linux-kernel - [PATCH] kexec, kernel 2.6.26.5, segmentation fault in kimage_add

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Date:	Tue, 16 Sep 2008 15:18:23 -0400
From:	Jonathan Steel <jon.steel@...ntire.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] kexec, kernel 2.6.26.5, 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.

--- 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@...ntire.com>

Jonathan Steel
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