On 13/04/21 17:47, Reiji Watanabe wrote:
__vmx_handle_exit() uses vcpu->run->internal.ndata as an index for
an array access. Since vcpu->run is (can be) mapped to a user address
space with a writer permission, the 'ndata' could be updated by the
user process at anytime (the user process can set it to outside the
bounds of the array).
So, it is not safe that __vmx_handle_exit() uses the 'ndata' that way.
Fixes: 1aa561b1a4c0 ("kvm: x86: Add "last CPU" to some KVM_EXIT information")
Signed-off-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
---
arch/x86/kvm/vmx/vmx.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
Ouch. In theory it's an internal error, but we've seen it happen on
problematic hardware. Should we consider it a security issue?
Paolo
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 32cf8287d4a7..29b40e092d13 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6027,19 +6027,19 @@ static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
exit_reason.basic != EXIT_REASON_PML_FULL &&
exit_reason.basic != EXIT_REASON_APIC_ACCESS &&
exit_reason.basic != EXIT_REASON_TASK_SWITCH)) {
+ int ndata = 3;
+
vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_DELIVERY_EV;
- vcpu->run->internal.ndata = 3;
vcpu->run->internal.data[0] = vectoring_info;
vcpu->run->internal.data[1] = exit_reason.full;
vcpu->run->internal.data[2] = vcpu->arch.exit_qualification;
if (exit_reason.basic == EXIT_REASON_EPT_MISCONFIG) {
- vcpu->run->internal.ndata++;
- vcpu->run->internal.data[3] =
+ vcpu->run->internal.data[ndata++] =
vmcs_read64(GUEST_PHYSICAL_ADDRESS);
}
- vcpu->run->internal.data[vcpu->run->internal.ndata++] =
- vcpu->arch.last_vmentry_cpu;
+ vcpu->run->internal.data[ndata++] = vcpu->arch.last_vmentry_cpu;
+ vcpu->run->internal.ndata = ndata;
return 0;
}
