CVE-2026-72325
Received Received - Intake

Kernel BRS Activation Issue in Linux Kernel

Publication date: 2026-08-15

Last updated on: 2026-08-15

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: perf/x86/amd/core: Avoid enabling BRS from the SVM reload path Branch Sampling (BRS) and Last Branch Record (LBR) are mutually exclusive hardware features, and users of both are tracked via cpuc->lbr_users. When SVM is toggled on a CPU, the host perf events are reprogrammed to update the HostOnly filter bit (set when virtualization is enabled, cleared when it is disabled). On PerfMonV2-capable processors, this reprogramming is performed by calling amd_pmu_enable_all() to rewrite the event selectors. However, amd_pmu_enable_all() also calls amd_brs_enable_all(), which enables BRS whenever cpuc->lbr_users > 0. Having active LBR events satisfies this gating on processors that have LBR but not BRS. The kernel then tries to set the BRS enable bit in DebugExtnCfg (MSR 0xc000010f). Since that bit is deprecated on such hardware, the write results in a #GP: Call Trace: <IRQ> amd_pmu_enable_all+0x1d/0x90 amd_pmu_disable_virt+0x62/0xb0 kvm_arch_disable_virtualization_cpu+0xa/0x40 [kvm] hardware_disable_nolock+0x1a/0x30 [kvm] __flush_smp_call_function_queue+0x9b/0x410 __sysvec_call_function+0x18/0xc0 sysvec_call_function+0x69/0x90 </IRQ> <TASK> asm_sysvec_call_function+0x16/0x20 RIP: 0010:cpuidle_enter_state+0xc4/0x450 ? cpuidle_enter_state+0xb7/0x450 cpuidle_enter+0x29/0x40 cpuidle_idle_call+0xf5/0x160 do_idle+0x7b/0xe0 cpu_startup_entry+0x26/0x30 start_secondary+0x115/0x140 secondary_startup_64_no_verify+0x194/0x19b </TASK> Fix this by ensuring that BRS is not enabled from the event selector reprogramming path even when cpuc->lbr_users > 0.

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Meta Information

Published
2026-08-15
Last Modified
2026-08-15
Generated
2026-08-15
AI Q&A
2026-08-15
EPSS Evaluated
N/A
NVD
CVE-2026-72325
EUVD
EUVD-2026-59224

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel occurs when Branch Sampling (BRS) is incorrectly enabled alongside Last Branch Record (LBR) features. When virtualization is toggled, the kernel attempts to reprogram CPU performance events. However, it mistakenly enables BRS even on hardware that does not support it, leading to a general protection fault (#GP) due to writing to a deprecated register.

Detection Guidance

This vulnerability is specific to the Linux kernel's perf/x86/amd/core subsystem and requires kernel-level inspection. Detection involves checking kernel logs for #GP faults during SVM toggling or BRS/LBR state mismatches. Use dmesg | grep -i "general protection" or dmesg | grep -i "brs" to search for related errors.

Impact Analysis

This vulnerability can cause system crashes or instability when virtualization is enabled or disabled on affected CPUs. It may lead to kernel panics or unexpected reboots, disrupting normal operations and potentially causing data loss or service interruptions.

Mitigation Strategies

Apply the latest kernel update from your distribution to patch the issue. If immediate patching is not possible, disable SVM (AMD Secure Virtual Machine) in BIOS/UEFI settings as a temporary workaround. Monitor kernel logs for #GP faults after changes.

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