KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- Fix
- Fixed in 6.6.85, 6.12.21, 6.13.9
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: no
- Technical impact: partial
Summary
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.
Timeline
- CVE published
- CISA SSVC assessment
Exploitation: none · Automatable: no · Technical impact: partial
- Record last updated
Affected versions
- Linux Linux
From c4ab60a86c5ed7c0d727c6dc8cec352e16bc7f90 · fixed in 5289ac43b69c61a49c75720921f2008005a31c43; From d5f7d3833b534f9e43e548461dba1e60aa82f587 · fixed in 04c50cc23a492c4d43fdaefc7c1ecc0ff6f7b82e; From 93ae6b01bafee8fa385aa25ee7ebdb40057f6abe · fixed in 806d5c1e1d2e5502175a24bf70f251648d99c36a; From 93ae6b01bafee8fa385aa25ee7ebdb40057f6abe · fixed in 79e140bba70bcacc5fe15bf8c0b958793fd7d56f; From 93ae6b01bafee8fa385aa25ee7ebdb40057f6abe · fixed in 900b444be493b7f404898c785d6605b177a093d0; From 93ae6b01bafee8fa385aa25ee7ebdb40057f6abe · fixed in fbc7e61195e23f744814e78524b73b59faa54ab4
- Linux Linux
6.2
- KernelLinux
From 6.2.0 · fixed in 6.6.85; From 6.7.0 · fixed in 6.12.21; From 6.13.0 · fixed in 6.13.9