CODEWITHSUNDEEP
linuxkernel
Vi Nguyen
Vi Nguyen

Reputation: 359

What is the function of General Protection?

In linux, when an interrupt or exception occur, if CUrrent Privilege Level (CPL) is lower privilege than Description Privilege Level (DPL).General Protection will be raised! but what is the function of General Protection Fault in this situation? please help me!

Upvotes: 3

Views: 10098

Answers (1)

TOC
TOC

Reputation: 4446

The processor does not permit transfer of execution to an exception or interrupt-handler procedure in a less privileged code segment than the CPL. An attempt to violate this rule results in a general-protection exception (#GP). more on that(http://www.lpthe.jussieu.fr/~talon/pentium3.pdf)

Inside the kernel each exception is handled by a specific exception handler, which usually sends a Unix signal to the process that caused the exception.

In our case : the kernel will generate a signal SIGSEV. The exception handler in this case is general_protection( ) (https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/traps.h)

EDIT : in this link you can get a great explanation about how the kernel compare DPL, CPL and RPL:

http://duartes.org/gustavo/blog/post/cpu-rings-privilege-and-protection

Another good link:

http://www.logix.cz/michal/doc/i386/chp06-03.htm

Upvotes: 14

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