GCC warns about potential out-of-bounds access when the test provides a buffer smaller than struct iommu_test_hw_info:

iommufd_utils.h:817:37: warning: array subscript 'struct iommu_test_hw_info[0]' is partly outside array bounds of 'struct iommu_test_hw_info_buffer_smaller[1]' [-Warray-bounds=] 817 | assert(!info->flags); | ~~~~^~~~~~~

The warning occurs because 'info' is cast to a pointer to the full 8-byte struct at the top of the function, but the buffer_smaller test case passes only a 4-byte buffer. While the code correctly checks data_len before accessing each field, GCC's flow analysis with inlining doesn't recognize that the size check protects the access.

Fix this by accessing fields through appropriately-typed pointers that match the actual field sizes (__u32), declared only after the bounds check. This makes the relationship between the size check and memory access explicit to the compiler.

Signed-off-by: Nirbhay Sharma nirbhay.lkd@gmail.com --- tools/testing/selftests/iommu/iommufd_utils.h | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/iommu/iommufd_utils.h b/tools/testing/selftests/iommu/iommufd_utils.h index 9f472c20c190..37c1b994008c 100644 --- a/tools/testing/selftests/iommu/iommufd_utils.h +++ b/tools/testing/selftests/iommu/iommufd_utils.h @@ -770,7 +770,6 @@ static int _test_cmd_get_hw_info(int fd, __u32 device_id, __u32 data_type, void *data, size_t data_len, uint32_t *capabilities, uint8_t *max_pasid) { - struct iommu_test_hw_info *info = (struct iommu_test_hw_info *)data; struct iommu_hw_info cmd = { .size = sizeof(cmd), .dev_id = device_id, @@ -810,11 +809,19 @@ static int _test_cmd_get_hw_info(int fd, __u32 device_id, __u32 data_type, } }

- if (info) { - if (data_len >= offsetofend(struct iommu_test_hw_info, test_reg)) - assert(info->test_reg == IOMMU_HW_INFO_SELFTEST_REGVAL); - if (data_len >= offsetofend(struct iommu_test_hw_info, flags)) - assert(!info->flags); + if (data) { + if (data_len >= offsetofend(struct iommu_test_hw_info, + test_reg)) { + __u32 *test_reg = (__u32 *)data + 1; + + assert(*test_reg == IOMMU_HW_INFO_SELFTEST_REGVAL); + } + if (data_len >= offsetofend(struct iommu_test_hw_info, + flags)) { + __u32 *flags = data; + + assert(!*flags); + } }

if (max_pasid)