[PATCH] [16/16] POISON: Add madvise() based injector for poisoned data

[Andi Kleen <andi@firstfloor.org>]

Impact: optional, useful for debugging

Add a new madvice sub command to inject poison for some
pages in a process' address space.  This is useful for
testing the poison page handling.

Open issues:

- This patch allows root to tie up arbitary amounts of memory.
Should this be disabled inside containers?
- There's a small race window between getting the page and injecting.
The patch drops the ref count because otherwise memory_failure
complains about dangling references. In theory with a multi threaded
injector one could inject poison for a process foreign page this way.
Not a serious issue right now.

Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
 include/asm-generic/mman.h |    1 +
 mm/madvise.c               |   37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

Index: linux/mm/madvise.c
===================================================================
--- linux.orig/mm/madvise.c	2009-04-07 16:36:29.000000000 +0200
+++ linux/mm/madvise.c	2009-04-07 16:39:39.000000000 +0200
@@ -208,6 +208,38 @@
 	return error;
 }
 
+#ifdef CONFIG_MEMORY_FAILURE
+/*
+ * Error injection support for memory error handling.
+ */
+static int madvise_poison(unsigned long start, unsigned long end)
+{
+	/*
+	 * RED-PEN
+	 * This allows to tie up arbitary amounts of memory.
+	 * Might be a good idea to disable it inside containers even for root.
+	 */
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	for (; start < end; start += PAGE_SIZE) {
+		struct page *p;
+		int ret = get_user_pages(current, current->mm, start, 1,
+						0, 0, &p, NULL);
+		if (ret != 1)
+			return ret;
+		put_page(p);
+		/*
+ 		 * RED-PEN page can be reused, but otherwise we'll have to fight with the
+		 * refcnt
+		 */
+		printk(KERN_INFO "Injecting memory failure for page %lx at %lx\n",
+		       page_to_pfn(p), start);
+		memory_failure(page_to_pfn(p), 0);
+	}
+	return 0;
+}
+#endif
+
 static long
 madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
 		unsigned long start, unsigned long end, int behavior)
@@ -290,6 +322,11 @@
 	int write;
 	size_t len;
 
+#ifdef CONFIG_MEMORY_FAILURE
+	if (behavior == MADV_POISON)
+		return madvise_poison(start, start+len_in);
+#endif
+
 	write = madvise_need_mmap_write(behavior);
 	if (write)
 		down_write(&current->mm->mmap_sem);
Index: linux/include/asm-generic/mman.h
===================================================================
--- linux.orig/include/asm-generic/mman.h	2009-04-07 16:36:29.000000000 +0200
+++ linux/include/asm-generic/mman.h	2009-04-07 16:39:39.000000000 +0200
@@ -34,6 +34,7 @@
 #define MADV_REMOVE	9		/* remove these pages & resources */
 #define MADV_DONTFORK	10		/* don't inherit across fork */
 #define MADV_DOFORK	11		/* do inherit across fork */
+#define MADV_POISON	12		/* poison the page (root only) */
 
 /* compatibility flags */
 #define MAP_FILE	0

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