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Subject[tip: x86/seves] KVM: SVM: nested: Don't allocate VMCB structures on stack
The following commit has been merged into the x86/seves branch of tip:

Commit-ID: 6ccbd29ade0d159ee1be398dc9defaae567c253d
Gitweb: https://git.kernel.org/tip/6ccbd29ade0d159ee1be398dc9defaae567c253d
Author: Joerg Roedel <jroedel@suse.de>
AuthorDate: Mon, 07 Sep 2020 15:15:02 +02:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Mon, 07 Sep 2020 19:45:24 +02:00

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
---
arch/x86/kvm/svm/nested.c | 47 ++++++++++++++++++++++++++------------
1 file changed, 33 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index fb68467..2803662 100644
--- 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 = {
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