> 2025年1月3日 13:58，Chen, Xiaogang <[email protected]> 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 <[email protected]> >> <mailto:[email protected]> >> Tested-by: Shuo Liu <[email protected]> >> <mailto:[email protected]> >> --- >> 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()`. 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; >> } >> } >>
