MFamd64: Add bounds checks on addresses used with /dev/mem.

Reject attempts to read from or memory map offsets in /dev/mem that are
beyond the maximum-supported physical address of the current CPU.

Reviewed by:	kib
MFC after:	1 month
Differential Revision:	https://reviews.freebsd.org/D7408

1 files changed, 14 insertions, 0 deletions

diff --git a/sys/x86/include/x86_var.h b/sys/x86/include/x86_var.h
index 12bc1e07d4c0..92c9f1dafa21 100644
--- a/sys/x86/include/x86_var.h
+++ b/sys/x86/include/x86_var.h
@@ -94,6 +94,20 @@ struct	trapframe;
  */
 typedef void alias_for_inthand_t(void);
 
+/*
+ * Returns the maximum physical address that can be used with the
+ * current system.
+ */
+static __inline vm_paddr_t
+cpu_getmaxphyaddr(void)
+{
+#if defined(__i386__) && !defined(PAE)
+	return (0xffffffff);
+#else
+	return ((1ULL << cpu_maxphyaddr) - 1);
+#endif
+}
+
 void	*alloc_fpusave(int flags);
 void	busdma_swi(void);
 bool	cpu_mwait_usable(void);