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Paul Mackerras authored
commit 4c3bb4cc upstream. This restores several special-purpose registers (SPRs) to sane values on guest exit that were missed before. TAR and VRSAVE are readable and writable by userspace, and we need to save and restore them to prevent the guest from potentially affecting userspace execution (not that TAR or VRSAVE are used by any known program that run uses the KVM_RUN ioctl). We save/restore these in kvmppc_vcpu_run_hv() rather than on every guest entry/exit. FSCR affects userspace execution in that it can prohibit access to certain facilities by userspace. We restore it to the normal value for the task on exit from the KVM_RUN ioctl. IAMR is normally 0, and is restored to 0 on guest exit. However, with a radix host on POWER9, it is set to a value that prevents the kernel from executing user-accessible memory. On POWER9, we save IAMR on guest entry and restore it on guest exit to the saved value rather than 0. On POWER8 we continue to set it to 0 on guest exit. PSPB is normally 0. We restore it to 0 on guest exit to prevent userspace taking advantage of the guest having set it non-zero (which would allow userspace to set its SMT priority to high). UAMOR is normally 0. We restore it to 0 on guest exit to prevent the AMR from being used as a covert channel between userspace processes, since the AMR is not context-switched at present. Fixes: b005255e ("KVM: PPC: Book3S HV: Context-switch new POWER8 SPRs", 2014-01-08) Signed-off-by:
Paul Mackerras <paulus@ozlabs.org> Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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