Subject: Re: [PATCH 0/2] Fix SVM hang at startup

From: Paul Mackerras <[email-masked]>
Date: Tue, 24 Mar 2020 13:54:29 +1100

On Fri, Mar 20, 2020 at 11:26:41AM +0100, Laurent Dufour wrote:
> This series is fixing a SVM hang occurring when starting a SVM requiring
> more secure memory than available. The hang happens in the SVM when calling
> UV_ESM.
> 
> The following is happening:
> 
> 1. SVM calls UV_ESM
> 2. Ultravisor (UV) calls H_SVM_INIT_START
> 3. Hypervisor (HV) calls UV_REGISTER_MEM_SLOT
> 4. UV returns error because there is not enough free secure memory
> 5. HV enter the error path in kvmppc_h_svm_init_start()
> 6. In the return path, since kvm->arch.secure_guest is not yet set hrfid is
>    called
> 7. As the HV doesn't know the SVM calling context hrfid is jumping to
>    unknown address in the SVM leading to various expections.
> 
> This series fixes the setting of kvm->arch.secure_guest in
> kvmppc_h_svm_init_start() to ensure that UV_RETURN is called on the return
> path to get back to the UV.
> 
> In addition to ensure that a malicious VM will not call UV reserved Hcall,
> a check of the Secure bit in the calling MSR is addded to reject such a
> call.
> 
> It is assumed that the UV will filtered out such Hcalls made by a malicious
> SVM.
> 
> Laurent Dufour (2):
>   KVM: PPC: Book3S HV: check caller of H_SVM_* Hcalls
>   KVM: PPC: Book3S HV: H_SVM_INIT_START must call UV_RETURN
> 
>  arch/powerpc/kvm/book3s_hv.c       | 32 ++++++++++++++++++++----------
>  arch/powerpc/kvm/book3s_hv_uvmem.c |  3 ++-
>  2 files changed, 23 insertions(+), 12 deletions(-)

Thanks, series applied to my kvm-ppc-next branch.

Paul.