[Xen-devel] [PATCH v4 2/3] x86/vvmx: correctly emulate VMWRITE

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

There is an issue with the original __vmwrite() in nested vmx mode:
emulation of a guest's VMWRITE with invalid arguments leads to BUG().

Fix this by using vmwrite_safe() and reporting any kind of VMfail back
to the guest.

A new safe versions of set_vvmcs() macro and related functions are
introduced because of new function signatures and lots of existing
users.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
v3 --> v4:
* VMX_INSN_SUCCEED is used instead of 0
* added TODO comment into set_vvmcs_virtual_safe() based on Andrew's email

 xen/arch/x86/hvm/vmx/vmcs.c        | 12 ++++++++++++
 xen/arch/x86/hvm/vmx/vvmx.c        | 27 ++++++++++++++++++++++++++-
 xen/include/asm-x86/hvm/vmx/vmcs.h |  2 ++
 xen/include/asm-x86/hvm/vmx/vvmx.h |  8 ++++++++
 4 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 0b77dbc..c4ba45e 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -950,6 +950,18 @@ void virtual_vmcs_vmwrite(const struct vcpu *v, u32 
vmcs_encoding, u64 val)
     virtual_vmcs_exit(v);
 }
 
+enum vmx_insn_errno virtual_vmcs_vmwrite_safe(const struct vcpu *v,
+                                              u32 vmcs_encoding, u64 val)
+{
+    enum vmx_insn_errno ret;
+
+    virtual_vmcs_enter(v);
+    ret = vmwrite_safe(vmcs_encoding, val);
+    virtual_vmcs_exit(v);
+
+    return ret;
+}
+
 /*
  * This function is only called in a vCPU's initialization phase,
  * so we can update the posted-interrupt descriptor in non-atomic way.
diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
index 7172621..c5d7262 100644
--- a/xen/arch/x86/hvm/vmx/vvmx.c
+++ b/xen/arch/x86/hvm/vmx/vvmx.c
@@ -305,6 +305,25 @@ void set_vvmcs_real(const struct vcpu *v, u32 encoding, 
u64 val)
     virtual_vmcs_vmwrite(v, encoding, val);
 }
 
+enum vmx_insn_errno set_vvmcs_virtual_safe(void *vvmcs, u32 encoding, u64 val)
+{
+    set_vvmcs_virtual(vvmcs, encoding, val);
+
+    /*
+     * TODO: This should not always succeed. Fields and values need to be
+     * audited against the features offered to the guest in the VT-x MSRs.
+     * This should be fixed when the MSR levelling work is started, at which
+     * point there will be a cpuid_policy-like object.
+     */
+    return VMX_INSN_SUCCEED;
+}
+
+enum vmx_insn_errno set_vvmcs_real_safe(const struct vcpu *v, u32 encoding,
+                                        u64 val)
+{
+    return virtual_vmcs_vmwrite_safe(v, encoding, val);
+}
+
 static unsigned long reg_read(struct cpu_user_regs *regs,
                               enum vmx_regs_enc index)
 {
@@ -1740,13 +1759,19 @@ int nvmx_handle_vmwrite(struct cpu_user_regs *regs)
     unsigned long operand; 
     u64 vmcs_encoding;
     bool_t okay = 1;
+    enum vmx_insn_errno err;
 
     if ( decode_vmx_inst(regs, &decode, &operand, 0)
              != X86EMUL_OKAY )
         return X86EMUL_EXCEPTION;
 
     vmcs_encoding = reg_read(regs, decode.reg2);
-    set_vvmcs(v, vmcs_encoding, operand);
+    err = set_vvmcs_safe(v, vmcs_encoding, operand);
+    if ( err != VMX_INSN_SUCCEED )
+    {
+        vmfail(regs, err);
+        return X86EMUL_OKAY;
+    }
 
     switch ( vmcs_encoding & ~VMCS_HIGH(0) )
     {
diff --git a/xen/include/asm-x86/hvm/vmx/vmcs.h 
b/xen/include/asm-x86/hvm/vmx/vmcs.h
index 005e7e1..1212609 100644
--- a/xen/include/asm-x86/hvm/vmx/vmcs.h
+++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
@@ -539,6 +539,8 @@ void virtual_vmcs_enter(const struct vcpu *);
 void virtual_vmcs_exit(const struct vcpu *);
 u64 virtual_vmcs_vmread(const struct vcpu *, u32 encoding);
 void virtual_vmcs_vmwrite(const struct vcpu *, u32 encoding, u64 val);
+enum vmx_insn_errno virtual_vmcs_vmwrite_safe(const struct vcpu *v,
+                                              u32 vmcs_encoding, u64 val);
 
 static inline int vmx_add_guest_msr(u32 msr)
 {
diff --git a/xen/include/asm-x86/hvm/vmx/vvmx.h 
b/xen/include/asm-x86/hvm/vmx/vvmx.h
index 242e524..e49a000 100644
--- a/xen/include/asm-x86/hvm/vmx/vvmx.h
+++ b/xen/include/asm-x86/hvm/vmx/vvmx.h
@@ -183,6 +183,9 @@ u64 get_vvmcs_virtual(void *vvmcs, u32 encoding);
 u64 get_vvmcs_real(const struct vcpu *, u32 encoding);
 void set_vvmcs_virtual(void *vvmcs, u32 encoding, u64 val);
 void set_vvmcs_real(const struct vcpu *, u32 encoding, u64 val);
+enum vmx_insn_errno set_vvmcs_virtual_safe(void *vvmcs, u32 encoding, u64 val);
+enum vmx_insn_errno set_vvmcs_real_safe(const struct vcpu *, u32 encoding,
+                                        u64 val);
 
 #define get_vvmcs(vcpu, encoding) \
   (cpu_has_vmx_vmcs_shadowing ? \
@@ -194,6 +197,11 @@ void set_vvmcs_real(const struct vcpu *, u32 encoding, u64 
val);
    set_vvmcs_real(vcpu, encoding, val) : \
    set_vvmcs_virtual(vcpu_nestedhvm(vcpu).nv_vvmcx, encoding, val))
 
+#define set_vvmcs_safe(vcpu, encoding, val) \
+  (cpu_has_vmx_vmcs_shadowing ? \
+   set_vvmcs_real_safe(vcpu, encoding, val) : \
+   set_vvmcs_virtual_safe(vcpu_nestedhvm(vcpu).nv_vvmcx, encoding, val))
+
 uint64_t get_shadow_eptp(struct vcpu *v);
 
 void nvmx_destroy_vmcs(struct vcpu *v);
-- 
2.9.3


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