[PATCH] kexec, kernel 2.6.26.5, segmentation fault in kimage_add_entry

[Jonathan Steel]

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.

--- linux-2.6.26.5.orig/kernel/kexec.c    2008-09-16 13:17:56.000000000 
-0400
+++ linux-2.6.26.5/kernel/kexec.c    2008-09-16 13:26:35.000000000 -0400
@@ -743,8 +743,15 @@ static struct page *kimage_alloc_page(st
            *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 its
+             * 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;

Signed-off-by: Jonathan Steel <jon.steel@xxxxxxxxxxxx>

Jonathan Steel
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