ARM: OMAP: Fix SRAM W+X mapping

We are still using custom SRAM code for some SoCs and are not marking
the PM code mapped to SRAM as read-only and executable after we're
done. With CONFIG_DEBUG_WX=y, we will get "Found insecure W+X mapping
at address" warning.

Let's fix this issue the same way as commit 728bbe75 ("misc: sram:
Introduce support code for protect-exec sram type") is doing for
drivers/misc/sram-exec.c.

On omap3, we need to restore SRAM when returning from off mode after
idle, so init time configuration is not enough.

And as we no longer have users for omap_sram_push_address() we can
make it static while at it.

Note that eventually we should be using sram-exec.c for all SoCs.

Cc: stable@vger.kernel.org	# v4.12+
Cc: Dave Gerlach <d-gerlach@ti.com>
Reported-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/plat-omap/include/plat/sram.h

@@ -5,13 +5,4 @@ void omap_map_sram(unsigned long start, unsigned long size,
 			unsigned long skip, int cached);
 void omap_sram_reset(void);
 
-extern void *omap_sram_push_address(unsigned long size);
-
-/* Macro to push a function to the internal SRAM, using the fncpy API */
-#define omap_sram_push(funcp, size) ({				\
-	typeof(&(funcp)) _res = NULL;				\
-	void *_sram_address = omap_sram_push_address(size);	\
-	if (_sram_address)					\
-		_res = fncpy(_sram_address, &(funcp), size);	\
-	_res;							\
-})
+extern void *omap_sram_push(void *funcp, unsigned long size);

arch/arm/plat-omap/sram.c

@@ -23,6 +23,7 @@
 #include <asm/fncpy.h>
 #include <asm/tlb.h>
 #include <asm/cacheflush.h>
+#include <asm/set_memory.h>
 
 #include <asm/mach/map.h>
 
@@ -42,7 +43,7 @@ static void __iomem *omap_sram_ceil;
  * Note that fncpy requires the returned address to be aligned
  * to an 8-byte boundary.
  */
-void *omap_sram_push_address(unsigned long size)
+static void *omap_sram_push_address(unsigned long size)
 {
 	unsigned long available, new_ceil = (unsigned long)omap_sram_ceil;
 
@@ -60,6 +61,30 @@ void *omap_sram_push_address(unsigned long size)
 	return (void *)omap_sram_ceil;
 }
 
+void *omap_sram_push(void *funcp, unsigned long size)
+{
+	void *sram;
+	unsigned long base;
+	int pages;
+	void *dst = NULL;
+
+	sram = omap_sram_push_address(size);
+	if (!sram)
+		return NULL;
+
+	base = (unsigned long)sram & PAGE_MASK;
+	pages = PAGE_ALIGN(size) / PAGE_SIZE;
+
+	set_memory_rw(base, pages);
+
+	dst = fncpy(sram, funcp, size);
+
+	set_memory_ro(base, pages);
+	set_memory_x(base, pages);
+
+	return dst;
+}
+
 /*
  * The SRAM context is lost during off-idle and stack
  * needs to be reset.
@@ -75,6 +100,9 @@ void omap_sram_reset(void)
 void __init omap_map_sram(unsigned long start, unsigned long size,
 				 unsigned long skip, int cached)
 {
+	unsigned long base;
+	int pages;
+
 	if (size == 0)
 		return;
 
@@ -95,4 +123,10 @@ void __init omap_map_sram(unsigned long start, unsigned long size,
 	 */
 	memset_io(omap_sram_base + omap_sram_skip, 0,
 		  omap_sram_size - omap_sram_skip);
+
+	base = (unsigned long)omap_sram_base;
+	pages = PAGE_ALIGN(omap_sram_size) / PAGE_SIZE;
+
+	set_memory_ro(base, pages);
+	set_memory_x(base, pages);
 }