linux-kernel - [PATCH v2] x86/xen: allow userspace access during hypercalls

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Date:   Mon, 26 Jun 2017 14:49:46 +0200
From:   Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>
To:     xen-devel@...ts.xenproject.org
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, stable@...r.kernel.org
Subject: [PATCH v2] x86/xen: allow userspace access during hypercalls

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.

Cc: stable@...r.kernel.org
Signed-off-by: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>
---
 arch/x86/include/asm/xen/hypercall.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

Changes since v1:
 - add HYPERVISOR_dm_op

diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h
index f6d20f6..32b74a8 100644
--- 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>
@@ -214,10 +215,12 @@ 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;
 }
@@ -476,7 +479,11 @@ static inline int
 HYPERVISOR_dm_op(
 	domid_t dom, unsigned int nr_bufs, void *bufs)
 {
-	return _hypercall3(int, dm_op, dom, nr_bufs, bufs);
+	int ret;
+	stac();
+	ret = _hypercall3(int, dm_op, dom, nr_bufs, bufs);
+	clac();
+	return ret;
 }
 
 static inline void
-- 
2.7.4