[PATCH] drm/xe: Fix UBSAN shift-out-of-bounds failure

[Nirmoy Das]

On 5/7/2024 11:39 AM, Nirmoy Das wrote:
>
>
> On 5/7/2024 10:04 AM, Shuicheng Lin wrote:
>> Here is the failure stack:
>> [   12.988209] ------------[ cut here ]------------
>> [   12.988216] UBSAN: shift-out-of-bounds in ./include/linux/log2.h:57:13
>> [   12.988232] shift exponent 64 is too large for 64-bit type 'long unsigned int'
>> [   12.988235] CPU: 4 PID: 1310 Comm: gnome-shell Tainted: G     U             6.9.0-rc6+prerelease1158+ #19
>> [   12.988237] Hardware name: Intel Corporation Raptor Lake Client Platform/RPL-S ADP-S DDR5 UDIMM CRB, BIOS RPLSFWI1.R00.3301.A02.2208050712 08/05/2022
>> [   12.988239] Call Trace:
>> [   12.988240]  <TASK>
>> [   12.988242]  dump_stack_lvl+0xd7/0xf0
>> [   12.988248]  dump_stack+0x10/0x20
>> [   12.988250]  ubsan_epilogue+0x9/0x40
>> [   12.988253]  __ubsan_handle_shift_out_of_bounds+0x10e/0x170
>> [   12.988260]  dma_resv_reserve_fences.cold+0x2b/0x48
>> [   12.988262]  ? ww_mutex_lock_interruptible+0x3c/0x110
>> [   12.988267]  drm_exec_prepare_obj+0x45/0x60 [drm_exec]
>> [   12.988271]  ? vm_bind_ioctl_ops_execute+0x5b/0x740 [xe]
>> [   12.988345]  vm_bind_ioctl_ops_execute+0x78/0x740 [xe]
>>
>> It is caused by the value 0 of parameter num_fences in function drm_exec_prepare_obj.
>> And lead to in function __rounddown_pow_of_two, "0 - 1" causes the shift-out-of-bounds.
>> For the num_fences, it should be 1 at least.
>>
>> Cc: Matthew Brost<matthew.brost at intel.com>
>> Signed-off-by: Shuicheng Lin<shuicheng.lin at intel.com>
>> ---
>>   drivers/gpu/drm/xe/xe_vm.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
>> index d17192c8b7de..96cb4d9762a3 100644
>> --- a/drivers/gpu/drm/xe/xe_vm.c
>> +++ b/drivers/gpu/drm/xe/xe_vm.c
>> @@ -2692,7 +2692,7 @@ static int vma_lock_and_validate(struct drm_exec *exec, struct xe_vma *vma,
>>   
>>   	if (bo) {
>>   		if (!bo->vm)
>> -			err = drm_exec_prepare_obj(exec, &bo->ttm.base, 0);
>> +			err = drm_exec_prepare_obj(exec, &bo->ttm.base, 1);
>
> This needs to be fixed in drm_exec_prepare_obj() by checking 
> num_fences and not calling dma_resv_reserve_fences()
>
or just call drm_exec_lock_obj() here. ref: 
https://patchwork.freedesktop.org/patch/577487/

Nirmoy

>
> Regards,
>
> Nirmoy
>
>>   		if (!err && validate)
>>   			err = xe_bo_validate(bo, xe_vma_vm(vma), true);
>>   	}
>> @@ -2777,7 +2777,7 @@ static int vm_bind_ioctl_ops_lock_and_prep(struct drm_exec *exec,
>>   	struct xe_vma_op *op;
>>   	int err;
>>   
>> -	err = drm_exec_prepare_obj(exec, xe_vm_obj(vm), 0);
>> +	err = drm_exec_prepare_obj(exec, xe_vm_obj(vm), 1);
>>   	if (err)
>>   		return err;
>>   
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