Patch "KVM: VMX: Don't use vcpu->run->internal.ndata as an array index" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    KVM: VMX: Don't use vcpu->run->internal.ndata as an array index

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-vmx-don-t-use-vcpu-run-internal.ndata-as-an-arra.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit a0af41affce7866fa302f3300d7fdca8e701528b
Author: Reiji Watanabe <reijiw@xxxxxxxxxx>
Date:   Tue Apr 13 15:47:40 2021 +0000

    KVM: VMX: Don't use vcpu->run->internal.ndata as an array index
    
    [ Upstream commit 04c4f2ee3f68c9a4bf1653d15f1a9a435ae33f7a ]
    
    __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>
    Message-Id: <20210413154739.490299-1-reijiw@xxxxxxxxxx>
    Cc: stable@xxxxxxxxxxxxxxx
    Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 0b229282dd50..f8835cabf29f 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6006,19 +6006,19 @@ 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;
 	}