On 4/9/21 9:38 AM, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lenda...@amd.com>
>
> Access to the GHCB is mainly in the VMGEXIT path and it is known that the
> GHCB will be mapped. But there are two paths where it is possible the GHCB
> might not be mapped.
>
> The sev_vcpu_deliver_sipi_vector() routine will update the GHCB to inform
> the caller of the AP Reset Hold NAE event that a SIPI has been delivered.
> However, if a SIPI is performed without a corresponding AP Reset Hold,
> then the GHCB might not be mapped (depending on the previous VMEXIT),
> which will result in a NULL pointer dereference.
>
> The svm_complete_emulated_msr() routine will update the GHCB to inform
> the caller of a RDMSR/WRMSR operation about any errors. While it is likely
> that the GHCB will be mapped in this situation, add a safe guard
> in this path to be certain a NULL pointer dereference is not encountered.
>
> Fixes: f1c6366e3043 ("KVM: SVM: Add required changes to support intercepts
> under SEV-ES")
> Fixes: 647daca25d24 ("KVM: SVM: Add support for booting APs in an SEV-ES
> guest")
> Signed-off-by: Tom Lendacky <thomas.lenda...@amd.com>
>
> ---
>
> Changes from v2:
> - Removed WARN_ON_ONCE() from the sev_vcpu_deliver_sipi_vector() path
> since it is guest triggerable and can crash systems with panic_on_warn
> and replaced with pr_warn_once().
I messed up the change-log here, the WARN_ON_ONCE() was dropped and *not*
replaced with a pr_warn_once().
Thanks,
Tom
>
> Changes from v1:
> - Added the svm_complete_emulated_msr() path as suggested by Sean
> Christopherson
> - Add a WARN_ON_ONCE() to the sev_vcpu_deliver_sipi_vector() path
> ---
> arch/x86/kvm/svm/sev.c | 3 +++
> arch/x86/kvm/svm/svm.c | 2 +-
> 2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 83e00e524513..0a539f8bc212 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2105,5 +2105,8 @@ void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu
> *vcpu, u8 vector)
> * the guest will set the CS and RIP. Set SW_EXIT_INFO_2 to a
> * non-zero value.
> */
> + if (!svm->ghcb)
> + return;
> +
> ghcb_set_sw_exit_info_2(svm->ghcb, 1);
> }
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 271196400495..534e52ba6045 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2759,7 +2759,7 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct
> msr_data *msr_info)
> static int svm_complete_emulated_msr(struct kvm_vcpu *vcpu, int err)
> {
> struct vcpu_svm *svm = to_svm(vcpu);
> - if (!sev_es_guest(vcpu->kvm) || !err)
> + if (!err || !sev_es_guest(vcpu->kvm) || WARN_ON_ONCE(!svm->ghcb))
> return kvm_complete_insn_gp(vcpu, err);
>
> ghcb_set_sw_exit_info_1(svm->ghcb, 1);
>
