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101

Memory Protection Unit

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Figure 7-1 Overlapping memory regions

Example of using regions that overlap

You can use overlapping regions for stack protection. 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. 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.

Region 2

Region 1

0x4000

0x0000

0x3000

0x3010

Region 1

0x4000

0x0000

Region 2

1 2 ... 183 184 185 186 187 188 189 190 191 192 193 ... 455 456

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