[PATCH 4/6] amdgpu: fix use after free bug related to amdgpu_driver_release_kms()

[Chen, Xiaogang]

On 1/1/2025 11:36 PM, Jiang Liu wrote:
> If some GPU device failed to probe, `rmmod amdgpu` will trigger a use
> after free bug related to amdgpu_driver_release_kms() as:
> 2024-12-26 16:17:45 [16002.085540] BUG: kernel NULL pointer dereference, address: 0000000000000000
> 2024-12-26 16:17:45 [16002.093792] #PF: supervisor read access in kernel mode
> 2024-12-26 16:17:45 [16002.099993] #PF: error_code(0x0000) - not-present page
> 2024-12-26 16:17:45 [16002.106188] PGD 0 P4D 0
> 2024-12-26 16:17:45 [16002.109464] Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI
> 2024-12-26 16:17:45 [16002.115372] CPU: 2 PID: 14375 Comm: rmmod Kdump: loaded Tainted: G        W   E      6.10.0+ #2
> 2024-12-26 16:17:45 [16002.125577] Hardware name: Alibaba Alibaba Cloud ECS/Alibaba Cloud ECS, BIOS 3.0.ES.AL.P.087.05 04/07/2024
> 2024-12-26 16:17:45 [16002.136858] RIP: 0010:drm_sched_fini+0x3f/0xe0 [gpu_sched]
> 2024-12-26 16:17:45 [16002.143463] Code: 60 c6 87 be 00 00 00 01 e8 ce e0 90 d8 48 8d bb 80 00 00 00 e8 c2 e0 90 d8 8b 43 20 85 c0 74 51 45 31 e4 48 8b
> 43 28 4d 63 ec <4a> 8b 2c e8 48 89 ef e8 f5 0e 59 d9 48 8b 45 10 48 8d 55 10 48 39
> 2024-12-26 16:17:45 [16002.164992] RSP: 0018:ffffb570dbbb7da8 EFLAGS: 00010246
> 2024-12-26 16:17:45 [16002.171316] RAX: 0000000000000000 RBX: ffff96b0fdadc878 RCX: 0000000000000000
> 2024-12-26 16:17:46 [16002.179784] RDX: 000fffffffe00000 RSI: 0000000000000000 RDI: ffff96b0fdadc8f8
> 2024-12-26 16:17:46 [16002.188252] RBP: ffff96b0fdadc800 R08: ffff97abbd035040 R09: ffffffff9ac52540
> 2024-12-26 16:17:46 [16002.196722] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> 2024-12-26 16:17:46 [16002.205179] R13: 0000000000000000 R14: ffff96b0fdadfc00 R15: 0000000000000000
> 2024-12-26 16:17:46 [16002.213648] FS:  00007f2737000740(0000) GS:ffff97abbd100000(0000) knlGS:0000000000000000
> 2024-12-26 16:17:46 [16002.223189] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> 2024-12-26 16:17:46 [16002.230103] CR2: 0000000000000000 CR3: 000000011be3a005 CR4: 0000000000f70ef0
> 2024-12-26 16:17:46 [16002.238581] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> 2024-12-26 16:17:46 [16002.247053] DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400
> e024se+0x3c/0x90 [amdxcp]
> 2024-12-26 16:17:46 [16002.337645]  __do_sys_delete_module.constprop.0+0x176/0x310
> 2024-12-26 16:17:46 [16002.344324]  do_syscall_64+0x5d/0x170
> 2024-12-26 16:17:46 [16002.348858]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> 2024-12-26 16:17:46 [16002.354956] RIP: 0033:0x7f2736a620cb-12-26
>
> Fix it by unplugging xcp drm devices when failed to probe GPU devices.
>
> Signed-off-by: Jiang Liu<gerry at linux.alibaba.com>
> Tested-by: Shuo Liu<shuox.liu at linux.alibaba.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c | 4 +++-
>   drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c | 1 +
>   2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> index 5ffe1dad9622..e7f35e3a6d2d 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> @@ -164,8 +164,10 @@ int amdgpu_driver_load_kms(struct amdgpu_device *adev, unsigned long flags)
>   		DRM_WARN("smart shift update failed\n");
>   
>   out:
> -	if (r)
> +	if (r) {
> +		amdgpu_xcp_dev_unplug(adev);
>   		amdgpu_driver_unload_kms(dev);
> +	}
>   

I wonder if you can call amdgpu_xcp_dev_unplug here. It will call 
drm_dev_unplug that unplugs a hotpluggable DRM device. In you case 
amdgpu_driver_load_kms failed during probe time. We need unwind 
amdgpu_driver_load_kms. Why need do unplug a DRM device?

The backtrace show:

2024-12-26 16:17:45 [16002.136858] RIP: 0010:drm_sched_fini+0x3f/0xe0 [gpu_sched]

has:

2024-12-26 16:17:45 [16002.085540] BUG: kernel NULL pointer dereference, address: 0000000000000000

How this change is related to the invalid access above? Can you explain 
more?

Regards

Xiaogang

>   	return r;
>   }
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c
> index a6d456ec6aeb..ef4eaacf67f6 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c
> @@ -382,6 +382,7 @@ void amdgpu_xcp_dev_unplug(struct amdgpu_device *adev)
>   		p_ddev->primary->dev = adev->xcp_mgr->xcp[i].pdev;
>   		p_ddev->driver =  adev->xcp_mgr->xcp[i].driver;
>   		p_ddev->vma_offset_manager = adev->xcp_mgr->xcp[i].vma_offset_manager;
> +		adev->xcp_mgr->xcp[i].ddev = NULL;
>   	}
>   }
>   
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