CVE-2025-22013

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 "flushing" 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.