[Xen-devel] [PATCH 1/4] x86/vmx: Don't leak host syscall MSR state into HVM guests

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
CC: Kevin Tian <kevin.tian@xxxxxxxxx>
CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
CC: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
---
 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 01c7b58..e09c102 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -348,7 +348,7 @@ 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 0b77dbc..62340bb 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -1090,6 +1090,9 @@ 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 d3d98da..e3694b3 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -779,13 +779,12 @@ 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];
@@ -796,7 +795,7 @@ 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;
-- 
2.1.4


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