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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 947
916
CASE STUDY 2: WINDOWS 8
CHAP. 11
left to user-mode code that can use the handle on the new process to manipulate its
virtual address space directly.
To support the POSIX subsystem, native process creation has an option to cre-
ate a new process by copying the virtual address space of another process rather
than mapping a section object for a new program. This is used only to implement
fork
for POSIX, and not by Win32. Since POSIX no longer ships with Windows,
process duplication has little use—though sometimes enterprising developers come
up with special uses, similar to uses of
fork
without
exec
in UNIX.
Thread creation passes the CPU context to use for the new thread (which in-
cludes the stack pointer and initial instruction pointer), a template for the TEB, and
a flag saying whether the thread should be immediately run or created in a sus-
pended state (waiting for somebody to call
NtResumeThread
on its handle).
Crea-
tion of the user-mode stack and pushing of the
argv/argc
parameters is left to user-
mode code calling the native NT memory-management APIs on the process hand-
le.
In the Windows Vista release, a new native API for processes,
NtCreateUser-
Process
, was added which moves many of the user-mode steps into the kernel-
mode executive, and combines process creation with creation of the initial thread.
The reason for the change was to support the use of processes as security bound-
aries. Normally, all processes created by a user are considered to be equally trust-
ed. It is the user, as represented by a token, that determines where the trust bound-
ary is.
NtCreateUserProcess
allows processes to also provide trust boundaries, but
this means that the creating process does not have sufficient rights regarding a new
process handle to implement the details of process creation in user mode for proc-
esses that are in a different trust environment. The primary use of a process in a
different trust boundary (called
protected processes
) is to support forms of digital
rights management, which protect copyrighted material from being used improp-
erly.
Of course, protected processes only target user-mode attacks against protect-
ed content and cannot prevent kernel-mode attacks.
Interprocess Communication
Threads can communicate in a wide variety of ways, including pipes, named
pipes, mailslots, sockets, remote procedure calls, and shared files. Pipes have two
modes: byte and message, selected at creation time.
Byte-mode pipes work the
same way as in UNIX.
Message-mode pipes are somewhat similar but preserve
message boundaries, so that four writes of 128 bytes will be read as four 128-byte
messages, and not as one 512-byte message, as might happen with byte-mode
pipes. Named pipes also exist and have the same two modes as regular pipes.
Named pipes can also be used over a network but regular pipes cannot.
Mailslots
are a feature of the now-defunct OS/2 operating system imple-
mented in Windows for compatibility.
They are similar to pipes in some ways, but
not all.
For one thing, they are one way, whereas pipes are two way.
They could
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