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

[Nirmoy Das <nirmoy.das@linux.intel.com>]

+Lucas

On 5/7/2024 3:04 PM, 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 num_fences == 0 case, drm_exec_prepare_obj is the same as drm_exec_lock_obj in
> function, so call drm_exec_lock_obj instead to solve it.
>
> Cc: Nirmoy Das <nirmoy.das@intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>

Reviewed-by: Nirmoy Das <nirmoy.das@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..c5b1694b292f 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_lock_obj(exec, &bo->ttm.base);
>   		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_lock_obj(exec, xe_vm_obj(vm));
>   	if (err)
>   		return err;
>