_sz, 0, &ptr);
+	err = err ?: bpf_dynptr_memset(&ptr, 0, data_sz, DYNPTR_MEMSET_VAL);
+	err = err ?: bpf_memcmp(expected, memset_notzero_data, data_sz);
+
+	return 0;
+}
+
+char memset_zero_offset_data[] = "data to be zeroed partially";
+
+SEC("?tp/syscalls/sys_enter_nanosleep")
+int test_dynptr_memset_zero_offset(void *ctx)
+{
+	char expected[] = "data to \0\0\0\0eroed partially";
+	__u32 data_sz = sizeof(memset_zero_offset_data);
+	struct bpf_dynptr ptr;
+
+	err = bpf_dynptr_from_mem(memset_zero_offset_data, data_sz, 0, &ptr);
+	err = err ?: bpf_dynptr_memset(&ptr, 8, 4, 0);
+	err = err ?: bpf_memcmp(expected, memset_zero_offset_data, data_sz);
+
+	return 0;
+}
+
+char memset_zero_adjusted_data[] = "data to be zeroed partially";
+
+SEC("?tp/syscalls/sys_enter_nanosleep")
+int test_dynptr_memset_zero_adjusted(void *ctx)
+{
+	char expected[] = "data\0\0\0\0be zeroed partially";
+	__u32 data_sz = sizeof(memset_zero_adjusted_data);
+	struct bpf_dynptr ptr;
+
+	err = bpf_dynptr_from_mem(memset_zero_adjusted_data, data_sz, 0, &ptr);
+	err = err ?: bpf_dynptr_adjust(&ptr, 4, 8);
+	err = err ?: bpf_dynptr_memset(&ptr, 0, bpf_dynptr_size(&ptr), 0);
+	err = err ?: bpf_memcmp(expected, memset_zero_adjusted_data, data_sz);
+
+	return 0;
+}
+
+char memset_overflow_data[] = "memset overflow data";
+
+SEC("?tp/syscalls/sys_enter_nanosleep")
+int test_dynptr_memset_overflow(void *ctx)
+{
+	__u32 data_sz = sizeof(memset_overflow_data);
+	struct bpf_dynptr ptr;
+	int ret;
+
+	err = bpf_dynptr_from_mem(memset_overflow_data, data_sz, 0, &ptr);
+	ret = bpf_dynptr_memset(&ptr, 0, data_sz + 1, 0);
+	if (ret != -E2BIG)
+		err = 1;
+
+	return 0;
+}
+
+SEC("?tp/syscalls/sys_enter_nanosleep")
+int test_dynptr_memset_overflow_offset(void *ctx)
+{
+	__u32 data_sz = sizeof(memset_overflow_data);
+	struct bpf_dynptr ptr;
+	int ret;
+
+	err = bpf_dynptr_from_mem(memset_overflow_data, data_sz, 0, &ptr);
+	ret = bpf_dynptr_memset(&ptr, 1, data_sz, 0);
+	if (ret != -E2BIG)
+		err = 1;
+
+	return 0;
+}
+
+SEC("?cgroup_skb/egress")
+int test_dynptr_memset_readonly(struct __sk_buff *skb)
+{
+	struct bpf_dynptr ptr;
+	int ret;
+
+	err = bpf_dynptr_from_skb(skb, 0, &ptr);
+
+	/* cgroup skbs are read only, memset should fail */
+	ret = bpf_dynptr_memset(&ptr, 0, bpf_dynptr_size(&ptr), 0);
+	if (ret != -EINVAL)
+		err = 1;
+
+	return 0;
+}
+
+#define min_t(type, x, y) ({		\
+	type __x = (x);			\
+	type __y = (y);			\
+	__x < __y ? __x : __y; })
+
+SEC("xdp")
+int test_dynptr_memset_xdp_chunks(struct xdp_md *xdp)
+{
+	u32 data_sz, chunk_sz, offset = 0;
+	const int max_chunks = 200;
+	struct bpf_dynptr ptr_xdp;
+	char expected_buf[32];
+	char buf[32];
+	int i;
+
+	__builtin_memset(expected_buf, DYNPTR_MEMSET_VAL, sizeof(expected_buf));
+
+	/* ptr_xdp is backed by non-contiguous memory */
+	bpf_dynptr_from_xdp(xdp, 0, &ptr_xdp);
+	data_sz = bpf_dynptr_size(&ptr_xdp);
+
+	err = bpf_dynptr_memset(&ptr_xdp, 0, data_sz, DYNPTR_MEMSET_VAL);
+	if (err)
+		goto out;
+
+	bpf_for(i, 0, max_chunks) {
+		offset = i * sizeof(buf);
+		if (offset >= data_sz)
+			goto out;
+		chunk_sz = min_t(u32, sizeof(buf), data_sz - offset);
+		err = bpf_dynptr_read(&buf, chunk_sz, &ptr_xdp, offset, 0);
+		if (err)
+			goto out;
+		err = bpf_memcmp(buf, expected_buf, sizeof(buf));
+		if (err)
+			goto out;
+	}
+out:
+	return XDP_DROP;
+}
+
 void *user_ptr;
 /* Contains the copy of the data pointed by user_ptr.
  * Size 384 to make it not fit into a single kernel chunk when copying