[Xen-changelog] [xen stable-4.6] x86emul: fix rIP handling

[patchbot@xxxxxxx]

commit 54ea2be5ecf517e379e9287472d84f8de24f867d
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Mar 4 13:03:16 2016 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Mar 4 13:03:16 2016 +0100

    x86emul: fix rIP handling
    
    Deal with rIP just like with any other register: Truncate to designated
    width upon entry, write back the zero-extended 32-bit value when
    emulating 32-bit code, and leave the upper 48 bits unchanged for 16-bit
    code.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 0640ffb67fb92e2561c63b9308c27b71281fdd72
    master date: 2016-02-18 15:05:34 +0100
---
 xen/arch/x86/x86_emulate/x86_emulate.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
b/xen/arch/x86/x86_emulate/x86_emulate.c
index 56aef3e..5fb0f7f 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -570,7 +570,6 @@ do{ asm volatile (                                          
            \
 /* Fetch next part of the instruction being emulated. */
 #define insn_fetch_bytes(_size)                                         \
 ({ unsigned long _x = 0, _eip = _regs.eip;                              \
-   if ( !mode_64bit() ) _eip = (uint32_t)_eip; /* ignore upper dword */ \
    _regs.eip += (_size); /* real hardware doesn't truncate */           \
    generate_exception_if((uint8_t)(_regs.eip -                          \
                                    ctxt->regs->eip) > MAX_INST_LEN,     \
@@ -1491,6 +1490,10 @@ x86_emulate(
 #endif
     }
 
+    /* Truncate rIP to def_ad_bytes (2 or 4) if necessary. */
+    if ( def_ad_bytes < sizeof(_regs.eip) )
+        _regs.eip &= (1UL << (def_ad_bytes * 8)) - 1;
+
     /* Prefix bytes. */
     for ( ; ; )
     {
@@ -3803,6 +3806,21 @@ x86_emulate(
 
     /* Commit shadow register state. */
     _regs.eflags &= ~EFLG_RF;
+    switch ( __builtin_expect(def_ad_bytes, sizeof(_regs.eip)) )
+    {
+        uint16_t ip;
+
+    case 2:
+        ip = _regs.eip;
+        _regs.eip = ctxt->regs->eip;
+        *(uint16_t *)&_regs.eip = ip;
+        break;
+#ifdef __x86_64__
+    case 4:
+        _regs.rip = _regs._eip;
+        break;
+#endif
+    }
     *ctxt->regs = _regs;
 
  done:
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.6

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