[src/trunk]: src/sys/arch Rig the hypercall callback page such that when the ...

[cherry <cherry%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/425ce54be5d6
branches:  trunk
changeset: 448897:425ce54be5d6
user:      cherry <cherry%NetBSD.org@localhost>
date:      Wed Feb 13 05:36:59 2019 +0000

description:
Rig the hypercall callback page such that when the kernel happens to
run without a XEN domain loader having previously overwritten the
hypercall page with its hypercall trampoline machine code, we still
get to detect its presence by calling the xen_version hypercall stub.

We use this hack to detect the presence or absence of the hypervisor,
without relying on the MSR support on HVM domains.

This works as an added sanity check that the hypercall page
registration has indeed succeeded in HVM mode.

diffstat:

 sys/arch/amd64/amd64/locore.S |  14 +++++++++-----
 sys/arch/i386/i386/locore.S   |  27 ++++++++++++++++++++++-----
 2 files changed, 31 insertions(+), 10 deletions(-)

diffs (97 lines):

diff -r 744fe02e40f9 -r 425ce54be5d6 sys/arch/amd64/amd64/locore.S
--- a/sys/arch/amd64/amd64/locore.S     Wed Feb 13 05:28:50 2019 +0000
+++ b/sys/arch/amd64/amd64/locore.S     Wed Feb 13 05:36:59 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: locore.S,v 1.176 2019/02/11 14:59:32 cherry Exp $      */
+/*     $NetBSD: locore.S,v 1.177 2019/02/13 05:36:59 cherry Exp $      */
 
 /*
  * Copyright-o-rama!
@@ -278,6 +278,8 @@
 #define __ASSEMBLY__
 #include <xen/include/public/elfnote.h>
 #include <xen/include/public/xen.h>
+#endif /* XEN */
+
 #ifdef XENPV   
 #define ELFNOTE(name, type, desctype, descdata...) \
 .pushsection .note.name                        ;       \
@@ -312,7 +314,6 @@
        ELFNOTE(Xen, XEN_ELFNOTE_BSD_SYMTAB,     .asciz, "yes")
 #endif
 #endif  /* XENPV */    
-#endif /* XEN */
 
 /*
  * Initialization
@@ -979,9 +980,12 @@
 #if defined(XEN)
 /* space for the hypercall call page */
 #define HYPERCALL_PAGE_OFFSET 0x1000
-.org HYPERCALL_PAGE_OFFSET
-ENTRY(hypercall_page)
-.skip 0x1000
+.align HYPERCALL_PAGE_OFFSET
+ENTRY(hypercall_page) /* Returns -1, on HYPERVISOR_xen_version() */
+.skip  (__HYPERVISOR_xen_version*32), 0x90
+       movq    $-1, %rax
+       retq
+.align HYPERCALL_PAGE_OFFSET, 0x90
 END(hypercall_page)
 #endif /* XEN */
 
diff -r 744fe02e40f9 -r 425ce54be5d6 sys/arch/i386/i386/locore.S
--- a/sys/arch/i386/i386/locore.S       Wed Feb 13 05:28:50 2019 +0000
+++ b/sys/arch/i386/i386/locore.S       Wed Feb 13 05:36:59 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: locore.S,v 1.163 2019/02/11 14:59:32 cherry Exp $      */
+/*     $NetBSD: locore.S,v 1.164 2019/02/13 05:36:59 cherry Exp $      */
 
 /*
  * Copyright-o-rama!
@@ -128,7 +128,7 @@
  */
 
 #include <machine/asm.h>
-__KERNEL_RCSID(0, "$NetBSD: locore.S,v 1.163 2019/02/11 14:59:32 cherry Exp $");
+__KERNEL_RCSID(0, "$NetBSD: locore.S,v 1.164 2019/02/13 05:36:59 cherry Exp $");
 
 #include "opt_copy_symtab.h"
 #include "opt_ddb.h"
@@ -242,6 +242,20 @@
        loop    1b                      ;
 
 
+#ifdef XEN
+/*
+ * Unfortunately, the Xen codebase uses nonstandard preprocessing tools.
+ * See: https://xenbits.xen.org/gitweb/?p=xen.git&a=search&h=HEAD&st=grep&s=__UnDeF__
+ * for a fine selection of examples.
+ *
+ * What this means for us here is that we can't include the standard
+ * xen.h header in assembler code.
+ *
+ * So we have to manually define, and keep track of the values we need, ourselves.
+ */
+#define __HYPERVISOR_xen_version          17
+#endif /* XEN */
+
 #ifdef XENPV
 /*
  * Xen guest identifier and loader selection
@@ -916,9 +930,12 @@
 #if defined(XEN)
 /* space for the hypercall call page */
 #define HYPERCALL_PAGE_OFFSET 0x1000
-.org HYPERCALL_PAGE_OFFSET
-ENTRY(hypercall_page)
-.skip 0x1000
+.align HYPERCALL_PAGE_OFFSET
+ENTRY(hypercall_page) /* Returns -1, on HYPERVISOR_xen_version() */
+.skip  (__HYPERVISOR_xen_version*32), 0x90
+       movl    $-1, %eax
+       retl
+.align HYPERCALL_PAGE_OFFSET, 0x90
 END(hypercall_page)
 
 #ifdef XENPV