CVE-2025-22013 Information

Description

In the Linux kernel the following vulnerability has been resolved:

KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state

There are several problems with the way hyp code lazily saves the host’s FPSIMD/SVE state including:

Host SVE being discarded unexpectedly due to inconsistent configuration of TIF_SVE and CPACR_ELx.ZEN. This has been seen to result in QEMU crashes where SVE is used by memmove() as reported by Eric Auger:

https://issues.redhat.com/browse/RHEL-68997

Host SVE state is discarded after modification by ptrace which was an unintentional ptrace ABI change introduced with lazy discarding of SVE state.

The host FPMR value can be discarded when running a non-protected VM where FPMR support is not exposed to a VM and that VM uses FPSIMD/SVE. In these cases the hyp code does not save the host’s FPMR before unbinding the host’s FPSIMD/SVE/SME state leaving a stale value in memory.

Avoid these by eagerly saving and lushing\ the host’s FPSIMD/SVE/SME state when loading a vCPU such that KVM does not need to save any of the host’s FPSIMD/SVE/SME state. For clarity fpsimd_kvm_prepare() is removed and the necessary call to fpsimd_save_and_flush_cpu_state() is placed in kvm_arch_vcpu_load_fp(). As ‘fpsimd_state’ and ‘fpmr_ptr’ should not be used they are set to NULL; all uses of these will be removed in subsequent patches.

Historical problems go back at least as far as v5.17 e.g. erroneous assumptions about TIF_SVE being clear in commit:

8383741ab2e773a9 (\KVM: arm64: Get rid of host SVE tracking/saving)

… and so this eager save+flush probably needs to be backported to ALL stable trees.

Reference

https://git.kernel.org/stable/c/79e140bba70bcacc5fe15bf8c0b958793fd7d56f https://git.kernel.org/stable/c/806d5c1e1d2e5502175a24bf70f251648d99c36a https://git.kernel.org/stable/c/900b444be493b7f404898c785d6605b177a093d0 https://git.kernel.org/stable/c/fbc7e61195e23f744814e78524b73b59faa54ab4