We can see that the program above does exactly what we want it to do. When we run the program, the Windbg will catch it as presented on the picture below. This code is presented on the picture below:.
Since the sysenter instruction is located at the address 0x7C90E, we can set a breakpoint at that address as follows:. After that, we can use the g command to run the program until the breakpoint is hit. At that point, we can use the rdmsr command to display the values of the machine specific registers MSR. At this point, we must be aware of the fact that , and MSR registers are used to transfer control to kernel mode.
If we set a breakpoint on that location and execute the t command, we can see that the breakpoint is immediately hit. We can see that both 0x2e interrupt as well as the sysenter instruction led to the same point in the kernel mode, which means that they are really used for the same thing, but the actual procedure of doing it is a little different. A new tab for your requested boot camp pricing will open in 5 seconds.
If it doesn't open, click here. He is very interested in finding new bugs in real world software products with source code analysis, fuzzing and reverse engineering. He also has a great passion for developing his own simple scripts for security related problems and learning about new hacking techniques. He knows a great deal about programming languages, as he can write in couple of dozen of them.
His passion is also Antivirus bypassing techniques, malware research and operating systems, mainly Linux, Windows and BSD. Your email address will not be published. Posted: March 29, We've encountered a new and totally unexpected error. Get instant boot camp pricing.
Thank you! In this Series. The initial base address value of the IDTR after the processor is powered up or reset is 0. Instruction ordering. Instructions following an INT n may be fetched from memory before earlier instructions complete execution, but they will not execute even speculatively until all instructions prior to the INT n have completed execution the later instructions may execute before data stored by the earlier instructions have become globally visible. If the instruction pointer in the IDT or in the interrupt, trap, or task gate is beyond the code segment limits.
If an interrupt, trap, or task gate, code segment, or TSS segment selector index is outside its descriptor table limits. If the segment selector in an interrupt or trap gate does not point to a segment descriptor for a code segment.
If pushing the return address, flags, or error code onto the stack exceeds the bounds of the stack segment and no stack switch occurs. If pushing the return address, flags, error code, or stack segment pointer exceeds the bounds of the new stack segment when a stack switch occurs.
If DPL of the stack segment descriptor pointed to by the stack segment selector in the TSS is not equal to the DPL of the code segment descriptor for the interrupt or trap gate.
If pushing the return address, flags, or error code onto the stack exceeds the bounds of the stack segment. This is quite unlike a hardware interrupt, which occurs at the hardware level. A software interrupt only communicates with the kernel and indirectly interrupts the central processing unit. All software interrupts are associated with an interrupt handler, which is actually just a routine that is activated when an interrupt happens. Only one bit of information is communicated during a software interrupt.
This request, in turn, calls kernel routines that actually perform the service. A software interrupt often emulates most of the features of a hardware interrupt. Like a hardware interrupt, it calls only a specific interrupt vector and saves the accumulators and registers.
A software interrupt can also make use of some of the hardware interrupt routines. Similar in functionality to a subroutine call, a software interrupt is used for different purposes in a device. One notable example is when communicating with the disk controller for reading and writing data to and from a disk.
By: Brad Rudisail Contributor.
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