generic debug pagealloc

CONFIG_DEBUG_PAGEALLOC is now supported by x86, powerpc, sparc64, and
s390.  This patch implements it for the rest of the architectures by
filling the pages with poison byte patterns after free_pages() and
verifying the poison patterns before alloc_pages().

This generic one cannot detect invalid page accesses immediately but
invalid read access may cause invalid dereference by poisoned memory and
invalid write access can be detected after a long delay.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 129 insertions, 0 deletions

diff --git a/mm/debug-pagealloc.c b/mm/debug-pagealloc.c
new file mode 100644
index 000000000000..a1e3324de2b5
--- /dev/null
+++ b/mm/debug-pagealloc.c
@@ -0,0 +1,129 @@
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/page-debug-flags.h>
+#include <linux/poison.h>
+
+static inline void set_page_poison(struct page *page)
+{
+        __set_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);
+}
+
+static inline void clear_page_poison(struct page *page)
+{
+        __clear_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);
+}
+
+static inline bool page_poison(struct page *page)
+{
+        return test_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);
+}
+
+static void poison_highpage(struct page *page)
+{
+        /*
+         * Page poisoning for highmem pages is not implemented.
+         *
+         * This can be called from interrupt contexts.
+         * So we need to create a new kmap_atomic slot for this
+         * application and it will need interrupt protection.
+         */
+}
+
+static void poison_page(struct page *page)
+{
+        void *addr;
+
+        if (PageHighMem(page)) {
+                poison_highpage(page);
+                return;
+        }
+        set_page_poison(page);
+        addr = page_address(page);
+        memset(addr, PAGE_POISON, PAGE_SIZE);
+}
+
+static void poison_pages(struct page *page, int n)
+{
+        int i;
+
+        for (i = 0; i < n; i++)
+                poison_page(page + i);
+}
+
+static bool single_bit_flip(unsigned char a, unsigned char b)
+{
+        unsigned char error = a ^ b;
+
+        return error && !(error & (error - 1));
+}
+
+static void check_poison_mem(unsigned char *mem, size_t bytes)
+{
+        unsigned char *start;
+        unsigned char *end;
+
+        for (start = mem; start < mem + bytes; start++) {
+                if (*start != PAGE_POISON)
+                        break;
+        }
+        if (start == mem + bytes)
+                return;
+
+        for (end = mem + bytes - 1; end > start; end--) {
+                if (*end != PAGE_POISON)
+                        break;
+        }
+
+        if (!printk_ratelimit())
+                return;
+        else if (start == end && single_bit_flip(*start, PAGE_POISON))
+                printk(KERN_ERR "pagealloc: single bit error\n");
+        else
+                printk(KERN_ERR "pagealloc: memory corruption\n");
+
+        print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
+                        end - start + 1, 1);
+        dump_stack();
+}
+
+static void unpoison_highpage(struct page *page)
+{
+        /*
+         * See comment in poison_highpage().
+         * Highmem pages should not be poisoned for now
+         */
+        BUG_ON(page_poison(page));
+}
+
+static void unpoison_page(struct page *page)
+{
+        if (PageHighMem(page)) {
+                unpoison_highpage(page);
+                return;
+        }
+        if (page_poison(page)) {
+                void *addr = page_address(page);
+
+                check_poison_mem(addr, PAGE_SIZE);
+                clear_page_poison(page);
+        }
+}
+
+static void unpoison_pages(struct page *page, int n)
+{
+        int i;
+
+        for (i = 0; i < n; i++)
+                unpoison_page(page + i);
+}
+
+void kernel_map_pages(struct page *page, int numpages, int enable)
+{
+        if (!debug_pagealloc_enabled)
+                return;
+
+        if (enable)
+                unpoison_pages(page, numpages);
+        else
+                poison_pages(page, numpages);
+}