[PATCH] safety check in claim_heap()

[Robert Millan <rmh@aybabtu.com>]

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Hi!

What do you think of adding this kind of checks?  I know it's not a
perfect safegard, but it can save your day in some situations (it helped
me during i386/ieee1275 port, when link address was 0x100000).

-- 
Robert Millan

<GPLv2> I know my rights; I want my phone call!
<DRM> What use is a phone call… if you are unable to speak?
(as seen on /.)

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--- ../../grub2/kern/powerpc/ieee1275/init.c	2008-01-14 15:30:59.000000000 +0100
+++ kern/powerpc/ieee1275/init.c	2008-01-20 15:20:23.000000000 +0100
@@ -143,6 +143,17 @@
         (total + (HEAP_MAX_ADDR - addr) > HEAP_MIN_SIZE))	/* only limit ourselves when we can afford to */
        len = HEAP_MAX_ADDR - addr;
 
+    /* In theory, firmware should already prevent this from happening by not
+       listing our own image in /memory/available.  The check below is intended
+       as a safegard in case that doesn't happen.  It does, however, not protect
+       us from corrupting our module area, which extends up to a
+       yet-undetermined region above _end.  */
+    if ((addr < _end) && ((addr + len) > _start))
+      {
+        grub_printf ("Warning: attempt to claim over our own code!\n");
+        len = 0;
+      }
+
     if (len)
       {
 	/* Claim and use it.  */