Re: [PATCH] drm/xe: Prevent BIT() overflow when handling invalid prefetch region

[Matthew Auld <matthew.auld@intel.com>]

On 12/11/2025 00:23, Shuicheng Lin wrote:
> If user provides a large value (such as 0x80) for parameter
> prefetch_mem_region_instance in vm_bind ioctl, it will cause
> BIT(prefetch_region) overflow as below:
> "
>   ------------[ cut here ]------------
>   UBSAN: shift-out-of-bounds in drivers/gpu/drm/xe/xe_vm.c:3414:7
>   shift exponent 128 is too large for 64-bit type 'long unsigned int'
>   CPU: 8 UID: 0 PID: 53120 Comm: xe_exec_system_ Tainted: G        W           6.18.0-rc1-lgci-xe-kernel+ #200 PREEMPT(voluntary)
>   Tainted: [W]=WARN
>   Hardware name: ASUS System Product Name/PRIME Z790-P WIFI, BIOS 0812 02/24/2023
>   Call Trace:
>    <TASK>
>    dump_stack_lvl+0xa0/0xc0
>    dump_stack+0x10/0x20
>    ubsan_epilogue+0x9/0x40
>    __ubsan_handle_shift_out_of_bounds+0x10e/0x170
>    ? mutex_unlock+0x12/0x20
>    xe_vm_bind_ioctl.cold+0x20/0x3c [xe]
>   ...
> "
> Fix it by validating prefetch_region before the BIT() usage.
> 
> Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")

I think should be:

Fixes: c1bb69a2e8e2 ("drm/xe/svm: Consult madvise preferred location in 
prefetch")

And also:

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/6478

> Cc: Matthew Auld <matthew.auld@intel.com>
> Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>

Reviewed-by: Matthew Auld <matthew.auld@intel.com>

An IGT that uses a too large prefetch_region would be good also.

> ---
>   drivers/gpu/drm/xe/xe_vm.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 8fb5cc6a69ec..7cac646bdf1c 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -3411,8 +3411,10 @@ static int vm_bind_ioctl_check_args(struct xe_device *xe, struct xe_vm *vm,
>   				 op == DRM_XE_VM_BIND_OP_PREFETCH) ||
>   		    XE_IOCTL_DBG(xe, prefetch_region &&
>   				 op != DRM_XE_VM_BIND_OP_PREFETCH) ||
> -		    XE_IOCTL_DBG(xe,  (prefetch_region != DRM_XE_CONSULT_MEM_ADVISE_PREF_LOC &&
> -				       !(BIT(prefetch_region) & xe->info.mem_region_mask))) ||
> +		    XE_IOCTL_DBG(xe, (prefetch_region != DRM_XE_CONSULT_MEM_ADVISE_PREF_LOC &&
> +				      /* Guard against undefined shift in BIT(prefetch_region) */
> +				      (prefetch_region >= (sizeof(xe->info.mem_region_mask) * 8) ||
> +				      !(BIT(prefetch_region) & xe->info.mem_region_mask)))) ||
>   		    XE_IOCTL_DBG(xe, obj &&
>   				 op == DRM_XE_VM_BIND_OP_UNMAP) ||
>   		    XE_IOCTL_DBG(xe, (flags & DRM_XE_VM_BIND_FLAG_MADVISE_AUTORESET) &&