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

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

['David Gibson']

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

[Adam Litke]

On Tue, 2006-11-14 at 15:03 +1100, 'David Gibson' wrote:
> 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>
Acked-by: Adam Litke <agl@us.ibm.com>

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

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

[Bill Irwin]

On Tue, Nov 14, 2006 at 03:03:39PM +1100, 'David Gibson' wrote:
> 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>

Acked-by: William Irwin <wli@holomorphy.com>


-- wli

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