[hugepage] Check for brk() entering a hugepage region

['David Gibson' <david@gibson.dropbear.id.au>]

Andrew, please apply.  I could have sworn I checked ages ago, and
thought that sys_brk() eventually called do_mmap_pgoff() which would
do the necessary checks.  Can't find any evidence of such a change
though, so either I was just blind at the time, or it happened before
the changeover to git.

Unlike mmap(), the codepath for brk() creates a vma without first
checking that it doesn't touch a region exclusively reserved for
hugepages.  On powerpc, this can allow it to create a normal page vma
in a hugepage region, causing oopses and other badness.

This patch adds a test to prevent this.  With this patch, brk() will
simply fail if it attempts to move the break into a hugepage reserved
region.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Index: working-2.6/mm/mmap.c
===================================================================
--- working-2.6.orig/mm/mmap.c	2006-11-14 14:03:53.000000000 +1100
+++ working-2.6/mm/mmap.c	2006-11-14 14:05:25.000000000 +1100
@@ -1880,6 +1880,10 @@ unsigned long do_brk(unsigned long addr,
 	if ((addr + len) > TASK_SIZE || (addr + len) < addr)
 		return -EINVAL;
 
+	error = is_hugepage_only_range(current->mm, addr, len);
+	if (error)
+		return error;
+
 	flags = VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
 
 	error = arch_mmap_check(addr, len, flags);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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