[Xen-devel] [PATCH v2] 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>

v2:
 * Exclude the use of legacy prefixes.  Their exclusion is undocumented but
   consistent with observed behaviour and the other Grp7 instructions.
 * Drop the %cr4 check.  Introduce a CPUID check instead.
---
 xen/arch/x86/x86_emulate/x86_emulate.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
b/xen/arch/x86/x86_emulate/x86_emulate.c
index fe055cf..dfb6f47 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -433,6 +433,7 @@ 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_ID   (1<<21)
@@ -1295,6 +1296,7 @@ static bool vcpu_has(
 #define vcpu_has_bmi1()        vcpu_has(         7, EBX,  3, ctxt, ops)
 #define vcpu_has_hle()         vcpu_has(         7, EBX,  4, ctxt, ops)
 #define vcpu_has_rtm()         vcpu_has(         7, EBX, 11, ctxt, ops)
+#define vcpu_has_smap()        vcpu_has(         7, EBX, 20, ctxt, ops)
 
 #define vcpu_must_have(feat) \
     generate_exception_if(!vcpu_has_##feat(), EXC_UD)
@@ -4354,6 +4356,18 @@ x86_emulate(
 
         switch( modrm )
         {
+        case 0xca: /* clac */
+        case 0xcb: /* stac */
+            vcpu_must_have(smap);
+            generate_exception_if(
+                lock_prefix || vex.pfx ||
+                (_regs.eflags & EFLG_VM) || !mode_ring0(), EXC_UD);
+
+            _regs.eflags &= ~EFLG_AC;
+            if ( modrm == 0xcb )
+                _regs.eflags |= EFLG_AC;
+            goto no_writeback;
+
 #ifdef __XEN__
         case 0xd1: /* xsetbv */
         {
-- 
2.1.4


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