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== sceKernelLoadExec buffer overflow by hitchhikr / Neural: PSP 2.01-2.60 ==
== sceKernelLoadExec buffer overflow by hitchhikr / Neural: PSP 2.01-2.60 ==


There is a subroutine in loadexec.prx that takes a path as an argument. It looks for the character ":" in that path, and calculates the length of the drive name from that (e.g. "ms0:"). It then copies the drive name onto the stack with strncpy.
There was one subroutine that took a path as an argument. It looked for the character ":" in that path, and calculated the length of the drive name from that (e.g. "ms0:"). It then copied the drive name onto the stack with strncpy.
 
The exploit is located in a subroutine in the loadexec.prx file. It is at address 0x88064C94 (game mode) in System Software version 2.60. The purpose of this procedure (used in other functions like "sceKernelLoadExec") is to check that the drive part of a filename is valid and legit. It allocates 48 bytes of stack and the return address to the calling function is stored at the end of it (from 44th to 47th bytes). It starts by checking the first char of the string to see if it is an empty drive name, if it is not the routine extracts the part of the filename that contain the drive name and copies it into the allocated stack. It only stops when it encounters a ':' char. Since it does not check any string length during the copy, if the drive name supplied by user is big enough, then it will overwrite the rest of the stack based values, like the return address for example. Hence why a drive name of 48 chars (+ an extra ':' char to let the loop ends) containing an address to an arbitrary position in memory (pointing to a function of ours for example) located from the 44th to 47th chars in the filename will allow us to run any code we want in the context of the executing routine (kernel mode) as when it ends, it reloads the return address from the stack and directly jumps to it.


In later System Software versions, loadexec checks if the drive name is longer than 0x1F bytes. If it is, it returns an error. Look at sub_21E0 in 6.60 loadexec_01g.prx.
In later System Software versions, loadexec checks if the drive name is longer than 0x1F bytes. If it is, it returns an error. Look at sub_21E0 in 6.60 loadexec_01g.prx.
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