[PATCH 6.12 065/567] iommufd/selftest: Make it clearer to gcc that the access is not out of bounds

Greg Kroah-Hartman
2026-01-06T17:17:55Z

From: Jason Gunthorpe <jgg@nvidia.com>

[ Upstream commit 5b244b077c0b0e76573fbb9542cf038e42368901 ]

GCC gets a bit confused and reports:

In function '_test_cmd_get_hw_info',
inlined from 'iommufd_ioas_get_hw_info' at iommufd.c:779:3,
inlined from 'wrapper_iommufd_ioas_get_hw_info' at iommufd.c:752:1:
>> iommufd_utils.h:804:37: 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=]
804 | assert(!info->flags);
| ~~~~^~~~~~~
iommufd.c: In function 'wrapper_iommufd_ioas_get_hw_info':
iommufd.c:761:11: note: object 'buffer_smaller' of size 4
761 | } buffer_smaller;
| ^~~~~~~~~~~~~~

While it is true that "struct iommu_test_hw_info[0]" is partly out of
bounds of the input pointer, it is not true that info->flags is out of
bounds. Unclear why it warns on this.

Reuse an existing properly sized stack buffer and pass a truncated length
instead to test the same thing.

Fixes: af4fde93c319 ("iommufd/selftest: Add coverage for IOMMU_GET_HW_INFO ioctl")
Link: https://patch.msgid.link/r/0-v1-63a2cffb09da+4486-iommufd_gcc_bounds_jgg@nvidia.com
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512032344.kaAcKFIM-lkp@intel.com/
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/testing/selftests/iommu/iommufd.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/iommu/iommufd.c b/tools/testing/selftests/iommu/iommufd.c
index b678b24f5a142..6f99268365338 100644
--- a/tools/testing/selftests/iommu/iommufd.c
+++ b/tools/testing/selftests/iommu/iommufd.c
@@ -606,9 +606,6 @@ TEST_F(iommufd_ioas, get_hw_info)
struct iommu_test_hw_info info;
uint64_t trailing_bytes;
} buffer_larger;
- struct iommu_test_hw_info_buffer_smaller {
- __u32 flags;
- } buffer_smaller;

if (self->device_id) {
uint8_t max_pasid = 0;
@@ -640,8 +637,9 @@ TEST_F(iommufd_ioas, get_hw_info)
* the fields within the size range still gets updated.
*/
test_cmd_get_hw_info(self->device_id,
- IOMMU_HW_INFO_TYPE_DEFAULT,
- &buffer_smaller, sizeof(buffer_smaller));
+ IOMMU_HW_INFO_TYPE_DEFAULT, &buffer_exact,
+ offsetofend(struct iommu_test_hw_info,
+ flags));
test_cmd_get_hw_info_pasid(self->device_id, &max_pasid);
ASSERT_EQ(0, max_pasid);
if (variant->pasid_capable) {
--
2.51.0