Commit 338c7dbadd26 ("KVM: Improve create VCPU parameter (CVE-2013-4587)")
introduced a check to prevent potential kernel memory corruption in case
the vcpu id is too great.
Unfortunately this check assumes vcpu ids grow in sequence with a common
difference of 1, which is wrong: archs are free to use vcpu id as they fit.
For example, QEMU originated vcpu ids for PowerPC cpus running in boot3s_hv
mode, can grow with a common difference of 2, 4 or 8: if KVM_MAX_VCPUS is
1024, guests may be limited down to 128 vcpus on POWER8.
This means the check does not belong here and should be moved to some arch
specific function: kvm_arch_vcpu_create() looks like a good candidate.
ARM and s390 already have such a check.
I could not spot any path in the PowerPC or common KVM code where a vcpu
id is used as described in the above commit: I believe PowerPC can live
without this check.
In the end, this patch simply moves the check to MIPS and x86.
Signed-off-by: Greg Kurz <gkurz@xxxxxxxxxxxxxxxxxx>
---
arch/mips/kvm/mips.c | 3 +++
arch/x86/kvm/x86.c | 3 +++
virt/kvm/kvm_main.c | 3 ---
3 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 70ef1a43c114..ce3f1e8a8b3f 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -251,6 +251,9 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
struct kvm_vcpu *vcpu = kzalloc(sizeof(struct kvm_vcpu), GFP_KERNEL);
+ if (id >= KVM_MAX_VCPUS)
+ return -EINVAL;
+
if (!vcpu) {
err = -ENOMEM;
goto out;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9b7798c7b210..f705d57b12ed 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7358,6 +7358,9 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
{
struct kvm_vcpu *vcpu;
+ if (id >= KVM_MAX_VCPUS)
+ return -EINVAL;
+
if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
printk_once(KERN_WARNING
"kvm: SMP vm created on host with unstable TSC; "
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4fd482fb9260..6b6cca3cb488 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2272,9 +2272,6 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
int r;
struct kvm_vcpu *vcpu;
- if (id >= KVM_MAX_VCPUS)
- return -EINVAL;
-
vcpu = kvm_arch_vcpu_create(kvm, id);
if (IS_ERR(vcpu))
return PTR_ERR(vcpu);
