CVE-2026-72325

What the bug is

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.

Where it lives

The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.

arch/x86/events/amd/core.c

What this is

PERFORMANCE EVENTS SUBSYSTEMMAINTAINERS section matched on arch/*/events/*/* · linux-perf-users@vger.kernel.org · Supported

Check it on the machine

grep -wE 'CONFIG_CPU_SUP_AMD|CONFIG_PERF_EVENTS' /boot/config-$(uname -r)

Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.

Show whether Debian builds this, per release

Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.

• bookwormYnot built on arm64/arm64, arm64/cloud-arm64, arm64/rt/arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le
• trixieYnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
• forky, sidYnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x

Y

built in where it is built at all; some flavours do not build it

Build switches

CONFIG_CPU_SUP_AMD, CONFIG_PERF_EVENTS

Reads as

all on means the file is compiled; any one off means it is not.

From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages

Signals

Published

2026-08-15 (2 months ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.21%, higher than 10.4% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

not yet assignedsource

Subsystem

arch/x86

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
5.19	6.12.97	e9b1a7411a66
5.19	6.18.40	7cc438c99bba
5.19	7.1.5	46d0fd8535ed
5.19	7.2	07c60dda9c05