CVE-2025-21876 Information

Description

In the Linux kernel the following vulnerability has been resolved:

iommu/vt-d: Fix suspicious RCU usage

Commit (\iommu/vt-d: Allocate DMAR fault interrupts locally) moved the call to enable_drhd_fault_handling() to a code path that does not hold any lock while traversing the drhd list. Fix it by ensuring the dmar_global_lock lock is held when traversing the drhd list.

Without this fix the following warning is triggered:

WARNING: suspicious RCU usage 6.14.0-rc3 55 Not tainted

drivers/iommu/intel/dmar.c:2046 RCU-list traversed in non-reader section!! other info that might help us debug this: rcu_scheduler_active = 1 debug_locks = 1 2 locks held by cpuhp/1/23: 0: ffffffff84a67c50 (cpu_hotplug_lock)++++-0:0 at: cpuhp_thread_fun+0x87/0x2c0 1: ffffffff84a6a380 (cpuhp_state-up)+.+.-0:0 at: cpuhp_thread_fun+0x87/0x2c0 stack backtrace: CPU: 1 UID: 0 PID: 23 Comm: cpuhp/1 Not tainted 6.14.0-rc3 55 Call Trace: dump_stack_lvl+0xb7/0xd0 lockdep_rcu_suspicious+0x159/0x1f0 ? __pfx_enable_drhd_fault_handling+0x10/0x10 enable_drhd_fault_handling+0x151/0x180 cpuhp_invoke_callback+0x1df/0x990 cpuhp_thread_fun+0x1ea/0x2c0 smpboot_thread_fn+0x1f5/0x2e0 ? __pfx_smpboot_thread_fn+0x10/0x10 kthread+0x12a/0x2d0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x4a/0x60 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30

Holding the lock in enable_drhd_fault_handling() triggers a lockdep splat about a possible deadlock between dmar_global_lock and cpu_hotplug_lock. This is avoided by not holding dmar_global_lock when calling iommu_device_register() which initiates the device probe process.

Reference

https://git.kernel.org/stable/c/4117c72938493a77ab53cc4b8284be8fb6ec8065 https://git.kernel.org/stable/c/b150654f74bf0df8e6a7936d5ec51400d9ec06d8 https://git.kernel.org/stable/c/c603ccbe91d189849e1439134598ec567088dcec