Memory Protection Unit
ARM DDI 0363G Copyright © 2006-2011 ARM Limited. All rights reserved. 7-5
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Example of using regions that overlap
You can use overlapping regions for stack protection, as shown in Figure 7-2. For example:
• allocate to region 1 the appropriate size for all stacks
• allocate to region 2 the minimum region size, 32 bytes, and position it at the end of the
stack for the current process
• set the region 2 access permissions to No Access.
If the current process overflows the stack it uses, a write access to region 2 by the processor
causes the MPU to raise a permission fault.
Figure 7-2 Overlay for stack protection
Example of using subregions
You can use subregions for stack protection, as shown in Figure 7-3. For example:
• Allocate to region 1 the appropriate size for all stacks.
• Set the least-significant subregion disable bit. That is, set the subregion disable field, bits
[15:8], of the CP15 MPU Region Size Register to
0x01
.
If the current process overflows the stack it uses, a write access by the processor to the disabled
subregion causes the MPU to raise a background fault.
Figure 7-3 Overlapping subregion of memory
0x4000
0x0000
Region 1
Region 2
0x4000
0x0000
Guard region
0x0800
Stack
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