Fix a class of bugs (limited to nested VMX, as far as we know) where KVM can corrupt an unrelated process' memory if KVM (attempts to) write to guest memory during VM destruction. Because current->mm usually isn't kvm->mm when a VM is dying, e.g. because the associated kvm->mm process has already exited, writing to what KVM thinks is guest memory will corrupt the current address space if the associated userspace address happens to be writable in the victim.
Patch 1 is a blanket fix for the uaccess paths. AFAIK, x86's nVMX is the only path in KVM that screws up, but auditing kvm_arch_destroy_vm() proved to be infeasible for a human (I didn't throw AI at it, yet...), and I can't think of any downsides to going straight to a broader fix. Patch 2 fixes what I assume is a blatant PPC bug. KVM PPC completely ignores kvm_arch_flush_shadow_all(), i.e. AFAICT, doesn't tear down its page tables when the owning process exits. I don't have much confidence in the "fix", in part because it seems impossible that such a blatant bug could have gone unnoticed, but also because I went with a very naive approach of invoking kvm_arch_flush_shadow_memslot() for each memslot. The changelog is pretty sparse, because I didn't know how to describe the issue byeond "this is completely broken". Patches 3-5 implement more agressive hardening to nuke the memslots before calling kvm_arch_destroy_vm(), e.g. to guard against writing to guest memory during kvm_arch_destroy_vm() without going through uaccess. Setting dummy memslots feels a little hacky, but kvm_arch_flush_shadow_all() should have purged everything that effectively caches memslots, so it seems like the right approach? The remaining patches fudge around the nVMX bugs (KVM abuses its nested VM-Exit flow to forcefully take a vCPU out of L2, which has been an endless source of pain, but is also equally difficult to fix properly), and add more hardening to detect KVM bugs (though the uaccess+memslot changes earlier in the series should render any bugs benign). v1: https://lore.kernel.org/all/[email protected] Jim Mattson (1): KVM: nVMX: Don't flush shadow VMCS12 to guest memory during vCPU teardown Sean Christopherson (9): KVM: Reject user accesses to guest memory if current->mm != kvm->mm KVM: PPC: Flush/zap all memslots on kvm_arch_flush_shadow_all() KVM: x86: Unmap VMAs for KVM-internal memslots when the memslot is freed KVM: Disallow setting memslots when the VM is being destroyed KVM: Destroy memslots immediately after mmu_notifiers are unregistered KVM: WARN if KVM attempts to do guest-related uaccess with "wrong" process KVM: WARN and reject guest-based uaccess if VM is dying KVM: nVMX: Don't try to load eVMCS12 page when the VM is dying KVM: Pre-check uaccesses in KVM's APIs to read/write guest memory arch/powerpc/include/asm/kvm_host.h | 1 - arch/powerpc/kvm/powerpc.c | 11 ++++ arch/x86/kvm/vmx/nested.c | 14 ++++- arch/x86/kvm/vmx/sgx.c | 2 +- arch/x86/kvm/vmx/vmx.c | 8 +-- arch/x86/kvm/x86.c | 36 +++++------- include/linux/kvm_host.h | 30 +++++++++- virt/kvm/kvm_main.c | 87 +++++++++++++++++++---------- 8 files changed, 126 insertions(+), 63 deletions(-) base-commit: d4b7fb647204f0c81dfeae2d1a708e4d858e0c94 -- 2.56.0.rc1.315.gc6ed9934b7-goog
