[PATCH 4/6] amdgpu: fix use after free bug related to amdgpu_driver_release_kms()
Shuo Liu
shuox.liu at linux.alibaba.com
Fri Jan 3 07:43:49 UTC 2025
On Fri 3.Jan'25 at 15:02:38 +0800, Gerry Liu wrote:
>
>
>> 2025年1月3日 13:58，Chen, Xiaogang <xiaogang.chen at amd.com> 写道：
>>
>>
>>
>> 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> <mailto:gerry at linux.alibaba.com>
>>> Tested-by: Shuo Liu <shuox.liu at linux.alibaba.com> <mailto: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?
>>
>Per my understanding, `amdgpu_xcp_dev_unplug(adev)` is a workaround for design flaw of the amdgpu_xcp driver.
>Currently the amdgpu_xcp driver assumes everything will go as expected and there’s no failure or GPU hot-lug operations.
>So it only provides an interface `amdgpu_xcp_drm_dev_alloc()` to create xcp devices for a GPU instance, and another interface
>`amdgpu_xcp_drv_release()` to destroy xcp devices for GPU instances. There’s no interface to undo what done by `amdgpu_xcp_drm_dev_alloc()`.
>And I found `amdgpu_xcp_dev_unplug(adev)` can undo work done by `amdgpu_xcp_drm_dev_alloc()`.
>
>So it’s a workaround, the fundamental solution should be to enhance amdgpu_xcp driver to provide interface to unroll work
>done by `amdgpu_xcp_drm_dev_alloc()`.
Agree. Actually, some ops of amdgpu_partition_driver cannot be reused
directly by amd_xcp drm device. DRM doesn't use its minor->dev as
param of such callbacks, just like .release(). When
amdgpu_driver_release_kms() use a amd_xcp drm dev to find the `struct
amdgpu_device *adev`, unexcepted memory accesses.
shuo
>
>The code paths to trigger the use after free are:
>1) in function amdgpu_xcp_dev_alloc(), we allocate a drm_device by calling amdgpu_xcp_drm_dev_alloc(), and then change the device’s driver to amdgpu_partition_driver.
>2) in function amdgpu_xcp_dev_unplug(), it restores drm_device’s driver to the original device driver.
>
>In function amdgpu_driver_load_kms(), if we don’t call amdgpu_xcp_dev_unplug() on error recover path, the `xcp_dev[idx].driver` will still points to amdgpu_partition_driver.
>Later when amdgpu_xcp_drv_release() gets called, it will call platform_device_unregister() -> amdgpu_partition_driver.release -> amdgpu_driver_release_kms().
>Here when amdgpu_driver_release_kms() gets called, the corresponding amdgpu_device object has already been released on error recovery path in function amdgpu_pci_probe().
>
>So just like amdgpu_pci_remove(), we call amdgpu_xcp_gpu_dev_unplug() before calling amdkcl_drm_dev_release().
>> 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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