[PATCH 05/20] x86/uaccess/xen: Suppress SMAP warnings

[Peter Zijlstra <peterz@infradead.org>]

drivers/xen/privcmd.o: warning: objtool: privcmd_ioctl()+0x1414: call to hypercall_page() with UACCESS enabled

Xen needs to do HV calls with AC=1 for hysterical raisins. Make the
warning go away.

XXX: arguably we should rename ANNOTATE_NOSPEC_ALTERNATIVE to
     ANNOTATE_IGNORE_ALTERNATIVE.

Cc: andrew.cooper3@citrix.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/include/asm/xen/hypercall.h |   26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

--- a/arch/x86/include/asm/xen/hypercall.h
+++ b/arch/x86/include/asm/xen/hypercall.h
@@ -214,6 +214,24 @@ xen_single_call(unsigned int call,
 	return (long)__res;
 }
 
+static __always_inline void __xen_stac(void)
+{
+	/*
+	 * This is just about as horrible as this interface; we abuse the
+	 * nospec alternative annotation to supress objtool seeing the
+	 * STAC/CLAC and getting confused about it calling random code with
+	 * AC=1.
+	 */
+	asm volatile(ANNOTATE_NOSPEC_ALTERNATIVE
+		     ASM_STAC ::: "memory", "flags");
+}
+
+static __always_inline void __xen_clac(void)
+{
+	asm volatile(ANNOTATE_NOSPEC_ALTERNATIVE
+		     ASM_CLAC ::: "memory", "flags");
+}
+
 static inline long
 privcmd_call(unsigned int call,
 	     unsigned long a1, unsigned long a2,
@@ -222,9 +240,9 @@ privcmd_call(unsigned int call,
 {
 	long res;
 
-	stac();
+	__xen_stac();
 	res = xen_single_call(call, a1, a2, a3, a4, a5);
-	clac();
+	__xen_clac();
 
 	return res;
 }
@@ -430,9 +448,9 @@ HYPERVISOR_dm_op(
 	domid_t dom, unsigned int nr_bufs, struct xen_dm_op_buf *bufs)
 {
 	int ret;
-	stac();
+	__xen_stac();
 	ret = _hypercall3(int, dm_op, dom, nr_bufs, bufs);
-	clac();
+	__xen_clac();
 	return ret;
 }