Memory-Protection-Constants

The following are the memory-protection options; you must specify one of the following values when allocating or protecting a page in memory. Protection attributes cannot be assigned to a portion of a page; they can only be assigned to a whole page.

Constant/value	Description
PAGE_EXECUTE 0x10	Enables execute access to the committed region of pages. An attempt to write to the committed region results in an access violation. This flag is not supported by the CreateFileMapping function.
PAGE_EXECUTE_READ 0x20	Enables execute or read-only access to the committed region of pages. An attempt to write to the committed region results in an access violation. Windows Server 2003 and Windows XP: This attribute is not supported by the CreateFileMapping function until Windows XP with SP2 and Windows Server 2003 with SP1.
PAGE_EXECUTE_READWRITE 0x40	Enables execute, read-only, or read/write access to the committed region of pages. Windows Server 2003 and Windows XP: This attribute is not supported by the CreateFileMapping function until Windows XP with SP2 and Windows Server 2003 with SP1.
PAGE_EXECUTE_WRITECOPY 0x80	Enables execute, read-only, or copy-on-write access to a mapped view of a file mapping object. An attempt to write to a committed copy-on-write page results in a private copy of the page being made for the process. The private page is marked as PAGE_EXECUTE_READWRITE, and the change is written to the new page. This flag is not supported by the VirtualAlloc or VirtualAllocEx functions. Windows Vista, Windows Server 2003, and Windows XP: This attribute is not supported by the CreateFileMapping function until Windows Vista with SP1 and Windows Server 2008.
PAGE_NOACCESS 0x01	Disables all access to the committed region of pages. An attempt to read from, write to, or execute the committed region results in an access violation. This flag is not supported by the CreateFileMapping function.
PAGE_READONLY 0x02	Enables read-only access to the committed region of pages. An attempt to write to the committed region results in an access violation. If Data Execution Prevention is enabled, an attempt to execute code in the committed region results in an access violation.
PAGE_READWRITE 0x04	Enables read-only or read/write access to the committed region of pages. If Data Execution Prevention is enabled, attempting to execute code in the committed region results in an access violation.
PAGE_WRITECOPY 0x08	Enables read-only or copy-on-write access to a mapped view of a file mapping object. An attempt to write to a committed copy-on-write page results in a private copy of the page being made for the process. The private page is marked as PAGE_READWRITE, and the change is written to the new page. If Data Execution Prevention is enabled, attempting to execute code in the committed region results in an access violation. This flag is not supported by the VirtualAlloc or VirtualAllocEx functions.

The following are modifiers that can be used in addition to the options provided in the previous table, except as noted.

Constant/value	Description
PAGE_GUARD 0x100	Pages in the region become guard pages. Any attempt to access a guard page causes the system to raise a STATUS_GUARD_PAGE_VIOLATION exception and turn off the guard page status. Guard pages thus act as a one-time access alarm. When an access attempt leads the system to turn off guard page status, the underlying page protection takes over. If a guard page exception occurs during a system service, the service typically returns a failure status indicator. This value cannot be used with PAGE_NOACCESS. This flag is not supported by the CreateFileMapping function.
PAGE_NOCACHE 0x200	Sets all pages to be non-cachable. Applications should not use this attribute except when explicitly required for a device. Using the interlocked functions with memory that is mapped with SEC_NOCACHE can result in an EXCEPTION_ILLEGAL_INSTRUCTION exception. The PAGE_NOCACHE flag cannot be used with the PAGE_GUARD, PAGE_NOACCESS, or PAGE_WRITECOMBINE flags. The PAGE_NOCACHE flag can be used only when allocating private memory with the VirtualAlloc, VirtualAllocEx, or VirtualAllocExNuma functions. To enable non-cached memory access for shared memory, specify the SEC_NOCACHE flag when calling the CreateFileMapping function.
PAGE_WRITECOMBINE 0x400	Sets all pages to be write-combined. Applications should not use this attribute except when explicitly required for a device. Using the interlocked functions with memory that is mapped as write-combined can result in an EXCEPTION_ILLEGAL_INSTRUCTION exception. The PAGE_WRITECOMBINE flag cannot be specified with the PAGE_NOACCESS, PAGE_GUARD, and PAGE_NOCACHE flags. The PAGE_WRITECOMBINE flag can be used only when allocating private memory with the VirtualAlloc, VirtualAllocEx, or VirtualAllocExNuma functions. To enable write-combined memory access for shared memory, specify the SEC_WRITECOMBINE flag when calling the CreateFileMapping function. Windows Server 2003 and Windows XP: This flag is not supported until Windows Server 2003 with SP1.