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53 lines
2.1 KiB
Text
53 lines
2.1 KiB
Text
==============================================================
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= =
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= NOTES FROM THE UNDERGROUND =
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= =
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==============================================================
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Below are some of Alex's notes on the mysterious LPC Subsystem
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=========================
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1. Sizes, sizes, sizes...
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=========================
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There are four imporant LPC Sizes to keep in mind. Try to understand them:
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/*
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* This determines the absolute maximum message size (0x100 bytes). For
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* larger values, use a section-backed message.
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*/
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#define PORT_MAXIMUM_MESSAGE_LENGTH 256
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/*
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* This determines the maximum length of an LPC request. It is the largest
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* amount of bytes that an LPC request can take. To calculate this, assume
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* that this is a CONNECTION_REQUEST message, which includes the additionnal
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* LPCP_CONNECTION_MESSAGE structure as well. Therefore, we add the kernel LPC,
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* header, the maximum port size and the size of the connection request
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* structure. This gives a value of 0x15C. However, one must note that NT
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* allocates the Lookaside List using a 16-byte aligned value, making this
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* number 0x160.
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*/
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#define LPCP_MAX_MESSAGE_SIZE ROUND_UP(PORT_MAXIMUM_MESSAGE_LENGTH + \
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sizeof(LPCP_MESSAGE) + \
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sizeof(LPCP_CONNECTION_MESSAGE), 16)
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/*
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* Now, for an actual LPC Request size, we remove the kernel LPC header, which
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* yields the size of the actual LPC Data that follows the Header, making this
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* number 0x148.
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*/
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#define LPC_MAX_MESSAGE_LENGTH (LPCP_MAX_MESSAGE_SIZE - \
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FIELD_OFFSET(LPCP_MESSAGE, Request))
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/*
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* Finally, we'll calculate the maximum size of the Connection Info, giving us
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* 0x104
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*/
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#define LPC_MAX_DATA_LENGTH (LPC_MAX_MESSAGE_LENGTH - \
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sizeof(PORT_MESSAGE) - \
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sizeof(LPCP_CONNECTION_MESSAGE))
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==========================
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2. Structures
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==========================
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SOON. TODO.
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