[PATCH 3.16 084/192] x86/xen: allow userspace access during hypercalls

Ben Hutchings
2017-10-09T13:19:27Z

From: Marek Marczykowski-Górecki
<marmarek@invisiblethingslab.com>

commit c54590cac51db8ab5fd30156bdaba34af915e629 upstream.

Userspace application can do a hypercall through /dev/xen/privcmd, and
some for some hypercalls argument is a pointers to user-provided
structure. When SMAP is supported and enabled, hypervisor can't access.
So, lets allow it.

The same applies to HYPERVISOR_dm_op, where additionally privcmd driver
carefully verify buffer addresses.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
[bwh: Backported to 3.16: drop change in HYPERVISOR_dm_op()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/arch/x86/include/asm/xen/hypercall.h
+++ b/arch/x86/include/asm/xen/hypercall.h
@@ -43,6 +43,7 @@

#include <asm/page.h>
#include <asm/pgtable.h>
+#include <asm/smap.h>

#include <xen/interface/xen.h>
#include <xen/interface/sched.h>
@@ -213,10 +214,12 @@ privcmd_call(unsigned call,
__HYPERCALL_DECLS;
__HYPERCALL_5ARG(a1, a2, a3, a4, a5);

+ stac();
asm volatile("call *%[call]"
: __HYPERCALL_5PARAM
: [call] "a" (&hypercall_page[call])
: __HYPERCALL_CLOBBER5);
+ clac();

return (long)__res;
}