[Xen-devel] [PATCH 8/8] x86/emul: Implement the STAC and CLAC instructions

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Note that unlike most privilege restricted instructions, STAC and CLAC are
documented to raise #UD rather than #GP[0], and indeed do so.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
---
 xen/arch/x86/x86_emulate/x86_emulate.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
b/xen/arch/x86/x86_emulate/x86_emulate.c
index 67495eb..111bb91 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -429,6 +429,7 @@ typedef union {
 #define CR4_OSXMMEXCPT (1<<10)
 #define CR4_UMIP       (1<<11)
 #define CR4_OSXSAVE    (1<<18)
+#define CR4_SMAP       (1<<21)
 
 /* EFLAGS bit definitions. */
 #define EFLG_VIP  (1<<20)
@@ -4362,11 +4363,27 @@ x86_emulate(
 
         switch( modrm )
         {
-#ifdef __XEN__
-        case 0xd1: /* xsetbv */
-        {
             unsigned long cr4;
 
+        case 0xca: /* clac */
+        case 0xcb: /* stac */
+            generate_exception_if(
+                lock_prefix || (_regs.eflags & EFLG_VM), EXC_UD);
+            if ( !ops->read_cr || ops->read_cr(4, &cr4, ctxt) != X86EMUL_OKAY )
+                cr4 = 0;
+            /*
+             * Contrary to expectation (i.e. #GP[0]), #UD for the CPL check is
+             * the documented and observed behaviour.
+             */
+            generate_exception_if(!(cr4 & CR4_SMAP) || !mode_ring0(), EXC_UD);
+
+            _regs.eflags &= ~EFLG_AC;
+            if ( modrm == 0xcb )
+                _regs.eflags |= EFLG_AC;
+            goto no_writeback;
+
+#ifdef __XEN__
+        case 0xd1: /* xsetbv */
             generate_exception_if(vex.pfx, EXC_UD);
             if ( !ops->read_cr || ops->read_cr(4, &cr4, ctxt) != X86EMUL_OKAY )
                 cr4 = 0;
@@ -4376,7 +4393,6 @@ x86_emulate(
                                                 _regs._eax | (_regs.rdx << 
32)),
                                   EXC_GP, 0);
             goto no_writeback;
-        }
 #endif
 
         case 0xd4: /* vmfunc */
-- 
2.1.4


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