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Thus, not only does the selected service name determine which newUserClient
logic is triggered, but the type parameter allows additional branching
within that logic. It is commonly used to expose limited or privileged
functionality through different user-client implementations. 
Automating type enumeration through dynamic analysis is often impossible,
as the logic is frequently structured to return the same kernel code for
both valid and invalid types. To ensure we map all possible types, we must
reverse these NewUserClients and verify them by hand.
================
--[ 2.1.5 - External Methods
============================================================================
For each previously identified IOUserClient subclass, we can extract
user-accessible methods by locating either externalMethod or
getTargetAndMethodForIndex. These functions define how the driver
dispatches incoming method calls from user space. To locate them, I use IDA
and search for symbol names like H11ANEInDirectPathClient::externalMethod.
It can also be done in the terminal:
````````````````````````````````````````````````````````````````````````````
ipsw macho info --symbols KEXT_NAME | grep
"externalMethod\|getTargetAndMethodForIndex"
````````````````````````````````````````````````````````````````````````````
Based on the previous example, this would yield:
````````````````````````````````````````````````````````````````````````````
0xfffffe0009a796c0: H11ANEInUserClient::externalMethod(unsigned int,
IOExternalMethodArgumentsOpaque*)
0xfffffe0009a788a0: H11ANEInDirectPathClient::externalMethod(unsigned int,
IOExternalMethodArgumentsOpaque*)
````````````````````````````````````````````````````````````````````````````
As discussed in Part 1, there are several common dispatch patterns, but
ultimately, most of them rely on a method array and a fixed number of
entries. In our case, the decompiled dispatcher looks like this:
````````````````````````````````````````````````````````````````````````````
IOReturn H11ANEInUserClient::externalMethod(
uint32_t selector,
IOExternalMethodArguments *args)
{
return IOUserClient2022::dispatchExternalMethod(
selector,
args,
&H11ANEInUserClient::sMethods,
0x32, // Number of supported methods
this,
nullptr
);
}
````````````````````````````````````````````````````````````````````````````
We're specifically interested in H11ANEInUserClient::sMethods, which is the
method dispatch table. The symbol name for this array may vary, so manual
inspection is required. If you know the symbol name, you can locate it with:
````````````````````````````````````````````````````````````````````````````
ipsw macho info --symbols KEXT_NAME | grep "sMethods"
0xfffffe0007f57b78: __ZN18H11ANEInUserClient8sMethodsE
0xfffffe0007f57a10: __ZN24H11ANEInDirectPathClient8sMethodsE
````````````````````````````````````````````````````````````````````````````
This tells us the dispatch table for H11ANEInUserClient is at
0xfffffe0007f57b78, and it contains 0x32 method entries. To parse the table
correctly, we must know the size of each entry, which depends on the
dispatcher used. After reversing all macOS drivers I found these possible
dispatchers and sizes:
````````````````````````````````````````````````````````````````````````````
IOExternalMethodDispatch2022 == 0x28
IOExternalMethodDispatch == 0x18
getTargetAndMethodForIndex == 0x30
Custom == ???
````````````````````````````````````````````````````````````````````````````
Note that some custom implementations require manual handling. With this
information, we can iterate over the array and identify each method. In
IDA, double-clicking works. In other tools, manually add the entry size to
the base address:
````````````````````````````````````````````````````````````````````````````
Method 0 == 0xfffffe0007f57b78 + 0x28
Method 1 == 0xfffffe0007f57b78 + (0x28 * 2)
...
Method 49 == 0xfffffe0007f57b78 + (0x28 * 0x31)
````````````````````````````````````````````````````````````````````````````
By doing this, we can find the addresses of all functions exposed to user
space for IOConnectCallMethod(), as well as the selectors to use for
calling them. The final question is, what arguments do they expect?
=========
--[ 2.1.6 - Arguments
============================================================================
Even with the correct driver name, service matching, user client type,
and external method selector, calls can still fail due to argument size
validation. Most functions validate sizes to prevent buffer overflows
(though some historically lacked this protection). IOConnectCallMethod()
expects these arguments:
````````````````````````````````````````````````````````````````````````````
kern_return_t IOConnectCallMethod(
mach_port_t connection, // Connection handler from
IOServiceOpen
uint32_t selector, // Method index on user client
const uint64_t *input, // Scalar input parameters array
uint32_t inputCnt, // Number of scalar inputs
const void *inputStruct, // Structured input data buffer