• Paul Mackerras's avatar
    KVM: PPC: Book3S HV: Restore critical SPRs to host values on guest exit · 4c3bb4cc
    Paul Mackerras authored
    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)
    Cc: stable@vger.kernel.org # v3.14+
    Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
    4c3bb4cc
book3s_hv_rmhandlers.S 74.2 KB