diff --git a/tools/testing/selftests/bpf/prog_tests/cpumask.c b/tools/testing/selftests/bpf/prog_tests/cpumask.c
index e58a04654238..6185b63b931b 100644
--- a/tools/testing/selftests/bpf/prog_tests/cpumask.c
+++ b/tools/testing/selftests/bpf/prog_tests/cpumask.c
@@ -25,6 +25,9 @@ static const char * const cpumask_success_testcases[] = {
 	"test_global_mask_nested_deep_rcu",
 	"test_global_mask_nested_deep_array_rcu",
 	"test_cpumask_weight",
+	"test_fill_reject_unaligned",
+	"test_fill_reject_small_mask",
+	"test_fill",
 };
 
 static void verify_success(const char *prog_name)
diff --git a/tools/testing/selftests/bpf/progs/cpumask_failure.c b/tools/testing/selftests/bpf/progs/cpumask_failure.c
index b40b52548ffb..acecded8b155 100644
--- a/tools/testing/selftests/bpf/progs/cpumask_failure.c
+++ b/tools/testing/selftests/bpf/progs/cpumask_failure.c
@@ -222,3 +222,41 @@ int BPF_PROG(test_invalid_nested_array, struct task_struct *task, u64 clone_flag
 
 	return 0;
 }
+
+SEC("tp_btf/task_newtask")
+__failure __msg("type=scalar expected=fp")
+int BPF_PROG(test_fill_invalid_destination, struct task_struct *task, u64 clone_flags)
+{
+	struct bpf_cpumask *invalid = (struct bpf_cpumask *)0x123456;
+	u64 bits;
+	int ret;
+
+	ret = bpf_cpumask_fill((struct cpumask *)invalid, &bits, sizeof(bits));
+	if (!ret)
+		err = 2;
+
+	return 0;
+}
+
+SEC("tp_btf/task_newtask")
+__failure __msg("leads to invalid memory access")
+int BPF_PROG(test_fill_invalid_source, struct task_struct *task, u64 clone_flags)
+{
+	void *garbage = (void *)0x123456;
+	struct bpf_cpumask *local;
+	int ret;
+
+	local = create_cpumask();
+	if (!local) {
+		err = 1;
+		return 0;
+	}
+
+	ret = bpf_cpumask_fill((struct cpumask *)local, garbage, 8);
+	if (!ret)
+		err = 2;
+
+	bpf_cpumask_release(local);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/cpumask_success.c b/tools/testing/selftests/bpf/progs/cpumask_success.c
index 80ee469b0b60..ba22878028c1 100644
--- a/tools/testing/selftests/bpf/progs/cpumask_success.c
+++ b/tools/testing/selftests/bpf/progs/cpumask_success.c
@@ -757,6 +757,7 @@ int BPF_PROG(test_refcount_null_tracking, struct task_struct *task, u64 clone_fl
 	mask1 = bpf_cpumask_create();
 	mask2 = bpf_cpumask_create();
 
+
 	if (!mask1 || !mask2)
 		goto free_masks_return;
 
@@ -770,3 +771,116 @@ int BPF_PROG(test_refcount_null_tracking, struct task_struct *task, u64 clone_fl
 		bpf_cpumask_release(mask2);
 	return 0;
 }
+
+SEC("tp_btf/task_newtask")
+__success
+int BPF_PROG(test_fill_reject_small_mask, struct task_struct *task, u64 clone_flags)
+{
+	struct bpf_cpumask *local;
+	u8 toofewbits;
+	int ret;
+
+	local = create_cpumask();
+	if (!local)
+		return 0;
+
+	/* The kfunc should prevent this operation */
+	ret = bpf_cpumask_fill((struct cpumask *)local, &toofewbits, sizeof(toofewbits));
+	if (ret != -EACCES)
+		err = 2;
+
+	bpf_cpumask_release(local);
+
+	return 0;
+}
+
+/* Mask is guaranteed to be large enough for bpf_cpumask_t. */
+#define CPUMASK_TEST_MASKLEN (sizeof(cpumask_t))
+
+/* Add an extra word for the test_fill_reject_unaligned test. */
+u64 bits[CPUMASK_TEST_MASKLEN / 8 + 1];
+extern bool CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS __kconfig __weak;
+
+SEC("tp_btf/task_newtask")
+__success
+int BPF_PROG(test_fill_reject_unaligned, struct task_struct *task, u64 clone_flags)
+{
+	struct bpf_cpumask *mask;
+	char *src;
+	int ret;
+
+	/* Skip if unaligned accesses are fine for this arch.  */
+	if (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
+		return 0;
+
+	mask = bpf_cpumask_create();
+	if (!mask) {
+		err = 1;
+		return 0;
+	}
+
+	/* Misalign the source array by a byte. */
+	src = &((char *)bits)[1];
+
+	ret = bpf_cpumask_fill((struct cpumask *)mask, src, CPUMASK_TEST_MASKLEN);
+	if (ret != -EINVAL)
+		err = 2;
+
+	bpf_cpumask_release(mask);
+
+	return 0;
+}
+
+
+SEC("tp_btf/task_newtask")
+__success
+int BPF_PROG(test_fill, struct task_struct *task, u64 clone_flags)
+{
+	struct bpf_cpumask *mask;
+	bool bit;
+	int ret;
+	int i;
+
+	/* Set only odd bits. */
+	__builtin_memset(bits, 0xaa, CPUMASK_TEST_MASKLEN);
+
+	mask = bpf_cpumask_create();
+	if (!mask) {
+		err = 1;
+		return 0;
+	}
+
+	/* Pass the entire bits array, the kfunc will only copy the valid bits. */
+	ret = bpf_cpumask_fill((struct cpumask *)mask, bits, CPUMASK_TEST_MASKLEN);
+	if (ret) {
+		err = 2;
+		goto out;
+	}
+
+	/*
+	 * Test is there to appease the verifier. We cannot directly
+	 * access NR_CPUS, the upper bound for nr_cpus, so we infer
+	 * it from the size of cpumask_t.
+	 */
+	if (nr_cpus < 0 || nr_cpus >= CPUMASK_TEST_MASKLEN * 8) {
+		err = 3;
+		goto out;
+	}
+
+	bpf_for(i, 0, nr_cpus) {
+		/* Odd-numbered bits should be set, even ones unset. */
+		bit = bpf_cpumask_test_cpu(i, (const struct cpumask *)mask);
+		if (bit == (i % 2 != 0))
+			continue;
+
+		err = 4;
+		break;
+	}
+
+out:
+	bpf_cpumask_release(mask);
+
+	return 0;
+}
+
+#undef CPUMASK_TEST_MASKLEN
