svn commit: r338632 - head/sys/dev/xen/privcmd

[Roger Pau Monné]

Author: royger
Date: Thu Sep 13 07:15:02 2018
New Revision: 338632
URL: https://svnweb.freebsd.org/changeset/base/338632

Log:
  xen: temporary disable SMAP when forwarding hypercalls from user-space
  
  The Xen page-table walker used to resolve the virtual addresses in the
  hypercalls will refuse to access user-space pages when SMAP is enabled
  unless the AC flag in EFLAGS is set (just like normal hardware with
  SMAP support would do).
  
  Since privcmd allows forwarding hypercalls (and buffers) from
  user-space into Xen make sure SMAP is temporary disabled for the
  duration of the hypercall from user-space.
  
  Approved by:		re (gjb)
  Sponsored by:		Citrix Systems R&D

Modified:
  head/sys/dev/xen/privcmd/privcmd.c

Modified: head/sys/dev/xen/privcmd/privcmd.c
==============================================================================
--- head/sys/dev/xen/privcmd/privcmd.c	Thu Sep 13 07:14:11 2018	(r338631)
+++ head/sys/dev/xen/privcmd/privcmd.c	Thu Sep 13 07:15:02 2018	(r338632)
@@ -232,9 +232,21 @@ privcmd_ioctl(struct cdev *dev, unsigned long cmd, cad
 		struct ioctl_privcmd_hypercall *hcall;
 
 		hcall = (struct ioctl_privcmd_hypercall *)arg;
-
+#ifdef __amd64__
+		/*
+		 * The hypervisor page table walker will refuse to access
+		 * user-space pages if SMAP is enabled, so temporary disable it
+		 * while performing the hypercall.
+		 */
+		if (cpu_stdext_feature & CPUID_STDEXT_SMAP)
+			stac();
+#endif
 		error = privcmd_hypercall(hcall->op, hcall->arg[0],
 		    hcall->arg[1], hcall->arg[2], hcall->arg[3], hcall->arg[4]);
+#ifdef __amd64__
+		if (cpu_stdext_feature & CPUID_STDEXT_SMAP)
+			clac();
+#endif
 		if (error >= 0) {
 			hcall->retval = error;
 			error = 0;