[PATCH] x86, kernel: make dump_pagetables a tristate

[Kees Cook <keescook@chromium.org>]

Being able to examine page tables is handy, so make this a module that
can be loaded as needed.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/x86/Kconfig.debug        |    2 +-
 arch/x86/kernel/head.c        |    6 ++++++
 arch/x86/mm/dump_pagetables.c |   13 ++++++++++---
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index c198b7e..a43b7ca 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -70,7 +70,7 @@ config DEBUG_STACKOVERFLOW
 	  If in doubt, say "N".
 
 config X86_PTDUMP
-	bool "Export kernel pagetable layout to userspace via debugfs"
+	tristate "Export kernel pagetable layout to userspace via debugfs"
 	depends on DEBUG_KERNEL
 	select DEBUG_FS
 	---help---
diff --git a/arch/x86/kernel/head.c b/arch/x86/kernel/head.c
index 992f442..871c0ca 100644
--- a/arch/x86/kernel/head.c
+++ b/arch/x86/kernel/head.c
@@ -69,3 +69,9 @@ void __init reserve_ebda_region(void)
 	/* reserve all memory between lowmem and the 1MB mark */
 	memblock_reserve(lowmem, 0x100000 - lowmem);
 }
+
+#ifdef CONFIG_X86_64
+EXPORT_SYMBOL_GPL(init_level4_pgt);
+#else
+EXPORT_SYMBOL_GPL(swapper_pg_dir);
+#endif
diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index 0002a3a..7a54145 100644
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -340,6 +340,8 @@ static int ptdump_open(struct inode *inode, struct file *filp)
 	return single_open(filp, ptdump_show, NULL);
 }
 
+static struct dentry *pe;
+
 static const struct file_operations ptdump_fops = {
 	.open		= ptdump_open,
 	.read		= seq_read,
@@ -347,9 +349,8 @@ static const struct file_operations ptdump_fops = {
 	.release	= single_release,
 };
 
-static int pt_dump_init(void)
+static int __init pt_dump_init(void)
 {
-	struct dentry *pe;
 
 #ifdef CONFIG_X86_32
 	/* Not a compile-time constant on x86-32 */
@@ -369,7 +370,13 @@ static int pt_dump_init(void)
 	return 0;
 }
 
-__initcall(pt_dump_init);
+static void __exit pt_dump_exit(void)
+{
+	debugfs_remove_recursive(pe);
+}
+
+module_init(pt_dump_init);
+module_exit(pt_dump_exit);
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");
 MODULE_DESCRIPTION("Kernel debugging helper that dumps pagetables");
-- 
1.7.9.5


-- 
Kees Cook
Chrome OS Security