[PATCH v7 5/5] kasan debug: track pages allocated for vmalloc shadow

[Daniel Axtens <dja@axtens.net>]

Provide the current number of vmalloc shadow pages in
/sys/kernel/debug/kasan_vmalloc/shadow_pages.

Signed-off-by: Daniel Axtens <dja@axtens.net>

---

Merging this is probably overkill, but I leave it to the discretion
of the broader community.

On v4 (no dynamic freeing), I saw the following approximate figures
on my test VM:

 - fresh boot: 720
 - after test_vmalloc: ~14000

With v5 (lazy dynamic freeing):

 - boot: ~490-500
 - running modprobe test_vmalloc pushes the figures up to sometimes
    as high as ~14000, but they drop down to ~560 after the test ends.
    I'm not sure where the extra sixty pages are from, but running the
    test repeately doesn't cause the number to keep growing, so I don't
    think we're leaking.
 - with vmap_stack, spawning tasks pushes the figure up to ~4200, then
    some clearing kicks in and drops it down to previous levels again.
---
 mm/kasan/common.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index e33cbab83309..e40854512417 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -35,6 +35,7 @@
 #include <linux/vmalloc.h>
 #include <linux/bug.h>
 #include <linux/uaccess.h>
+#include <linux/debugfs.h>
 
 #include <asm/tlbflush.h>
 
@@ -750,6 +751,8 @@ core_initcall(kasan_memhotplug_init);
 #endif
 
 #ifdef CONFIG_KASAN_VMALLOC
+static u64 vmalloc_shadow_pages;
+
 static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
 				      void *unused)
 {
@@ -776,6 +779,7 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
 	if (likely(pte_none(*ptep))) {
 		set_pte_at(&init_mm, addr, ptep, pte);
 		page = 0;
+		vmalloc_shadow_pages++;
 	}
 	spin_unlock(&init_mm.page_table_lock);
 	if (page)
@@ -829,6 +833,7 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
 	if (likely(!pte_none(*ptep))) {
 		pte_clear(&init_mm, addr, ptep);
 		free_page(page);
+		vmalloc_shadow_pages--;
 	}
 	spin_unlock(&init_mm.page_table_lock);
 
@@ -947,4 +952,25 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
 				       (unsigned long)shadow_end);
 	}
 }
+
+static __init int kasan_init_vmalloc_debugfs(void)
+{
+	struct dentry *root, *count;
+
+	root = debugfs_create_dir("kasan_vmalloc", NULL);
+	if (IS_ERR(root)) {
+		if (PTR_ERR(root) == -ENODEV)
+			return 0;
+		return PTR_ERR(root);
+	}
+
+	count = debugfs_create_u64("shadow_pages", 0444, root,
+				   &vmalloc_shadow_pages);
+
+	if (IS_ERR(count))
+		return PTR_ERR(root);
+
+	return 0;
+}
+late_initcall(kasan_init_vmalloc_debugfs);
 #endif
-- 
2.20.1