Re: [PATCH v2 5/5] iommu/arm-smmu-v3-test: Fix UBSAN error

[Pranjal Shrivastava <praan@google.com>]

On Thu, Sep 24, 2026 at 08:56:16AM +0000, Mostafa Saleh wrote:
> struct arm_smmu_invs marks its flexible array member inv[] with the
> __counted_by(max_invs).
> 
> arm_smmu_v3_invs_test() uses invs1 to invs5 which has num_invs = 3
> but omit max_invs.
> 
> This causes the following UBSAN error:
> [    2.333240] UBSAN: array-index-out-of-bounds in drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c:1116:21
> [    2.333604]     # arm_smmu_v3_invs_test: lib/ubsan.c:228: array-index-out-of-bounds in drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> [    2.334129] index 1 is out of range for type 'struct arm_smmu_inv[] __counted_by(max_invs)' (aka 'struct arm_smmu_inv[]')
> [    2.335375] CPU: 6 UID: 0 PID: 155 Comm: kunit_try_catch Tainted: G                 N  7.2.0-g8dcb331fbb72 #2 PREEMPT
> [    2.335759] Tainted: [N]=TEST
> [    2.335791] Hardware name: linux,dummy-virt (DT)
> [    2.336254] Call trace:
> [    2.336932]  show_stack+0x18/0x24 (C)
> [    2.338443]  __dump_stack+0x28/0x38
> [    2.338494]  dump_stack_lvl+0x54/0x6c
> [    2.338518]  dump_stack+0x18/0x24
> [    2.338541]  ubsan_epilogue+0x10/0x44
> [    2.338565]  __ubsan_handle_out_of_bounds+0xb8/0xbc
> [    2.338834]  arm_smmu_invs_merge+0x688/0x8ac
> [    2.338862]  arm_smmu_v3_invs_test+0xd4/0x598
> [    2.338890]  kunit_try_run_case+0x64/0x160
> [    2.338914]  kunit_generic_run_threadfn_adapter+0x28/0x4c
> [    2.338955]  kthread+0x10c/0x12c
> [    2.338984]  ret_from_fork+0x10/0x20
> [    2.339433] ---[ end trace ]---
> 
> Explicitly set max_invs = 3 on the test arrays to match the number of
> elements.
> 
> Fixes: 15a2a5645ad7 ("iommu/arm-smmu-v3: Introduce a per-domain arm_smmu_invs array")
> Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Mostafa Saleh <smostafa@google.com>

Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks,
Praan