[Xen-devel] [PATCH v6 04/10] x86: Add support for STAC/CLAC instructions

[Feng Wu <feng.wu@xxxxxxxxx>]

The STAC/CLAC instructions are only available when SMAP feature is
available, but on the other hand they aren't needed if SMAP is not
enabled, or before we start to run userspace, in that case, the
functions and macros do nothing.

Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
 xen/include/asm-x86/asm_defns.h | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/xen/include/asm-x86/asm_defns.h b/xen/include/asm-x86/asm_defns.h
index c4b2bb2..0302836 100644
--- a/xen/include/asm-x86/asm_defns.h
+++ b/xen/include/asm-x86/asm_defns.h
@@ -8,6 +8,8 @@
 #endif
 #include <asm/processor.h>
 #include <asm/percpu.h>
+#include <xen/stringify.h>
+#include <asm/cpufeature.h>
 
 #ifndef __ASSEMBLY__
 void ret_from_intr(void);
@@ -159,6 +161,34 @@ void ret_from_intr(void);
 
 #endif
 
+/* "Raw" instruction opcodes */
+#define __ASM_CLAC      .byte 0x0f,0x01,0xca
+#define __ASM_STAC      .byte 0x0f,0x01,0xcb
+
+#ifdef __ASSEMBLY__
+#define ASM_AC(op)                                       \
+        btl $X86_FEATURE_SMAP & 31,                      \
+        CPUINFO_FEATURE_OFFSET(X86_FEATURE_SMAP)+boot_cpu_data(%rip); \
+        jnc 881f;                                        \
+        __ASM_##op;                                      \
+881:
+
+#define ASM_STAC ASM_AC(STAC)
+#define ASM_CLAC ASM_AC(CLAC)
+#else
+static inline void clac(void)
+{
+    if ( boot_cpu_has(X86_FEATURE_SMAP) )
+        asm volatile (__stringify(__ASM_CLAC) : : : "memory");
+}
+
+static inline void stac(void)
+{
+    if ( boot_cpu_has(X86_FEATURE_SMAP) )
+        asm volatile (__stringify(__ASM_STAC) : : : "memory");
+}
+#endif
+
 #ifdef __ASSEMBLY__
 .macro SAVE_ALL
         addq  $-(UREGS_error_code-UREGS_r15), %rsp
-- 
1.8.3.1


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