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

[Lin, Shuicheng]

Thanks Nirmoy for the review.

Hi all,
Anything should I do in order to get it merged?
Thanks.

Best Regards
Shuicheng

> -----Original Message-----
> From: Nirmoy Das <nirmoy.das at linux.intel.com>
> Sent: Tuesday, May 7, 2024 11:13 PM
> To: Lin, Shuicheng <shuicheng.lin at intel.com>; intel-xe at lists.freedesktop.org
> Cc: Das, Nirmoy <nirmoy.das at intel.com>; Brost, Matthew
> <matthew.brost at intel.com>; De Marchi, Lucas <lucas.demarchi at intel.com>
> Subject: Re: [PATCH] drm/xe: Fix UBSAN shift-out-of-bounds failure
> 
> +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 at intel.com>
> > Cc: Matthew Brost <matthew.brost at intel.com>
> > Signed-off-by: Shuicheng Lin <shuicheng.lin at intel.com>
> 
> Reviewed-by: Nirmoy Das <nirmoy.das 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..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;
> >