[Xen-changelog] [xen stable-4.11] x86/altp2m: make sure EPTP_INDEX is up-to-date when enabling #VE

[patchbot@xxxxxxx]

commit 08cb4b93dd898246131791cd8491ae35c5ef8f55
Author:     George Dunlap <george.dunlap@xxxxxxxxxx>
AuthorDate: Mon Sep 23 14:29:37 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Sep 23 14:29:37 2019 +0200

    x86/altp2m: make sure EPTP_INDEX is up-to-date when enabling #VE
    
    vmx_vmexit_handler() assumes that if
    SECONDARY_EXEC_ENABLE_VIRT_EXCEPTIONS is set, that the value in
    EPTP_INDEX is valid.  Unfortunately, the function which sets this bit
    (vmx_vcpu_update_vmfunc_ve) doesn't actually set EPTP_INDEX; it will
    only be set the next time vmx_vcpu_update_eptp() is called.
    
    This means that if a vcpu makes a vmexit between these two points, the
    EPTP_INDEX it reads will be invalid.  The first time this race happens
    for a domain, EPTP_INDEX will most likely be zero, which is the index
    for the "host" p2m -- and thus is often correct.  But the second time
    this race happens, the value will typically be INVALID_ALTP2M, which
    will hit the following BUG:
    
        BUG_ON(idx >= MAX_ALTP2M);
    
    Worse, if for some reason the current altp2m was *not* `0` during this
    window (say, because a toolstack changed the VM to a different view),
    then the accounting of active vcpus for an altp2m will be thrown off.
    
    Fix this by always updating EPTP_INDEX to the current altp2m index
    when enabling #VE.
    
    Reported-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
    Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
    Reviewed-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
    Tested-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
    Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    master commit: 1dddfff4c39d3db17dfa709b1c57f44e3ed352e3
    master date: 2018-08-02 12:12:43 +0200
---
 xen/arch/x86/hvm/vmx/vmx.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 912903339a..840dc2b44d 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2174,7 +2174,14 @@ static void vmx_vcpu_update_vmfunc_ve(struct vcpu *v)
             mfn = get_gfn_query_unlocked(d, gfn_x(vcpu_altp2m(v).veinfo_gfn), 
&t);
 
             if ( !mfn_eq(mfn, INVALID_MFN) )
+            {
                 __vmwrite(VIRT_EXCEPTION_INFO, mfn_x(mfn) << PAGE_SHIFT);
+                /*
+                 * Make sure we have an up-to-date EPTP_INDEX when
+                 * setting SECONDARY_EXEC_ENABLE_VIRT_EXCEPTIONS.
+                 */
+                __vmwrite(EPTP_INDEX, vcpu_altp2m(v).p2midx);
+            }
             else
                 v->arch.hvm_vmx.secondary_exec_control &=
                     ~SECONDARY_EXEC_ENABLE_VIRT_EXCEPTIONS;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.11

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