So enabling full hardware-enforced W^X is perhaps a bit to much at
this moment. But enabling the bit that enforces that the kernel
cannot execute pages that are writable by userland should be fine.
The diff does this on all ARMv7 processors that include the
Virtualization Extensions, which is what indicates that this
functionality is supported.
ok?
Index: arch/arm/arm/cpufunc.c
===================================================================
RCS file: /cvs/src/sys/arch/arm/arm/cpufunc.c,v
retrieving revision 1.47
diff -u -p -r1.47 cpufunc.c
--- arch/arm/arm/cpufunc.c 22 Aug 2016 01:41:59 -0000 1.47
+++ arch/arm/arm/cpufunc.c 24 Aug 2016 21:08:50 -0000
@@ -529,6 +529,7 @@ armv7_setup()
{
uint32_t auxctrl, auxctrlmask;
uint32_t cpuctrl, cpuctrlmask;
+ uint32_t id_pfr1;
auxctrl = auxctrlmask = 0;
@@ -568,6 +569,16 @@ armv7_setup()
if (vector_page == ARM_VECTORS_HIGH)
cpuctrl |= CPU_CONTROL_VECRELOC;
+
+ /*
+ * Check for the Virtualization Extensions and enable UWXN of
+ * those are included.
+ */
+ __asm volatile("mrc p15, 0, %0, c0, c1, 1" : "=r"(id_pfr1));
+ if ((id_pfr1 & 0x0000f000) == 0x00001000) {
+ cpuctrlmask |= CPU_CONTROL_UWXN;
+ cpuctrl |= CPU_CONTROL_UWXN;
+ }
/* Clear out the cache */
cpu_idcache_wbinv_all();
Index: arch/arm/include/armreg.h
===================================================================
RCS file: /cvs/src/sys/arch/arm/include/armreg.h,v
retrieving revision 1.36
diff -u -p -r1.36 armreg.h
--- arch/arm/include/armreg.h 24 Aug 2016 13:09:52 -0000 1.36
+++ arch/arm/include/armreg.h 24 Aug 2016 21:08:51 -0000
@@ -248,6 +248,8 @@
#define CPU_CONTROL_L2 (1<<25) /* L2: L2 cache enable */
/* added with v7 */
+#define CPU_CONTROL_WXN (1<<19) /* WXN: Write implies XN */
+#define CPU_CONTROL_UWXN (1<<20) /* UWXN: Unpriv write implies XN */
#define CPU_CONTROL_NMFI (1<<27) /* NMFI: Non Maskable fast interrupt */
#define CPU_CONTROL_TRE (1<<28) /* TRE: TEX Remap Enable */
#define CPU_CONTROL_AFE (1<<29) /* AFE: Access Flag Enable */
