Note: Core Image always works in an RGB colorspace. Data, such as YUV, must first be converted to RGB. Such conversion is at a much higher level than the kernel routine. However, Core Image performs the conversion of YUV texture data automatically for you. Keep in mind that the data provided to your kernel routine by Core Image is always RGB based.
Kernel Detective Full Version
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From the full event tree we can see that it is possible to have visibility over all scenarios, except the kernel compromise through a vulnerable function. This is another reason that kernel compromise stands out as a high risk. In all other scenarios policy enforcement is either working, misconfigured or absent. None of these corrupt the integrity of the kernel, which means that the kernel audit facility will work as intended.
The issue occurred with both CentOS 7.2 and Ubuntu 16.04 kernels, whichused versions 3.10.0-862.11.6 and 4.4.0-130, respectively. However, boththose kernels lagged the most recent kernel, which was 4.19-rc2 at thetime.
Knowing full well that kernel changes may take a while to make it tostable releases, we also added a workaround inGitaly to dealwith this issue. We did experiments to test that calling stat() on thepacked-refs file appears to cause the kernel to revalidate the dentrycache for the renamed file. For simplicity, this is implemented inGitaly regardless of whether the filesystem is NFS; we only do this oncebefore Gitaly "opens" a repository, and there are already other stat()calls that check for other files.
At this point, you might want to double-check your systemd-boot or grub2 config to make sure that it defaults to the correct kernel version.I used systemd-boot so I simply had to modify the default antegros line in /boot/loader/loader.conf to instead read default antegros-lts.
The one last thing that you should probably do is lock the kernel version so that you can be prepared to update the module again when you want to update the kernel.This can be done by simply adding the following line to /etc/pacman.conf:
In this and future labs you will progressively build up your kernel.We will also provide you with some additional source.To fetch that source, use Git to commit your Lab 1 source,fetch the latest version of the course repository,and thencreate a local branch called lab2 based on our lab2branch, origin/lab2:
In the virtual memory layout you are going to set up for JOS in thislab, we will switch from using the x86 segmentation hardware forvirtual memory to using page translation instead. Using pagetranslation, we will accomplish the same virtual memory layout wecurrently use segmentation for, plus much more. While we can'tactually disable the segmentation hardware, we will stop using it foranything interesting, effectively disabling it by giving it segmentswith zero offsets. After you finish this laband the JOS kernel successfully enables paging and "disables"segmentation, the kernel's virtual and linear addresses will be thesame, while its linear and physical addresses will differ because ofpage translation.
It is even possible, though much more difficult,to design the kernel so as not to have to reserve any fixed portionof the processor's linear or virtual address space for itself,but instead effectively to allow allow user-level processesunrestricted use of the entire 4GB of virtual address space -while still fully protecting the kernel from these processesand protecting different processes from each other!
Challenge!Write up an outline of how a kernel could be designedto allow user environments unrestricted useof the full 4GB virtual and linear address space.Hint: the technique is sometimes known as"follow the bouncing kernel."In your design,be sure to address exactly what has to happenwhen the processor transitions between kernel and user modes,and how the kernel would accomplish such transitions.Also describe how the kernelwould access physical memory and I/O devices in this scheme,and how the kernel would accessa user environment's virtual address spaceduring system calls and the like.Finally, think about and describethe advantages and disadvantages of such a schemein terms of flexibility, performance, kernel complexity,and other factors you can think of.
The solution would not just be as simple as just re-enabling SACK. The majority of our hosts were on new-enough kernels that had the SACK Panic patch in place. But we had a few hosts that could not upgrade and were running vulnerable kernel versions. Our solution was to use iptables to block connections with a low MSS value. This block allowed for SACK to be enabled while still blocking the attack.
With a few modifications to the drivers and several small bugfixes to the kernel code the applications started to run. As most of the code you need to add for a new M68K platform is drivers and setup code once things started to work most applications sprang to life. It took a couple of tweaks to get floating point to always behave itself but once done I was able to boot the machine fully multi-user, but without keyboard, mouse or hard disk support.
While any new port is difficult the structure of the Linux M68K kernel tree is very well designed and delivers on its intention to allow easy portability between M68K targets. Several sections of this code are (rightfully) now being used cross architecture as well as cross platform. 2ff7e9595c
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