kexec: add restriction on kexec_load() segment sizes

I hit the following issue when run trinity in my system.  The kernel is
3.4 version, but mainline has the same issue.

The root cause is that the segment size is too large so the kerenl
spends too long trying to allocate a page.  Other cases will block until
the test case quits.  Also, OOM conditions will occur.

Call Trace:
  __alloc_pages_nodemask+0x14c/0x8f0
  alloc_pages_current+0xaf/0x120
  kimage_alloc_pages+0x10/0x60
  kimage_alloc_control_pages+0x5d/0x270
  machine_kexec_prepare+0xe5/0x6c0
  ? kimage_free_page_list+0x52/0x70
  sys_kexec_load+0x141/0x600
  ? vfs_write+0x100/0x180
  system_call_fastpath+0x16/0x1b

The patch changes sanity_check_segment_list() to verify that the usage by
all segments does not exceed half of memory.

[[email protected]: fix for kexec-return-error-number-directly.patch, update comment]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: zhong jiang <[email protected]>
Suggested-by: Eric W. Biederman <[email protected]>
Cc: Vivek Goyal <[email protected]>
Cc: Dave Young <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/kexec_core.c

@@ -146,6 +146,7 @@ EXPORT_SYMBOL_GPL(kexec_crash_loaded);
  * allocating pages whose destination address we do not care about.
  */
 #define KIMAGE_NO_DEST (-1UL)
+#define PAGE_COUNT(x) (((x) + PAGE_SIZE - 1) >> PAGE_SHIFT)
 
 static struct page *kimage_alloc_page(struct kimage *image,
 				       gfp_t gfp_mask,
@@ -155,6 +156,7 @@ int sanity_check_segment_list(struct kimage *image)
 {
 	int i;
 	unsigned long nr_segments = image->nr_segments;
+	unsigned long total_pages = 0;
 
 	/*
 	 * Verify we have good destination addresses.  The caller is
@@ -214,6 +216,21 @@ int sanity_check_segment_list(struct kimage *image)
 			return -EINVAL;
 	}
 
+	/*
+	 * Verify that no more than half of memory will be consumed. If the
+	 * request from userspace is too large, a large amount of time will be
+	 * wasted allocating pages, which can cause a soft lockup.
+	 */
+	for (i = 0; i < nr_segments; i++) {
+		if (PAGE_COUNT(image->segment[i].memsz) > totalram_pages / 2)
+			return -EINVAL;
+
+		total_pages += PAGE_COUNT(image->segment[i].memsz);
+	}
+
+	if (total_pages > totalram_pages / 2)
+		return -EINVAL;
+
 	/*
 	 * Verify we have good destination addresses.  Normally
 	 * the caller is responsible for making certain we don't