[PATCH v2 4/5] vVMX: operand size in decode_vmx_inst()

[Jan Beulich <jbeulich@xxxxxxxx>]

Address size is entirely irrelevant to operand size determination; For
VMREAD and VMWRITE outside of 64-bit mode operand size is 32 bits, while
in 64-bit mode it's (naturally) 64 bits. For all other insns it's 64
bits (a physical address) or 128 bits (INVEPT, INVVPID). To limit the
amount of change here, keep the latter at reading only 64 bits from
guest space.

Fixes: 09fce8016596 ("Nested VMX: Emulation of guest VMXON/OFF instruction")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Beyond the wrong operand handling for INVEPT and INVVPID, the latter
also doesn't even have the part read checked to have bits 16 and above
all clear.

--- a/xen/arch/x86/hvm/vmx/vvmx.c
+++ b/xen/arch/x86/hvm/vmx/vvmx.c
@@ -411,13 +411,13 @@ static inline u32 __n2_secondary_exec_co
 
 static int decode_vmx_inst(struct cpu_user_regs *regs,
                            struct vmx_inst_decoded *decode,
-                           unsigned long *poperandS)
+                           unsigned long *poperandS, unsigned int size)
 {
     struct vcpu *v = current;
     union vmx_inst_info info;
     struct segment_register seg;
     unsigned long base, index, seg_base, disp, offset;
-    int scale, size;
+    unsigned int scale;
 
     __vmread(VMX_INSTRUCTION_INFO, &offset);
     info.word = offset;
@@ -449,7 +449,8 @@ static int decode_vmx_inst(struct cpu_us
 
         __vmread(EXIT_QUALIFICATION, &disp);
 
-        size = 1 << (info.fields.addr_size + 1);
+        if ( !size )
+            size = 4 << mode_64bit;
 
         offset = base + index * scale + disp;
         base = !mode_64bit || info.fields.segment >= x86_seg_fs ?
@@ -464,7 +465,9 @@ static int decode_vmx_inst(struct cpu_us
         if ( poperandS != NULL )
         {
             pagefault_info_t pfinfo;
-            int rc = hvm_copy_from_guest_linear(poperandS, base, size,
+            int rc = hvm_copy_from_guest_linear(poperandS, base,
+                                                min_t(unsigned int, size,
+                                                      sizeof(*poperandS)),
                                                 0, &pfinfo);
 
             if ( rc == HVMTRANS_bad_linear_to_gfn )
@@ -1561,7 +1564,7 @@ static int nvmx_handle_vmxon(struct cpu_
     uint32_t nvmcs_revid;
     int rc;
 
-    rc = decode_vmx_inst(regs, &decode, &gpa);
+    rc = decode_vmx_inst(regs, &decode, &gpa, sizeof(gpa));
     if ( rc != X86EMUL_OKAY )
         return rc;
 
@@ -1788,7 +1791,7 @@ static int nvmx_handle_vmptrld(struct cp
     unsigned long gpa = 0;
     int rc;
 
-    rc = decode_vmx_inst(regs, &decode, &gpa);
+    rc = decode_vmx_inst(regs, &decode, &gpa, sizeof(gpa));
     if ( rc != X86EMUL_OKAY )
         return rc;
 
@@ -1865,7 +1868,7 @@ static int nvmx_handle_vmptrst(struct cp
     unsigned long gpa = 0;
     int rc;
 
-    rc = decode_vmx_inst(regs, &decode, &gpa);
+    rc = decode_vmx_inst(regs, &decode, &gpa, sizeof(gpa));
     if ( rc != X86EMUL_OKAY )
         return rc;
 
@@ -1891,7 +1894,7 @@ static int nvmx_handle_vmclear(struct cp
     void *vvmcs;
     int rc;
 
-    rc = decode_vmx_inst(regs, &decode, &gpa);
+    rc = decode_vmx_inst(regs, &decode, &gpa, sizeof(gpa));
     if ( rc != X86EMUL_OKAY )
         return rc;
 
@@ -1953,7 +1956,7 @@ static int nvmx_handle_vmread(struct cpu
     u64 value = 0;
     int rc;
 
-    rc = decode_vmx_inst(regs, &decode, NULL);
+    rc = decode_vmx_inst(regs, &decode, NULL, 0);
     if ( rc != X86EMUL_OKAY )
         return rc;
 
@@ -1996,7 +1999,7 @@ static int nvmx_handle_vmwrite(struct cp
     enum vmx_insn_errno err;
     int rc;
 
-    rc = decode_vmx_inst(regs, &decode, &operand);
+    rc = decode_vmx_inst(regs, &decode, &operand, 0);
     if ( rc != X86EMUL_OKAY )
         return rc;
 
@@ -2038,7 +2041,7 @@ static int nvmx_handle_invept(struct cpu
     unsigned long eptp;
     int ret;
 
-    if ( (ret = decode_vmx_inst(regs, &decode, &eptp)) != X86EMUL_OKAY )
+    if ( (ret = decode_vmx_inst(regs, &decode, &eptp, 16)) != X86EMUL_OKAY )
         return ret;
 
     switch ( reg_read(regs, decode.reg2) )
@@ -2066,7 +2069,7 @@ static int nvmx_handle_invvpid(struct cp
     unsigned long vpid;
     int ret;
 
-    if ( (ret = decode_vmx_inst(regs, &decode, &vpid)) != X86EMUL_OKAY )
+    if ( (ret = decode_vmx_inst(regs, &decode, &vpid, 16)) != X86EMUL_OKAY )
         return ret;
 
     switch ( reg_read(regs, decode.reg2) )