Manualsbrain.com
  1. Manuals
  2. Brands
  3. Intel
  4. architecture ia-32
  5. User Manual

Intel architecture ia-32 User Manual

Download
Page of 636
4-40 Vol. 3A
PROTECTION
Page-level protection can be used to enhance segment-level protection. For example, if a large
read-write data segment is paged, the page-protection mechanism can be used to write-protect
individual pages.
NOTE:
* If CR0.WP = 1, access type is determined by the R/W flags of the page-directory and page-table entries.
IF CR0.WP = 0, supervisor privilege permits read-write access.
4.13
PAGE-LEVEL PROTECTION AND EXECUTE-DISABLE BIT
In addition to page-level protection offered by the U/S and R/W flags, enhanced PAE-enabled
paging structures (see Section 3.10.3, “Enhanced Paging Data Structures”) provide the execute-
disable bit. This bit offers additional protection for data pages. 
An IA-32 processor with the execute disable bit capability can prevent data pages from being
used by malicious software to execute code. This capability is provided in:
•
32-bit protected mode with PAE enabled.
•
IA-32e mode.
Table 4-3.  Combined Page-Directory and Page-Table Protection
Page-Directory Entry
Page-Table Entry
Combined Effect
Privilege
Access Type
Privilege
Access Type 
Privilege 
Access Type
User 
Read-Only User
Read-Only User 
Read-Only
User
Read-Only User 
Read-Write
User
Read-Only
User
Read-Write
User
Read-Only
User
Read-Only 
User
Read-Write
User
Read-Write
User
Read/Write
User
Read-Only
Supervisor
Read-Only
Supervisor
Read/Write*
User
Read-Only
Supervisor
Read-Write
Supervisor
Read/Write*
User
Read-Write
Supervisor
Read-Only Supervisor
Read/Write*
User Read-Write
Supervisor
Read-Write
Supervisor 
Read/Write
Supervisor
Read-Only
User
Read-Only
Supervisor
Read/Write*
Supervisor
Read-Only
User
Read-Write
Supervisor
Read/Write*
Supervisor
Read-Write
User
Read-Only
Supervisor
Read/Write*
Supervisor
Read-Write
User
Read-Write
Supervisor
Read/Write
Supervisor
Read-Only
Supervisor
Read-Only
Supervisor
Read/Write*
Supervisor
Read-Only
Supervisor
Read-Write
Supervisor
Read/Write*
Supervisor
Read-Write
Supervisor
Read-Only
Supervisor
Read/Write*
Supervisor
Read-Write
Supervisor
Read-Write
Supervisor
Read/Write