Re: [PATCH v4 1/1] drm/xe: Prevent null pointer access in xe_migrate_copy

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

On 27/09/2024 17:13, Zhanjun Dong wrote:
> xe_migrate_copy designed to copy content of TTM resources. When source
> resource is null, it will trigger a NULL pointer dereference in
> xe_migrate_copy. To avoid this situation, update lacks source flag to
> true for this case, the flag will trigger xe_migrate_clear rather than
> xe_migrate_copy.
> 
> Issue trace:
> <7> [317.089847] xe 0000:00:02.0: [drm:xe_migrate_copy [xe]] Pass 14,
>   sizes: 4194304 & 4194304
> <7> [317.089945] xe 0000:00:02.0: [drm:xe_migrate_copy [xe]] Pass 15,
>   sizes: 4194304 & 4194304
> <1> [317.128055] BUG: kernel NULL pointer dereference, address:
>   0000000000000010
> <1> [317.128064] #PF: supervisor read access in kernel mode
> <1> [317.128066] #PF: error_code(0x0000) - not-present page
> <6> [317.128069] PGD 0 P4D 0
> <4> [317.128071] Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI
> <4> [317.128074] CPU: 1 UID: 0 PID: 1440 Comm: kunit_try_catch Tainted:
>   G     U           N 6.11.0-rc7-xe #1
> <4> [317.128078] Tainted: [U]=USER, [N]=TEST
> <4> [317.128080] Hardware name: Intel Corporation Lunar Lake Client
>   Platform/LNL-M LP5 RVP1, BIOS LNLMFWI1.R00.3221.D80.2407291239 07/29/2024
> <4> [317.128082] RIP: 0010:xe_migrate_copy+0x66/0x13e0 [xe]
> <4> [317.128158] Code: 00 00 48 89 8d e0 fe ff ff 48 8b 40 10 4c 89 85 c8
>   fe ff ff 44 88 8d bd fe ff ff 65 48 8b 3c 25 28 00 00 00 48 89 7d d0 31
>   ff <8b> 79 10 48 89 85 a0 fe ff ff 48 8b 00 48 89 b5 d8 fe ff ff 83 ff
> <4> [317.128162] RSP: 0018:ffffc9000167f9f0 EFLAGS: 00010246
> <4> [317.128164] RAX: ffff8881120d8028 RBX: ffff88814d070428 RCX:
>   0000000000000000
> <4> [317.128166] RDX: ffff88813cb99c00 RSI: 0000000004000000 RDI:
>   0000000000000000
> <4> [317.128168] RBP: ffffc9000167fbb8 R08: ffff88814e7b1f08 R09:
>   0000000000000001
> <4> [317.128170] R10: 0000000000000001 R11: 0000000000000001 R12:
>   ffff88814e7b1f08
> <4> [317.128172] R13: ffff88814e7b1f08 R14: ffff88813cb99c00 R15:
>   0000000000000001
> <4> [317.128174] FS:  0000000000000000(0000) GS:ffff88846f280000(0000)
>   knlGS:0000000000000000
> <4> [317.128176] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> <4> [317.128178] CR2: 0000000000000010 CR3: 000000011f676004 CR4:
>   0000000000770ef0
> <4> [317.128180] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
>   0000000000000000
> <4> [317.128182] DR3: 0000000000000000 DR6: 00000000ffff07f0 DR7:
>   0000000000000400
> <4> [317.128184] PKRU: 55555554
> <4> [317.128185] Call Trace:
> <4> [317.128187]  <TASK>
> <4> [317.128189]  ? show_regs+0x67/0x70
> <4> [317.128194]  ? __die_body+0x20/0x70
> <4> [317.128196]  ? __die+0x2b/0x40
> <4> [317.128198]  ? page_fault_oops+0x15f/0x4e0
