[PATCH] drm/amdgpu: fix NULL pointer access issue when unloading driver

[Zhou1, Tao]

[AMD Public Use]

Reviewed-by: Tao Zhou <tao.zhou1 at amd.com>

> -----Original Message-----
> From: Chen, Guchun <Guchun.Chen at amd.com>
> Sent: Thursday, August 13, 2020 2:45 PM
> To: amd-gfx at lists.freedesktop.org; Zhang, Hawking
> <Hawking.Zhang at amd.com>; Li, Dennis <Dennis.Li at amd.com>; Zhou1, Tao
> <Tao.Zhou1 at amd.com>; Clements, John <John.Clements at amd.com>; Deucher,
> Alexander <Alexander.Deucher at amd.com>
> Cc: Chen, Guchun <Guchun.Chen at amd.com>
> Subject: [PATCH] drm/amdgpu: fix NULL pointer access issue when unloading
> driver
> 
> When unloading driver by "modprobe -r amdgpu", one NULL pointer
> dereference bug occurs in ras debugfs releasing. The cause is the duplicated
> debugfs_remove, as drm debugfs_root dir has been cleaned up already by
> drm_minor_unregister.
> 
> BUG: kernel NULL pointer dereference, address: 00000000000000a0 PGD 0 P4D
> 0
> Oops: 0002 [#1] SMP PTI
> CPU: 11 PID: 1526 Comm: modprobe Tainted: G           OE     5.6.0-guchchen #1
> Hardware name: System manufacturer System Product Name/TUF Z370-PLUS
> GAMING II, BIOS 0411 09/21/2018
> RIP: 0010:down_write+0x15/0x40
> Code: eb de e8 7e 17 72 ff cc cc cc cc cc cc cc cc cc cc cc cc cc cc 0f 1f 44 00 00
> 53 48 89 fb e8 92
> d8 ff ff 31 c0 ba 01 00 00 00 <f0> 48 0f b1 13 75 0f 65 48 8b 04 25 c0 8b 01 00 48
> 89 43 08 5b c3
> RSP: 0018:ffffb1590386fcd0 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: 00000000000000a0 RCX: 0000000000000000
> RDX: 0000000000000001 RSI: ffffffff85b2fcc2 RDI: 00000000000000a0
> RBP: ffffb1590386fd30 R08: ffffffff85b2fcc2 R09: 000000000002b3c0
> R10: ffff97a330618c40 R11: 00000000000005f6 R12: ffff97a3481beb40
> R13: 00000000000000a0 R14: ffff97a3481beb40 R15: 0000000000000000
> FS:  00007fb11a717540(0000) GS:ffff97a376cc0000(0000)
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000000000a0 CR3: 00000004066d6006 CR4: 00000000003606e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call
> Trace:
>  simple_recursive_removal+0x63/0x370
>  ? debugfs_remove+0x60/0x60
>  debugfs_remove+0x40/0x60
>  amdgpu_ras_fini+0x82/0x230 [amdgpu]
>  ? __kernfs_remove.part.17+0x101/0x1f0
>  ? kernfs_name_hash+0x12/0x80
>  amdgpu_device_fini+0x1c0/0x580 [amdgpu]
>  amdgpu_driver_unload_kms+0x3e/0x70 [amdgpu]
>  amdgpu_pci_remove+0x36/0x60 [amdgpu]
>  pci_device_remove+0x3b/0xb0
>  device_release_driver_internal+0xe5/0x1c0
>  driver_detach+0x46/0x90
>  bus_remove_driver+0x58/0xd0
>  pci_unregister_driver+0x29/0x90
>  amdgpu_exit+0x11/0x25 [amdgpu]
>  __x64_sys_delete_module+0x13d/0x210
>  do_syscall_64+0x5f/0x250
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Signed-off-by: Guchun Chen <guchun.chen at amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c
> index 6170d7d28495..35d5bf9e6f6f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c
> @@ -1276,7 +1276,6 @@ void amdgpu_ras_debugfs_remove(struct
> amdgpu_device *adev,
>  	if (!obj || !obj->ent)
>  		return;
> 
> -	debugfs_remove(obj->ent);
>  	obj->ent = NULL;
>  	put_obj(obj);
>  }
> @@ -1290,7 +1289,6 @@ static void amdgpu_ras_debugfs_remove_all(struct
> amdgpu_device *adev)
>  		amdgpu_ras_debugfs_remove(adev, &obj->head);
>  	}
> 
> -	debugfs_remove_recursive(con->dir);
>  	con->dir = NULL;
>  }
>  /* debugfs end */
> --
> 2.17.1