CVE-2025-40122
perf/x86/intel: Fix IA32_PMC_x_CFG_B MSRs access error
Description
In the Linux kernel, the following vulnerability has been resolved: perf/x86/intel: Fix IA32_PMC_x_CFG_B MSRs access error When running perf_fuzzer on PTL, sometimes the below "unchecked MSR access error" is seen when accessing IA32_PMC_x_CFG_B MSRs. [ 55.611268] unchecked MSR access error: WRMSR to 0x1986 (tried to write 0x0000000200000001) at rIP: 0xffffffffac564b28 (native_write_msr+0x8/0x30) [ 55.611280] Call Trace: [ 55.611282] <TASK> [ 55.611284] ? intel_pmu_config_acr+0x87/0x160 [ 55.611289] intel_pmu_enable_acr+0x6d/0x80 [ 55.611291] intel_pmu_enable_event+0xce/0x460 [ 55.611293] x86_pmu_start+0x78/0xb0 [ 55.611297] x86_pmu_enable+0x218/0x3a0 [ 55.611300] ? x86_pmu_enable+0x121/0x3a0 [ 55.611302] perf_pmu_enable+0x40/0x50 [ 55.611307] ctx_resched+0x19d/0x220 [ 55.611309] __perf_install_in_context+0x284/0x2f0 [ 55.611311] ? __pfx_remote_function+0x10/0x10 [ 55.611314] remote_function+0x52/0x70 [ 55.611317] ? __pfx_remote_function+0x10/0x10 [ 55.611319] generic_exec_single+0x84/0x150 [ 55.611323] smp_call_function_single+0xc5/0x1a0 [ 55.611326] ? __pfx_remote_function+0x10/0x10 [ 55.611329] perf_install_in_context+0xd1/0x1e0 [ 55.611331] ? __pfx___perf_install_in_context+0x10/0x10 [ 55.611333] __do_sys_perf_event_open+0xa76/0x1040 [ 55.611336] __x64_sys_perf_event_open+0x26/0x30 [ 55.611337] x64_sys_call+0x1d8e/0x20c0 [ 55.611339] do_syscall_64+0x4f/0x120 [ 55.611343] entry_SYSCALL_64_after_hwframe+0x76/0x7e On PTL, GP counter 0 and 1 doesn't support auto counter reload feature, thus it would trigger a #GP when trying to write 1 on bit 0 of CFG_B MSR which requires to enable auto counter reload on GP counter 0. The root cause of causing this issue is the check for auto counter reload (ACR) counter mask from user space is incorrect in intel_pmu_acr_late_setup() helper. It leads to an invalid ACR counter mask from user space could be set into hw.config1 and then written into CFG_B MSRs and trigger the MSR access warning. e.g., User may create a perf event with ACR counter mask (config2=0xcb), and there is only 1 event created, so "cpuc->n_events" is 1. The correct check condition should be "i + idx >= cpuc->n_events" instead of "i + idx > cpuc->n_events" (it looks a typo). Otherwise, the counter mask would traverse twice and an invalid "cpuc->assign[1]" bit (bit 0) is set into hw.config1 and cause MSR accessing error. Besides, also check if the ACR counter mask corresponding events are ACR events. If not, filter out these counter mask. If a event is not a ACR event, it could be scheduled to an HW counter which doesn't support ACR. It's invalid to add their counter index in ACR counter mask. Furthermore, remove the WARN_ON_ONCE() since it's easily triggered as user could set any invalid ACR counter mask and the warning message could mislead users.
INFO
Published Date :
Nov. 12, 2025, 11:15 a.m.
Last Modified :
Nov. 12, 2025, 11:15 a.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Affected Products
The following products are affected by CVE-2025-40122
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
Solution
- Update the Linux kernel to the latest version.
- Apply the provided patch for MSR access error.
- Filter invalid auto counter reload counter masks.
