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29 September 1997 – Subject To Change
Security Holes
Security holes exist when unprivileged software (that is, software that is running out-
side of kernel mode) can:
•
Affect the operation of another process without authorization from the operating
system.
•
Amplify its privilege without authorization from the operating system.
•
Communicate with another process, either overtly or covertly, without authori-
zation from the operating system.
Signal Names
Signal names are printed in lowercase, boldface type. Low-asserted signals are indi-
cated by the _l suffix, while high-asserted signals have the _h suffix. For example,
osc_clk_in_h is a high-asserted signal, and osc_clk_in_l is a low-asserted signal.
Unpredictable and Undefined
Throughout this manual, the terms UNPREDICTABLE and UNDEFINED are used.
Their meanings are quite different and must be carefully distinguished.
In particular, only privileged software (that is, software running in kernel mode) can
trigger UNDEFINED operations. Unprivileged software cannot trigger UNDE-
FINED operations. However, either privileged or unprivileged software can trigger
UNPREDICTABLE results or occurrences.
UNPREDICTABLE results or occurrences do not disrupt the basic operation of the
processor. The processor continues to execute instructions in its normal manner. In
contrast, UNDEFINED operations can halt the processor or cause it to lose informa-
tion.
The terms UNPREDICTABLE and UNDEFINED can be further described as fol-
lows:
Unpredictable
•
Results or occurrences specified as UNPREDICTABLE may vary from moment
to moment, implementation to implementation, and instruction to instruction
within implementations. Software can never depend on results specified as
UNPREDICTABLE.