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

[Lucas De Marchi]

On Thu, May 09, 2024 at 12:25:39AM GMT, Lin, Shuicheng wrote:
>Thanks Nirmoy for the review.
>
>Hi all,
>Anything should I do in order to get it merged?
>Thanks.

sorry I had replied but I guess it failed to send and got saved in my
drafts. I just sent it again.

Since it's just a commit message change, if you are ok with the reword,
I can just do it while pushing.

Lucas De Marchi

>
>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;
>> >