powerpc/32s: Use dedicated segment for modules with STRICT_KERNEL_RWX

When STRICT_KERNEL_RWX is set, we want to set NX bit on vmalloc
segments. But modules require exec.

Use a dedicated segment for modules. There is not much space
above kernel, and we don't waste vmalloc space to do alignment.
Therefore, we take the segment before PAGE_OFFSET for modules.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/eb8faba9148b6cf17c696ba776b4e8ee2f6313bf.1593428200.git.christophe.leroy@csgroup.eu

arch/powerpc/Kconfig

@@ -1213,6 +1213,7 @@ config TASK_SIZE_BOOL
 config TASK_SIZE
 	hex "Size of user task space" if TASK_SIZE_BOOL
 	default "0x80000000" if PPC_8xx
+	default "0xb0000000" if PPC_BOOK3S_32 && STRICT_KERNEL_RWX
 	default "0xc0000000"
 endmenu
 

arch/powerpc/include/asm/book3s/32/pgtable.h

@@ -184,24 +184,19 @@ int map_kernel_page(unsigned long va, phys_addr_t pa, pgprot_t prot);
  */
 #define VMALLOC_OFFSET (0x1000000) /* 16M */
 
-/*
- * With CONFIG_STRICT_KERNEL_RWX, kernel segments are set NX. But when modules
- * are used, NX cannot be set on VMALLOC space. So vmalloc VM space and linear
- * memory shall not share segments.
- */
-#if defined(CONFIG_STRICT_KERNEL_RWX) && defined(CONFIG_MODULES)
-#define VMALLOC_START ((ALIGN((long)high_memory, 256L << 20) + VMALLOC_OFFSET) & \
-		       ~(VMALLOC_OFFSET - 1))
-#else
 #define VMALLOC_START ((((long)high_memory + VMALLOC_OFFSET) & ~(VMALLOC_OFFSET-1)))
-#endif
 
 #ifdef CONFIG_KASAN_VMALLOC
 #define VMALLOC_END	ALIGN_DOWN(ioremap_bot, PAGE_SIZE << KASAN_SHADOW_SCALE_SHIFT)
 #else
 #define VMALLOC_END	ioremap_bot
 #endif
 
+#ifdef CONFIG_STRICT_KERNEL_RWX
+#define MODULES_END	ALIGN_DOWN(PAGE_OFFSET, SZ_256M)
+#define MODULES_VADDR	(MODULES_END - SZ_256M)
+#endif
+
 #ifndef __ASSEMBLY__
 #include <linux/sched.h>
 #include <linux/threads.h>

arch/powerpc/mm/ptdump/ptdump.c

@@ -74,6 +74,10 @@ struct addr_marker {
 
 static struct addr_marker address_markers[] = {
 	{ 0,	"Start of kernel VM" },
+#ifdef MODULES_VADDR
+	{ 0,	"modules start" },
+	{ 0,	"modules end" },
+#endif
 	{ 0,	"vmalloc() Area" },
 	{ 0,	"vmalloc() End" },
 #ifdef CONFIG_PPC64
@@ -352,6 +356,10 @@ static void populate_markers(void)
 	address_markers[i++].start_address = PAGE_OFFSET;
 #else
 	address_markers[i++].start_address = TASK_SIZE;
+#endif
+#ifdef MODULES_VADDR
+	address_markers[i++].start_address = MODULES_VADDR;
+	address_markers[i++].start_address = MODULES_END;
 #endif
 	address_markers[i++].start_address = VMALLOC_START;
 	address_markers[i++].start_address = VMALLOC_END;