lib: add test module for CONFIG_DEBUG_VIRTUAL

Add a test module that allows testing that CONFIG_DEBUG_VIRTUAL works
correctly, at least that it can catch invalid calls to virt_to_phys()
against the non-linear kernel virtual address map.

Link: http://lkml.kernel.org/r/20170808164035.26725-1-f.fainelli@gmail.com
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -1930,6 +1930,17 @@ config TEST_KMOD
 
 	  If unsure, say N.
 
+config TEST_DEBUG_VIRTUAL
+	tristate "Test CONFIG_DEBUG_VIRTUAL feature"
+	depends on DEBUG_VIRTUAL
+	help
+	  Test the kernel's ability to detect incorrect calls to
+	  virt_to_phys() done against the non-linear part of the
+	  kernel's virtual address map.
+
+	  If unsure, say N.
+
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"

lib/Makefile

@@ -62,6 +62,7 @@ obj-$(CONFIG_TEST_BITMAP) += test_bitmap.o
 obj-$(CONFIG_TEST_UUID) += test_uuid.o
 obj-$(CONFIG_TEST_PARMAN) += test_parman.o
 obj-$(CONFIG_TEST_KMOD) += test_kmod.o
+obj-$(CONFIG_TEST_DEBUG_VIRTUAL) += test_debug_virtual.o
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG

lib/test_debug_virtual.c

@@ -0,0 +1,49 @@
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/export.h>
+#include <linux/mm.h>
+#include <linux/vmalloc.h>
+#include <linux/slab.h>
+#include <linux/sizes.h>
+
+#include <asm/page.h>
+#ifdef CONFIG_MIPS
+#include <asm/bootinfo.h>
+#endif
+
+struct foo {
+	unsigned int bar;
+};
+
+struct foo *foo;
+
+static int __init test_debug_virtual_init(void)
+{
+	phys_addr_t pa;
+	void *va;
+
+	va = (void *)VMALLOC_START;
+	pa = virt_to_phys(va);
+
+	pr_info("PA: %pa for VA: 0x%lx\n", &pa, (unsigned long)va);
+
+	foo = kzalloc(sizeof(*foo), GFP_KERNEL);
+	if (!foo)
+		return -ENOMEM;
+
+	pa = virt_to_phys(foo);
+	va = foo;
+	pr_info("PA: %pa for VA: 0x%lx\n", &pa, (unsigned long)va);
+
+	return 0;
+}
+module_init(test_debug_virtual_init);
+
+static void __exit test_debug_virtual_exit(void)
+{
+	kfree(foo);
+}
+module_exit(test_debug_virtual_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Test module for CONFIG_DEBUG_VIRTUAL");