- Correct MSR access checks in intel_pmu_acr_late_setup.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2025-40122.
| URL | Resource |
|---|---|
| https://git.kernel.org/stable/c/43796f30507802d93ead2dc44fc9637f34671a89 | |
| https://git.kernel.org/stable/c/c6cca4213b618c92e4972919ee568f0fb87313b1 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2025-40122 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2025-40122
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2025-40122 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2025-40122 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Nov. 12, 2025
Action Type Old Value New Value Added Description In the Linux kernel, the following vulnerability has been resolved: perf/x86/intel: Fix IA32_PMC_x_CFG_B MSRs access error When running perf_fuzzer on PTL, sometimes the below "unchecked MSR access error" is seen when accessing IA32_PMC_x_CFG_B MSRs. [ 55.611268] unchecked MSR access error: WRMSR to 0x1986 (tried to write 0x0000000200000001) at rIP: 0xffffffffac564b28 (native_write_msr+0x8/0x30) [ 55.611280] Call Trace: [ 55.611282] <TASK> [ 55.611284] ? intel_pmu_config_acr+0x87/0x160 [ 55.611289] intel_pmu_enable_acr+0x6d/0x80 [ 55.611291] intel_pmu_enable_event+0xce/0x460 [ 55.611293] x86_pmu_start+0x78/0xb0 [ 55.611297] x86_pmu_enable+0x218/0x3a0 [ 55.611300] ? x86_pmu_enable+0x121/0x3a0 [ 55.611302] perf_pmu_enable+0x40/0x50 [ 55.611307] ctx_resched+0x19d/0x220 [ 55.611309] __perf_install_in_context+0x284/0x2f0 [ 55.611311] ? __pfx_remote_function+0x10/0x10 [ 55.611314] remote_function+0x52/0x70 [ 55.611317] ? __pfx_remote_function+0x10/0x10 [ 55.611319] generic_exec_single+0x84/0x150 [ 55.611323] smp_call_function_single+0xc5/0x1a0 [ 55.611326] ? __pfx_remote_function+0x10/0x10 [ 55.611329] perf_install_in_context+0xd1/0x1e0 [ 55.611331] ? __pfx___perf_install_in_context+0x10/0x10 [ 55.611333] __do_sys_perf_event_open+0xa76/0x1040 [ 55.611336] __x64_sys_perf_event_open+0x26/0x30 [ 55.611337] x64_sys_call+0x1d8e/0x20c0 [ 55.611339] do_syscall_64+0x4f/0x120 [ 55.611343] entry_SYSCALL_64_after_hwframe+0x76/0x7e On PTL, GP counter 0 and 1 doesn't support auto counter reload feature, thus it would trigger a #GP when trying to write 1 on bit 0 of CFG_B MSR which requires to enable auto counter reload on GP counter 0. The root cause of causing this issue is the check for auto counter reload (ACR) counter mask from user space is incorrect in intel_pmu_acr_late_setup() helper. It leads to an invalid ACR counter mask from user space could be set into hw.config1 and then written into CFG_B MSRs and trigger the MSR access warning. e.g., User may create a perf event with ACR counter mask (config2=0xcb), and there is only 1 event created, so "cpuc->n_events" is 1. The correct check condition should be "i + idx >= cpuc->n_events" instead of "i + idx > cpuc->n_events" (it looks a typo). Otherwise, the counter mask would traverse twice and an invalid "cpuc->assign[1]" bit (bit 0) is set into hw.config1 and cause MSR accessing error. Besides, also check if the ACR counter mask corresponding events are ACR events. If not, filter out these counter mask. If a event is not a ACR event, it could be scheduled to an HW counter which doesn't support ACR. It's invalid to add their counter index in ACR counter mask. Furthermore, remove the WARN_ON_ONCE() since it's easily triggered as user could set any invalid ACR counter mask and the warning message could mislead users. Added Reference https://git.kernel.org/stable/c/43796f30507802d93ead2dc44fc9637f34671a89 Added Reference https://git.kernel.org/stable/c/c6cca4213b618c92e4972919ee568f0fb87313b1