> <4> [317.128203]  ? do_user_addr_fault+0x3fb/0x970
> <4> [317.128205]  ? lock_acquire+0xc7/0x2e0
> <4> [317.128209]  ? exc_page_fault+0x87/0x2b0
> <4> [317.128212]  ? asm_exc_page_fault+0x27/0x30
> <4> [317.128216]  ? xe_migrate_copy+0x66/0x13e0 [xe]
> <4> [317.128263]  ? __lock_acquire+0xb9d/0x26f0
> <4> [317.128265]  ? __lock_acquire+0xb9d/0x26f0
> <4> [317.128267]  ? sg_free_append_table+0x20/0x80
> <4> [317.128271]  ? lock_acquire+0xc7/0x2e0
> <4> [317.128273]  ? mark_held_locks+0x4d/0x80
> <4> [317.128275]  ? trace_hardirqs_on+0x1e/0xd0
> <4> [317.128278]  ? _raw_spin_unlock_irqrestore+0x31/0x60
> <4> [317.128281]  ? __pm_runtime_resume+0x60/0xa0
> <4> [317.128284]  xe_bo_move+0x682/0xc50 [xe]
> <4> [317.128315]  ? lock_is_held_type+0xaa/0x120
> <4> [317.128318]  ttm_bo_handle_move_mem+0xe5/0x1a0 [ttm]
> <4> [317.128324]  ttm_bo_validate+0xd1/0x1a0 [ttm]
> <4> [317.128328]  shrink_test_run_device+0x721/0xc10 [xe]
> <4> [317.128360]  ? find_held_lock+0x31/0x90
> <4> [317.128363]  ? lock_release+0xd1/0x2a0
> <4> [317.128365]  ? __pfx_kunit_generic_run_threadfn_adapter+0x10/0x10
>   [kunit]
> <4> [317.128370]  xe_bo_shrink_kunit+0x11/0x20 [xe]
> <4> [317.128397]  kunit_try_run_case+0x6e/0x150 [kunit]
> <4> [317.128400]  ? trace_hardirqs_on+0x1e/0xd0
> <4> [317.128402]  ? _raw_spin_unlock_irqrestore+0x31/0x60
> <4> [317.128404]  kunit_generic_run_threadfn_adapter+0x1e/0x40 [kunit]
> <4> [317.128407]  kthread+0xf5/0x130
> <4> [317.128410]  ? __pfx_kthread+0x10/0x10
> <4> [317.128412]  ret_from_fork+0x39/0x60
> <4> [317.128415]  ? __pfx_kthread+0x10/0x10
> <4> [317.128416]  ret_from_fork_asm+0x1a/0x30
> <4> [317.128420]  </TASK>
> 
> Fixes: 266c85885263 ("drm/xe/xe2: Handle flat ccs move for igfx.")
> Signed-off-by: Zhanjun Dong <zhanjun.dong@intel.com>
> Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>   drivers/gpu/drm/xe/xe_bo.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index 5f2f1ec46b57..5e8f60a8d431 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -682,8 +682,8 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
>   	tt_has_data = ttm && (ttm_tt_is_populated(ttm) ||
>   			      (ttm->page_flags & TTM_TT_FLAG_SWAPPED));
>   
> -	move_lacks_source = handle_system_ccs ? (!bo->ccs_cleared)  :
> -						(!mem_type_is_vram(old_mem_type) && !tt_has_data);
> +	move_lacks_source = !old_mem || (handle_system_ccs ? (!bo->ccs_cleared) :
> +					 (!mem_type_is_vram(old_mem_type) && !tt_has_data));

So is the issue us leaving bo->ccs_cleared set, even after purging the 
object? Seems like when purging the object the bo->ccs_cleared should be 
reset since backing storage is now gone? If we ever have purging for 
real userspace stuff we probably need that anyway.

>   
>   	needs_clear = (ttm && ttm->page_flags & TTM_TT_FLAG_ZERO_ALLOC) ||
>   		(!ttm && ttm_bo->type == ttm_bo_type_device);