kexec: fix segmentation fault in kimage_add_entry

A segmentation fault can occur in kimage_add_entry in kexec.c when loading
a kernel image into memory.  The fault occurs because a page is requested
by calling kimage_alloc_page with gfp_mask GFP_KERNEL and the function may
actually return a page with gfp_mask GFP_HIGHUSER.  The high mem page is
returned because it was swapped with the kernel page due to the kernel
page being a page that will shortly be copied to.

This patch ensures that kimage_alloc_page returns a page that was created
with the correct gfp flags.

I have verified the change and fixed the whitespace damage of the original
patch.  Jonathan did a great job of tracking this down after he hit the
problem.  -- Eric

Signed-off-by: Jonathan Steel <jon.steel@esentire.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/kernel/kexec.c b/kernel/kexec.c
index 59f3f0df35d4..aef265325cd3 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -753,8 +753,14 @@ static struct page *kimage_alloc_page(struct kimage *image,
                         *old = addr | (*old & ~PAGE_MASK);
 
                         /* The old page I have found cannot be a
-                         * destination page, so return it.
+                         * destination page, so return it if it's
+                         * gfp_flags honor the ones passed in.
                          */
+                        if (!(gfp_mask & __GFP_HIGHMEM) &&
+                            PageHighMem(old_page)) {
+                                kimage_free_pages(old_page);
+                                continue;
+                        }
                         addr = old_addr;
                         page = old_page;
                         break;