Windows hotpatching

All that remains to be done is cleanup unlocking the memory etc. Too bad that the technology is so rarely used in practice. Preparing the machine First, we need a proper machine image which can be used for the experiment. NameLength; ImageFileName. MmLoadSystemImage kdg Breakpoint 3 hit nt! MmLoadSystemImage f6acbb68 b2d67 nt! KiFastSystemCallRet bd44 7cc9 ntdll! CodeDescriptors[ Index ]. MappedAddress, Buffer[ Index ] ; if! MiDoCopyMemory f6acbae8 a10 nt! No modifications have yet been done to mrxsmb: kd!

RxpCancelRoutine: fb24 8bff mov edi,edi fb26 55 push ebp fb27 8bec mov ebp,esp Now that looks promising, especially since the fourth column holds the value 5. RxpCancelRoutine: fb24 8bff mov edi,edi No doubt, the first and second row define the two patches necessary to redirect RxpCancelRoutine. Back in MmLockAndCopyMemory, the code referred to by the first to rows look like this: kdu fb1f rdbss! RxpCancelRoutine f6ba kdu fb24 rdbss! When the system initially boots, the Windows loader determines the size of the HPAT area, which is composed of a combination of data and code pages to support ARM64 and scenarios where Retpoline is enabled on x This is handled similarly for user-mode binaries.

When a patch is applied to a base image, the HPAT pages for both the base and the patch images are mapped to valid physical pages.

When a function is patched for the first time, the patch engine allocates an HPAT entry for it and fills the code and data slot with the trampoline code and the target address. Subsequent patches for a function only update the target address. The overwritten opcode is saved in the Undo table to be replaced if the patch is reverted. Figure 3 summarizes this process:. The upcoming Windows Server release includes the following improvements which make hotpatching applicable to a wider set of changes:.

Hotpatch is a powerful feature used by the Azure Fleet and Windows Server Azure Edition to eliminate downtime when applying security patches or even adding small features to the OS.

Although some limitations in the functions being patched still exist for example function signatures can never be changed , most of them has been addressed in the new version of the Engine. Hotpatch-based security updates are available to customers running Windows Server and Windows Server Azure Edition images in the Azure cloud within the automanage framework.

Documentation is provided on this page. We are working on bringing hotpatch-based security updates to a wider set of Windows customers. You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.

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Hotpatching on Windows. Mehmet Iyigun. Published Nov 19 PM Azure Government regions aren't supported in the preview. During the preview phase you can get started in the Azure portal using this link. Once the feature has been registered for your subscription, complete the opt-in process by propagating the change into the Compute resource provider.

Use the Register-AzProviderFeature cmdlet to enable the preview for your subscription. With automatic VM guest patching enabled:. This process kicks off automatically every month when new patches are released.

Patch assessment and installation are automatic, and the process includes rebooting the VM as required. With Hotpatch enabled on supported Windows Server Azure Edition VMs, most monthly security updates are delivered as hotpatches that don't require reboots. Latest Cumulative Updates sent on planned or unplanned baseline months will require VM reboots.

Additional Critical or Security patches may also be available periodically which may require VM reboots. The VM is assessed automatically every few days and multiple times within any day period to determine the applicable patches for that VM. This automatic assessment ensures that any missing patches are discovered at the earliest possible opportunity. Patches are installed within 30 days of the monthly patch releases, following availability-first principles. Patches are installed only during off-peak hours for the VM, depending on the time zone of the VM.

The VM must be running during the off-peak hours for patches to be automatically installed. If a VM is powered off during a periodic assessment, the VM will be assessed and applicable patches will be installed automatically during the next periodic assessment when the VM is powered on.

The next periodic assessment usually happens within a few days. Definition updates and other patches not classified as Critical or Security won't be installed through automatic VM guest patching. On this screen, you'll see the Hotpatch status for your VM.