KVM: SVM: nested: Don't allocate VMCB structures on stack

Do not allocate a vmcb_control_area and a vmcb_save_area on the stack,
as these structures will become larger with future extenstions of
SVM and thus the svm_set_nested_state() function will become a too large
stack frame.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-2-joro@8bytes.org

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index fb68467..2803662 100644 (file)
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1060,10 +1060,14 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
        struct vmcb *hsave = svm->nested.hsave;
        struct vmcb __user *user_vmcb = (struct vmcb __user *)
                &user_kvm_nested_state->data.svm[0];
-       struct vmcb_control_area ctl;
-       struct vmcb_save_area save;
+       struct vmcb_control_area *ctl;
+       struct vmcb_save_area *save;
+       int ret;
        u32 cr0;
 
+       BUILD_BUG_ON(sizeof(struct vmcb_control_area) + sizeof(struct vmcb_save_area) >
+                    KVM_STATE_NESTED_SVM_VMCB_SIZE);
+
        if (kvm_state->format != KVM_STATE_NESTED_FORMAT_SVM)
                return -EINVAL;
 
@@ -1095,13 +1099,22 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
                return -EINVAL;
        if (kvm_state->size < sizeof(*kvm_state) + KVM_STATE_NESTED_SVM_VMCB_SIZE)
                return -EINVAL;
-       if (copy_from_user(&ctl, &user_vmcb->control, sizeof(ctl)))
-               return -EFAULT;
-       if (copy_from_user(&save, &user_vmcb->save, sizeof(save)))
-               return -EFAULT;
 
-       if (!nested_vmcb_check_controls(&ctl))
-               return -EINVAL;
+       ret  = -ENOMEM;
+       ctl  = kzalloc(sizeof(*ctl),  GFP_KERNEL);
+       save = kzalloc(sizeof(*save), GFP_KERNEL);
+       if (!ctl || !save)
+               goto out_free;
+
+       ret = -EFAULT;
+       if (copy_from_user(ctl, &user_vmcb->control, sizeof(*ctl)))
+               goto out_free;
+       if (copy_from_user(save, &user_vmcb->save, sizeof(*save)))
+               goto out_free;
+
+       ret = -EINVAL;
+       if (!nested_vmcb_check_controls(ctl))
+               goto out_free;
 
        /*
         * Processor state contains L2 state.  Check that it is
@@ -1109,15 +1122,15 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
         */
        cr0 = kvm_read_cr0(vcpu);
         if (((cr0 & X86_CR0_CD) == 0) && (cr0 & X86_CR0_NW))
-                return -EINVAL;
+               goto out_free;
 
        /*
         * Validate host state saved from before VMRUN (see
         * nested_svm_check_permissions).
         * TODO: validate reserved bits for all saved state.
         */
-       if (!(save.cr0 & X86_CR0_PG))
-               return -EINVAL;
+       if (!(save->cr0 & X86_CR0_PG))
+               goto out_free;
 
        /*
         * All checks done, we can enter guest mode.  L1 control fields
@@ -1126,15 +1139,21 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
         * contains saved L1 state.
         */
        copy_vmcb_control_area(&hsave->control, &svm->vmcb->control);
-       hsave->save = save;
+       hsave->save = *save;
 
        svm->nested.vmcb = kvm_state->hdr.svm.vmcb_pa;
-       load_nested_vmcb_control(svm, &ctl);
+       load_nested_vmcb_control(svm, ctl);
        nested_prepare_vmcb_control(svm);
 
 out_set_gif:
        svm_set_gif(svm, !!(kvm_state->flags & KVM_STATE_NESTED_GIF_SET));
-       return 0;
+
+       ret = 0;
+out_free:
+       kfree(save);
+       kfree(ctl);
+
+       return ret;
 }
 
 struct kvm_x86_nested_ops svm_nested_ops = {