Re: [PATCH 04/11] KVM: VMX: Read 32-bit GPR values for ENCLS instructions outside of 64-bit mode

Huang, Kai
2026-04-13T12:19:05Z

On Thu, 2026-04-09 at 16:56 -0700, Sean Christopherson wrote:
> When getting register values for ENCLS emulation, use kvm_register_read()
> instead of kvm_<reg>_read() so that bits 63:32 of the register are dropped
> if the guest is in 32-bit mode.
>
> Note, the misleading/surprising behavior of kvm_<reg>_read() being "raw"
> variants under the hood will be addressed once all non-benign bugs are
> fixed.
>
> Fixes: 70210c044b4e ("KVM: VMX: Add SGX ENCLS[ECREATE] handler to enforce CPUID restrictions")
> Fixes: b6f084ca5538 ("KVM: VMX: Add ENCLS[EINIT] handler to support SGX Launch Control (LC)")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/vmx/sgx.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/sgx.c b/arch/x86/kvm/vmx/sgx.c
> index df1d0cf76947..4c61fc33f764 100644
> --- a/arch/x86/kvm/vmx/sgx.c
> +++ b/arch/x86/kvm/vmx/sgx.c
> @@ -225,8 +225,8 @@ static int handle_encls_ecreate(struct kvm_vcpu *vcpu)
> struct x86_exception ex;
> int r;
>
> - if (sgx_get_encls_gva(vcpu, kvm_rbx_read(vcpu), 32, 32, &pageinfo_gva) ||
> - sgx_get_encls_gva(vcpu, kvm_rcx_read(vcpu), 4096, 4096, &secs_gva))
> + if (sgx_get_encls_gva(vcpu, kvm_register_read(vcpu, VCPU_REGS_RBX), 32, 32, &pageinfo_gva) ||
> + sgx_get_encls_gva(vcpu, kvm_register_read(vcpu, VCPU_REGS_RCX), 4096, 4096, &secs_gva))
> return 1;
>
> /*
> @@ -302,9 +302,9 @@ static int handle_encls_einit(struct kvm_vcpu *vcpu)
> gpa_t sig_gpa, secs_gpa, token_gpa;
> int ret, trapnr;
>
> - if (sgx_get_encls_gva(vcpu, kvm_rbx_read(vcpu), 1808, 4096, &sig_gva) ||
> - sgx_get_encls_gva(vcpu, kvm_rcx_read(vcpu), 4096, 4096, &secs_gva) ||
> - sgx_get_encls_gva(vcpu, kvm_rdx_read(vcpu), 304, 512, &token_gva))
> + if (sgx_get_encls_gva(vcpu, kvm_register_read(vcpu, VCPU_REGS_RBX), 1808, 4096, &sig_gva) ||
> + sgx_get_encls_gva(vcpu, kvm_register_read(vcpu, VCPU_REGS_RCX), 4096, 4096, &secs_gva) ||
> + sgx_get_encls_gva(vcpu, kvm_register_read(vcpu, VCPU_REGS_RDX), 304, 512, &token_gva))
> return 1;
>

Is there any case where bits 63:32 can have non-zero value?

If vCPU is in 32-bit mode then it should not be able to access 64-bit GPR?