x86/xen: use new hypercall functions instead of hypercall page

commit b1c2cb8 upstream.

Call the Xen hypervisor via the new xen_hypercall_func static-call
instead of the hypercall page.

This is part of XSA-466 / CVE-2024-53241.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Co-developed-by: Peter Zijlstra <peterz@infradead.org>
Co-developed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/include/asm/xen/hypercall.h

@@ -39,9 +39,11 @@
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/pgtable.h>
+#include <linux/instrumentation.h>
 
 #include <trace/events/xen.h>
 
+#include <asm/alternative.h>
 #include <asm/page.h>
 #include <asm/smap.h>
 #include <asm/nospec-branch.h>
@@ -91,9 +93,17 @@ extern struct { char _entry[32]; } hypercall_page[];
 void xen_hypercall_func(void);
 DECLARE_STATIC_CALL(xen_hypercall, xen_hypercall_func);
 
-#define __HYPERCALL		"call hypercall_page+%c[offset]"
-#define __HYPERCALL_ENTRY(x)						\
-	[offset] "i" (__HYPERVISOR_##x * sizeof(hypercall_page[0]))
+#ifdef MODULE
+#define __ADDRESSABLE_xen_hypercall
+#else
+#define __ADDRESSABLE_xen_hypercall __ADDRESSABLE_ASM_STR(__SCK__xen_hypercall)
+#endif
+
+#define __HYPERCALL					\
+	__ADDRESSABLE_xen_hypercall			\
+	"call __SCT__xen_hypercall"
+
+#define __HYPERCALL_ENTRY(x)	"a" (x)
 
 #ifdef CONFIG_X86_32
 #define __HYPERCALL_RETREG	"eax"
@@ -151,7 +161,7 @@ DECLARE_STATIC_CALL(xen_hypercall, xen_hypercall_func);
 	__HYPERCALL_0ARG();						\
 	asm volatile (__HYPERCALL					\
 		      : __HYPERCALL_0PARAM				\
-		      : __HYPERCALL_ENTRY(name)				\
+		      : __HYPERCALL_ENTRY(__HYPERVISOR_ ## name)	\
 		      : __HYPERCALL_CLOBBER0);				\
 	(type)__res;							\
 })
@@ -162,7 +172,7 @@ DECLARE_STATIC_CALL(xen_hypercall, xen_hypercall_func);
 	__HYPERCALL_1ARG(a1);						\
 	asm volatile (__HYPERCALL					\
 		      : __HYPERCALL_1PARAM				\
-		      : __HYPERCALL_ENTRY(name)				\
+		      : __HYPERCALL_ENTRY(__HYPERVISOR_ ## name)	\
 		      : __HYPERCALL_CLOBBER1);				\
 	(type)__res;							\
 })
@@ -173,7 +183,7 @@ DECLARE_STATIC_CALL(xen_hypercall, xen_hypercall_func);
 	__HYPERCALL_2ARG(a1, a2);					\
 	asm volatile (__HYPERCALL					\
 		      : __HYPERCALL_2PARAM				\
-		      : __HYPERCALL_ENTRY(name)				\
+		      : __HYPERCALL_ENTRY(__HYPERVISOR_ ## name)	\
 		      : __HYPERCALL_CLOBBER2);				\
 	(type)__res;							\
 })
@@ -184,7 +194,7 @@ DECLARE_STATIC_CALL(xen_hypercall, xen_hypercall_func);
 	__HYPERCALL_3ARG(a1, a2, a3);					\
 	asm volatile (__HYPERCALL					\
 		      : __HYPERCALL_3PARAM				\
-		      : __HYPERCALL_ENTRY(name)				\
+		      : __HYPERCALL_ENTRY(__HYPERVISOR_ ## name)	\
 		      : __HYPERCALL_CLOBBER3);				\
 	(type)__res;							\
 })
@@ -195,7 +205,7 @@ DECLARE_STATIC_CALL(xen_hypercall, xen_hypercall_func);
 	__HYPERCALL_4ARG(a1, a2, a3, a4);				\
 	asm volatile (__HYPERCALL					\
 		      : __HYPERCALL_4PARAM				\
-		      : __HYPERCALL_ENTRY(name)				\
+		      : __HYPERCALL_ENTRY(__HYPERVISOR_ ## name)	\
 		      : __HYPERCALL_CLOBBER4);				\
 	(type)__res;							\
 })
@@ -209,12 +219,9 @@ xen_single_call(unsigned int call,
 	__HYPERCALL_DECLS;
 	__HYPERCALL_5ARG(a1, a2, a3, a4, a5);
 
-	if (call >= PAGE_SIZE / sizeof(hypercall_page[0]))
-		return -EINVAL;
-
-	asm volatile(CALL_NOSPEC
+	asm volatile(__HYPERCALL
 		     : __HYPERCALL_5PARAM
-		     : [thunk_target] "a" (&hypercall_page[call])
+		     : __HYPERCALL_ENTRY(call)
 		     : __HYPERCALL_CLOBBER5);
 
 	return (long)__res;