iommufd/selftest: Rework TEST_LENGTH to test min_size explicitly

TEST_LENGTH passing ".size = sizeof(struct _struct) - 1" expects -EINVAL
from "if (ucmd.user_size < op->min_size)" check in iommufd_fops_ioctl().
This has been working when min_size is exactly the size of the structure.

However, if the size of the structure becomes larger than min_size, i.e.
the passing size above is larger than min_size, that min_size sanity no
longer works.

Since the first test in TEST_LENGTH() was to test that min_size sanity
routine, rework it to support a min_size calculation, rather than using
the full size of the structure.

Link: https://lore.kernel.org/r/20231015074648.24185-1-nicolinc@nvidia.comSigned-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

tools/testing/selftests/iommu/iommufd.c

@@ -86,12 +86,13 @@ TEST_F(iommufd, cmd_fail)
 
 TEST_F(iommufd, cmd_length)
 {
-#define TEST_LENGTH(_struct, _ioctl)                                     \
+#define TEST_LENGTH(_struct, _ioctl, _last)                              \
 	{                                                                \
+		size_t min_size = offsetofend(struct _struct, _last);    \
 		struct {                                                 \
 			struct _struct cmd;                              \
 			uint8_t extra;                                   \
-		} cmd = { .cmd = { .size = sizeof(struct _struct) - 1 }, \
+		} cmd = { .cmd = { .size = min_size - 1 },               \
 			  .extra = UINT8_MAX };                          \
 		int old_errno;                                           \
 		int rc;                                                  \
@@ -112,17 +113,19 @@ TEST_F(iommufd, cmd_length)
 		}                                                        \
 	}
 
-	TEST_LENGTH(iommu_destroy, IOMMU_DESTROY);
-	TEST_LENGTH(iommu_hw_info, IOMMU_GET_HW_INFO);
-	TEST_LENGTH(iommu_hwpt_alloc, IOMMU_HWPT_ALLOC);
-	TEST_LENGTH(iommu_ioas_alloc, IOMMU_IOAS_ALLOC);
-	TEST_LENGTH(iommu_ioas_iova_ranges, IOMMU_IOAS_IOVA_RANGES);
-	TEST_LENGTH(iommu_ioas_allow_iovas, IOMMU_IOAS_ALLOW_IOVAS);
-	TEST_LENGTH(iommu_ioas_map, IOMMU_IOAS_MAP);
-	TEST_LENGTH(iommu_ioas_copy, IOMMU_IOAS_COPY);
-	TEST_LENGTH(iommu_ioas_unmap, IOMMU_IOAS_UNMAP);
-	TEST_LENGTH(iommu_option, IOMMU_OPTION);
-	TEST_LENGTH(iommu_vfio_ioas, IOMMU_VFIO_IOAS);
+	TEST_LENGTH(iommu_destroy, IOMMU_DESTROY, id);
+	TEST_LENGTH(iommu_hw_info, IOMMU_GET_HW_INFO, __reserved);
+	TEST_LENGTH(iommu_hwpt_alloc, IOMMU_HWPT_ALLOC, __reserved);
+	TEST_LENGTH(iommu_ioas_alloc, IOMMU_IOAS_ALLOC, out_ioas_id);
+	TEST_LENGTH(iommu_ioas_iova_ranges, IOMMU_IOAS_IOVA_RANGES,
+		    out_iova_alignment);
+	TEST_LENGTH(iommu_ioas_allow_iovas, IOMMU_IOAS_ALLOW_IOVAS,
+		    allowed_iovas);
+	TEST_LENGTH(iommu_ioas_map, IOMMU_IOAS_MAP, iova);
+	TEST_LENGTH(iommu_ioas_copy, IOMMU_IOAS_COPY, src_iova);
+	TEST_LENGTH(iommu_ioas_unmap, IOMMU_IOAS_UNMAP, length);
+	TEST_LENGTH(iommu_option, IOMMU_OPTION, val64);
+	TEST_LENGTH(iommu_vfio_ioas, IOMMU_VFIO_IOAS, __reserved);
 #undef TEST_LENGTH
 }