Rdmsr windbg for windows

The modern term for the test registers has become msrs, meaning that they may not be present in future designs of the cpu. With rdmsr instruction, you read from the ecx register, and store the. A good solution to solve this problem is using the power and simplicity of python and windbg together. Using windows as guest vm on acrn project acrn v 1. Under linux, we can install the msrtools package, which will allow us to read the devcpuxmsr register values the x is the processor number. If you want to quick install windbg, you can go for older version6. Tech support scams are an industrywide issue where scammers trick you into paying for unnecessary technical support services. Specifically, id probably like to execute the following asm code. Kabirs blogs switching between user mode and kernel mode. However i recall i could read all the 48 processors msr with one command like rdmsr 0x1234 it would recursively read msr 0x1234 on all processors. Also included in the samples download is a windbg extension dll that locates the system service table and displays the system. There is two windbg commands which allow to read and write to a msr, these commands are rdmsr and wrmsr. The windows device driver and file systems experts. Commands from the windbg help learn with flashcards, games, and more for free.

Weve updated windbg to have more modern visuals, faster windows, a fullfledged scripting experience, with the easily extensible debugger data model front and center. Bsod windows 10 crash with blue screen, intel core 2 duo. I am not sure why i would get access errors to this memory. Hooking system calls through msrs infosec resources. If you have a problem with configuring msrs, you have to open your windbg in local kernel debugging mode remember msrs in a vm based kernel debugging might not be true for vmx related options then you can use rdmsr which gives you the corresponding value. How to read msrs from mutiple processors at one time osr.

That will effectively stop the debugged windows operating system and give us a chance to execute windbg commands. Their real base addresses are stored in msrs model specific registers instead of the descriptor table. Getting msrs from windows crash dump reverse engineering. The build process complete without any errors or warnings, but trying to execute pcm.

Windbg is a multipurpose debugger for the microsoft windows computer operating system, distributed by microsoft. Advanced windows memory dump analysis with data structures. Activate the virtualize intel vtx ept, install windows server 2016 tp2 to activate the role of hyperv gui you can install too and install a guest in relation to the hyperv on windows 10 x64. By the way, is there any difference if i use windbg tool windows software. So i jumped to the windbg and tried in a first step to determine how to find the desired msr address and i. Regenerate an iso that includes virtiowin drivers and the windows graphics drivers that were preinstalled from the original windows iso. Checking msrs for x2apic on windows kevin lockes homepage. In this post, i have written a tutorial that goes through the entire process of setting up windbg and configuring symbol lookup for kernelmode debugging with vmware using a. When i was trying to implement this feature in fdbg, a hidden backdoor was discovered, which makes the implementation very easy. Lets first pause the windows execution by clicking on debug break in windbg as shown below.

Reading using windbg the minidump generated upon bsod it seems. That is different modes processor run into on windows os. My first thought was that microsoft used these variables for some purposes. Loading kernel symbols vmm debugging using vmwares gdb. Install and configure windbg for bsod analysis tutorials. Introduction to kernel debugging infosec resources. Backdoor support for controltransfer breakpoint features. Memory access errors in the kernel windbg related discussions kernelmode debugging. Windows system software devs interest list subject. The rdmsr command reads a modelspecific register msr value from the specified address. The latest version of windbg allows debugging of windows 10, windows 8.

I believe, unfortunately, these commands can only be used for live kernel mode debugging. So there are many places when the os switches from user mode to kernel mode or from lower privilege level to high privilege level and vice versa. The third mode tscdeadline mode is an extension that is. Once you do the installation, you can find the program in start menu all programs debugging tools for windows windbg. We can read and write fromto msr registers by using rdmsr and wrmsr. One method for reading the msr values is to use the msr from the abandoned performance inspector project. Using lbr last branch record feature to detect idtshadowingbased malicious idt hooking thanks to yushi who shared a presentation eli. Windows software development kit sdk windows driver kit wdk windbg training courses. Normal breakpoints bp in windbg, can only be set if the debugger is. Vmcsauditor a bochsbased hypervisor layout checker. Long story, short, i got the values from the msrs, and it it looks like rw was crashing whenever i tried to get it to read a nonexistent msr. In long mode, segmentation is not really used and all segment registers have base of 0.

Original debugging was done with windbg, with breakpoints on known instances of the cpuid instruction within the nvidia driver. Download windbg for windows 7, windows 8, xp, server 2008. The vertarget command displays the current version of the microsoft windows operating system of the target computer. Kd and kernelmode windbg support multiple processor debugging. Backdoor support for controltransfer breakpoint features in. Baremetal performance for io virtualization with me. Memory access errors in the kernel posted by robert kuster 06 may 2010. The first 2 modes periodic and oneshot are supported by all local apics. System call optimization with the sysenter instruction. The presence of msrs on your processor is indicated by cpuid.

Windows operating system and give us a chance to execute windbg. For instance, we need to get msr 0x481 then execute the following command in windbg. It is well known that both amd64 and intel em64t cpus support controltransfer breakpoint features. To get started with windows debugging, see getting started with windows debugging. The windbg extension command to view process information is. Practical foundations of windows debugging, disassembling, reversing. We can read and write into those registers by using the rdmsr and wrmsr instructions, which are privileged instructions and therefore must be executed by the operating system. Newest windbg questions reverse engineering stack exchange. Instead i installed the windows driver kit which included windbg, which has the ability to perform a live kernel debug, which gives me the rdmsr command.

Whether x2apic is enabled or disabled is both a matter of hardwarebiosdriver support and a matter of policy. Windows developersnamely, the windows debuggers windbg and. There is two windbg commands which allow to read and write to a. Each msr that is accessed by the rdmsr and wrmsr group of instructions is identified by a 32bit integer. As discussed at com7opf4257kerneldumprdmsr, msrs arent saved in crashdumps. Ntdev is sponsored by osr for our schedule of wdf, wdm, debugging and other seminars visit. You can perform this kind of debugging on any multiprocessor platform. Newest windbg questions feed subscribe to rss newest windbg questions feed to subscribe to this rss feed, copy and paste this url into your. Multiprocessor syntax windows drivers microsoft docs. The rdmsr command can display msrs on x86based, itaniumbased, and x64based platforms. Im analyzing a crash dump bsod on a windows box where i suspect some malware is doing something with the msrs but it doesnt look like any of them are available via the wrmsr and rdmsr commands. I need to read msr 176h to find out if ther is a hook at syscall. Once we break into the system, we will be able to input windbg commands at the kd shell as seen on the picture below.

Using lbr last branch record feature to detect idt. Since the rdmsr instruction must be executed at privilege level 0, a kernelmode driver must be used. Debugging with registers part 3 machines can think. In that hypervisor eli, it innovates an idea of gust idt shadow or idt virtualization design for. Ive used two separate dump files, so it will appear as two. Can i read state of msr regsiters when im analyzing memory dump. The wrmsr command writes a value to a modelspecific register msr at the specified address. Windows internals, system security, theoretical computer science and debugging. I am running windbg on windows 7 64 as an administrator, and it is connecting to a vmware windows xp 32bit system. Lastexceptionfromip fffff8000104167f rdmsr fffff80001041681 mov. Newer platforms, such as windows xp and 2003, normally use another method to call system services. For the study was used the vmware workstation 12, windbg 10, ida pro and different versions of windows.