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CVE-2022-49559 — KVM: x86: Drop WARNs that assert a triple fault never "escapes" from L2

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

KVM: x86: Drop WARNs that assert a triple fault never "escapes" from L2

Remove WARNs that sanity check that KVM never lets a triple fault for L2 escape and incorrectly end up in L1. In normal operation, the sanity check is perfectly valid, but it incorrectly assumes that it's impossible for userspace to induce KVM_REQ_TRIPLE_FAULT without bouncing through KVM_RUN (which guarantees kvm_check_nested_state() will see and handle the triple fault).

The WARN can currently be triggered if userspace injects a machine check while L2 is active and CR4.MCE=0. And a future fix to allow save/restore of KVM_REQ_TRIPLE_FAULT, e.g. so that a synthesized triple fault isn't lost on migration, will make it trivially easy for userspace to trigger the WARN.

Clearing KVM_REQ_TRIPLE_FAULT when forcibly leaving guest mode is tempting, but wrong, especially if/when the request is saved/restored, e.g. if userspace restores events (including a triple fault) and then restores nested state (which may forcibly leave guest mode). Ignoring the fact that KVM doesn't currently provide the necessary APIs, it's userspace's responsibility to manage pending events during save/restore.

------------[ cut here ]------------ WARNING: CPU: 7 PID: 1399 at arch/x86/kvm/vmx/nested.c:4522 nested_vmx_vmexit+0x7fe/0xd90 [kvm_intel] Modules linked in: kvm_intel kvm irqbypass CPU: 7 PID: 1399 Comm: state_test Not tainted 5.17.0-rc3+ #808 Ha…

RHSA-2022:7683 — Red Hat Security Advisory: kernel security, bug fix, and enhancement update

kernel: off-path attacker may inject data or terminate victim's TCP session kernel: race condition in VT_RESIZEX ioctl when vc_cons[i].d is already NULL leading to NULL pointer dereference kernel: use-after-free vulnerability in function sco_sock_sendmsg() kernel: memory leak for large arguments in video_usercopy function in drivers/media/v4l2-core/v4l2-ioctl.c kernel: mm/damon/dbgfs: protect targets destructions with kdamond_lock kernel: mm/hwpoison: clear MF_COUNT_INCREASED before retrying get_any_page() kernel: veth: ensure skb entering GRO are not cloned. kernel: inet: fully convert sk->sk_rx_dst to RCU rules kernel: NFSD: Fix READDIR buffer overflow kernel: cpufreq: CPPC: Fix potential memleak in cppc_cpufreq_cpu_init kernel: nvme-rdma: destroy cm id before destroy qp to avoid use after free kernel: regmap: Fix possible double-free in regcache_rbtree_exit() kernel: ethtool: do not perform operations on net devices being unregistered kernel: scsi: scsi_debug: Fix type in min_t to avoid stack OOB kernel: KVM: x86/mmu: Zap _all_ roots when unmapping gfn range in TDP MMU kernel: udmabuf: validate ubuf->pagecount kernel: drm/virtio: Ensure that objs is not NULL in virtio_gpu_array_put_free() kernel: smb2_ioctl_query_info NULL pointer dereference kernel: NULL pointer dereference in udf_expand_file_adinicbdue() during writeback kernel: swiotlb information leak with DMA_FROM_DEVICE kernel: uninitialized registers on stack in nft_do_chain can cause kernel pointer leakage to UM k…