[Xen-changelog] [xen stable-4.8] x86/vmx: Don't leak host syscall MSR state into HVM guests

[patchbot@xxxxxxx]

commit 6289c3b7c4756bca341ba59e4e246706040f7919
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Mar 14 12:40:36 2017 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Mar 14 12:40:36 2017 +0100

    x86/vmx: Don't leak host syscall MSR state into HVM guests
    
    hvm_hw_cpu->msr_flags is in fact the VMX dirty bitmap of MSRs needing to be
    restored when switching into guest context.  It should never have been part 
of
    the migration state to start with, and Xen must not make any decisions based
    on the value seen during restore.
    
    Identify it as obsolete in the header files, consistently save it as zero 
and
    ignore it on restore.
    
    The MSRs must be considered dirty during VMCS creation to cause the proper
    defaults of 0 to be visible to the guest.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    master commit: 2f1add6e1c8789d979daaafa3d80ddc1bc375783
    master date: 2017-02-21 11:06:39 +0000
---
 xen/arch/x86/hvm/svm/svm.c             | 2 +-
 xen/arch/x86/hvm/vmx/vmcs.c            | 3 +++
 xen/arch/x86/hvm/vmx/vmx.c             | 5 ++---
 xen/include/public/arch-x86/hvm/save.h | 4 ++--
 4 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 37bd6c4..8edc846 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -353,7 +353,7 @@ static void svm_save_cpu_state(struct vcpu *v, struct 
hvm_hw_cpu *data)
     data->msr_cstar        = vmcb->cstar;
     data->msr_syscall_mask = vmcb->sfmask;
     data->msr_efer         = v->arch.hvm_vcpu.guest_efer;
-    data->msr_flags        = -1ULL;
+    data->msr_flags        = 0;
 }
 
 
diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 7879556..4646ecc 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -1104,6 +1104,9 @@ static int construct_vmcs(struct vcpu *v)
             vmx_disable_intercept_for_msr(v, MSR_IA32_BNDCFGS, MSR_TYPE_R | 
MSR_TYPE_W);
     }
 
+    /* All guest MSR state is dirty. */
+    v->arch.hvm_vmx.msr_state.flags = ((1u << VMX_MSR_COUNT) - 1);
+
     /* I/O access bitmap. */
     __vmwrite(IO_BITMAP_A, __pa(d->arch.hvm_domain.io_bitmap));
     __vmwrite(IO_BITMAP_B, __pa(d->arch.hvm_domain.io_bitmap) + PAGE_SIZE);
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 8949ad6..9a42e2e 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -739,13 +739,12 @@ static int vmx_vmcs_restore(struct vcpu *v, struct 
hvm_hw_cpu *c)
 static void vmx_save_cpu_state(struct vcpu *v, struct hvm_hw_cpu *data)
 {
     struct vmx_msr_state *guest_state = &v->arch.hvm_vmx.msr_state;
-    unsigned long guest_flags = guest_state->flags;
 
     data->shadow_gs = v->arch.hvm_vmx.shadow_gs;
     data->msr_cstar = v->arch.hvm_vmx.cstar;
 
     /* save msrs */
-    data->msr_flags        = guest_flags;
+    data->msr_flags        = 0;
     data->msr_lstar        = guest_state->msrs[VMX_INDEX_MSR_LSTAR];
     data->msr_star         = guest_state->msrs[VMX_INDEX_MSR_STAR];
     data->msr_syscall_mask = guest_state->msrs[VMX_INDEX_MSR_SYSCALL_MASK];
@@ -756,7 +755,7 @@ static void vmx_load_cpu_state(struct vcpu *v, struct 
hvm_hw_cpu *data)
     struct vmx_msr_state *guest_state = &v->arch.hvm_vmx.msr_state;
 
     /* restore msrs */
-    guest_state->flags = data->msr_flags & 7;
+    guest_state->flags = ((1u << VMX_MSR_COUNT) - 1);
     guest_state->msrs[VMX_INDEX_MSR_LSTAR]        = data->msr_lstar;
     guest_state->msrs[VMX_INDEX_MSR_STAR]         = data->msr_star;
     guest_state->msrs[VMX_INDEX_MSR_SYSCALL_MASK] = data->msr_syscall_mask;
diff --git a/xen/include/public/arch-x86/hvm/save.h 
b/xen/include/public/arch-x86/hvm/save.h
index 8d73b51..419a3b2 100644
--- a/xen/include/public/arch-x86/hvm/save.h
+++ b/xen/include/public/arch-x86/hvm/save.h
@@ -135,7 +135,7 @@ struct hvm_hw_cpu {
     uint64_t shadow_gs;
 
     /* msr content saved/restored. */
-    uint64_t msr_flags;
+    uint64_t msr_flags; /* Obsolete, ignored. */
     uint64_t msr_lstar;
     uint64_t msr_star;
     uint64_t msr_cstar;
@@ -249,7 +249,7 @@ struct hvm_hw_cpu_compat {
     uint64_t shadow_gs;
 
     /* msr content saved/restored. */
-    uint64_t msr_flags;
+    uint64_t msr_flags; /* Obsolete, ignored. */
     uint64_t msr_lstar;
     uint64_t msr_star;
     uint64_t msr_cstar;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8

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