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

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Message-ID: <lsq.1507553064.265911694@decadent.org.uk>
Date:   Mon, 09 Oct 2017 13:44:24 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Marek Marczykowski-Górecki" 
        <marmarek@...isiblethingslab.com>,
        "Juergen Gross" <jgross@...e.com>
Subject: [PATCH 3.16 084/192] x86/xen: allow userspace access during
 hypercalls

3.16.49-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Marek Marczykowski-Górecki
 <marmarek@...isiblethingslab.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@...isiblethingslab.com>
Reviewed-by: Juergen Gross <jgross@...e.com>
Signed-off-by: Juergen Gross <jgross@...e.com>
[bwh: Backported to 3.16: drop change in HYPERVISOR_dm_op()]
Signed-off-by: Ben Hutchings <ben@...adent.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;
 }