CVE-2022-49781 perf/x86/amd: Fix crash due to race between amd_pmu_enable_all, perf NMI and throttling
A race condition in the Linux kernel's AMD performance monitoring unit can cause a kernel crash, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2022-49781?
CVE-2022-49781 is a medium-severity vulnerability in Linux kernel, published on 1 May 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
perf/x86/amd: Fix crash due to race between amd_pmu_enable_all, perf NMI and throttling
amd_pmu_enable_all() does:
if (!test_bit(idx, cpuc->active_mask)) continue;
amd_pmu_enable_event(cpuc->events[idx]);
A perf NMI of another event can come between these two steps. Perf NMI handler internally disables and enables _all_ events, including the one which nmi-intercepted amd_pmu_enable_all() was in process of enabling. If that unintentionally enabled event has very low sampling period and causes immediate successive NMI, causing the event to be throttled, cpuc->events[idx] and cpuc->active_mask gets cleared by x86_pmu_stop(). This will result in amd_pmu_enable_event() getting called with event=NULL when amd_pmu_enable_all() resumes after handling the NMIs. This causes a kernel crash:
BUG: kernel NULL pointer dereference, address: 0000000000000198 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page [...] Call Trace: <TASK> amd_pmu_enable_all+0x68/0xb0 ctx_resched+0xd9/0x150 event_function+0xb8/0x130 ? hrtimer_start_range_ns+0x141/0x4a0 ? perf_duration_warn+0x30/0x30 remote_function+0x4d/0x60 __flush_smp_call_function_queue+0xc4/0x500 flush_smp_call_function_queue+0x11d/0x1b0 do_idle+0x18f/0x2d0 cpu_startup_entry+0x19/0x20 start_secondary+0x121/0x160 secondary_startup_64_no_verify+0xe5/0xeb </TASK>
amd_pmu_disable_all()/amd_pmu_enable_all() calls inside perf NMI handler were recently added as part of BRS enablement but I'm not sure whether we really need them. We can just disable BRS in the beginning and enable it back while returning from NMI. This will solve the issue by not enabling those events whose active_masks are set but are not yet enabled in hw pmu.
Weakness: CWE-362
Which versions are affected by CVE-2022-49781?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2022-49781?
Apply the vendor's patch.
Is CVE-2022-49781 being exploited?
There is no known exploitation of CVE-2022-49781 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2022-49781, GHSA-76hj-mcwf-qj3w, UBUNTU-CVE-2022-49781.