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Author: Subject: Kernel memory leaks
marymary100
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[*] Post 510793 posted on 3-1-2018 at 22:59 Reply With Quote
Kernel memory leaks



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It is understood the bug is present in modern Intel processors produced in the past decade. It allows normal user programs – from database applications to JavaScript in web browsers – to discern to some extent the layout or contents of protected kernel memory areas.
The fix is to separate the kernel's memory completely from user processes using what's called Kernel Page Table Isolation, or KPTI. ...
Whenever a running program needs to do anything useful – such as write to a file or open a network connection – it has to temporarily hand control of the processor to the kernel to carry out the job. To make the transition from user mode to kernel mode and back to user mode as fast and efficient as possible, the kernel is present in all processes' virtual memory address spaces, although it is invisible to these programs. When the kernel is needed, the program makes a system call, the processor switches to kernel mode and enters the kernel. When it is done, the CPU is told to switch back to user mode, and reenter the process. While in user mode, the kernel's code and data remains out of sight but present in the process's page tables.
Think of the kernel as God sitting on a cloud, looking down on Earth. It's there, and no normal being can see it, yet they can pray to it.
These KPTI patches move the kernel into a completely separate address space, so it's not just invisible to a running process, it's not even there at all. Really, this shouldn't be needed, but clearly there is a flaw in Intel's silicon that allows kernel access protections to be bypassed in some way.
The downside to this separation is that it is relatively expensive, time wise, to keep switching between two separate address spaces for every system call and for every interrupt from the hardware. These context switches do not happen instantly, and they force the processor to dump cached data and reload information from memory. This increases the kernel's overhead, and slows down the computer.
Your Intel-powered machine will run slower as a result.
...
If you randomize the placing of the kernel's code in memory, exploits can't find the internal gadgets they need to fully compromise a system. The processor flaw could be potentially exploited to figure out where in memory the kernel has positioned its data and code, hence the flurry of software patching.


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LSemmens
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[*] Post 510796 posted on 3-1-2018 at 23:48 Reply With Quote


I wondered why my memory was failing....and here I was, just thinking I was getting old.
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[*] Post 510797 posted on 3-1-2018 at 23:56 Reply With Quote


I am so glad that I still have my Underwood portable typewriter (is there some way that I could fax my replies to Karl's Forums?).

I can't remember every getting a single Critical Update from the manufacturer, AND lo and behold, yes indeed, my spelling (and grammar) was a thousand times better than it is now.

I recall one high school teacher who would not accept a paper with any typos or any erasures.

I somehow missed the introduction of correction fluid [one of the first forms of correction fluid was invented in 1956 by the secretary Bette NesmithGraham, founder of Liquid Paper--it was more commonly referred to as 'white out'].

It was also a certain generation's initial introduction to getting high by sniffing it as the first generation of Liquid Paper contained tolune. Tolune was for many years a common product in factories (as a degreasing agent I think) that some youth that I got to know well used to break into them, steal the stuff, etc.,.

Special education school programs back in that day could only presume that such youth became irrevocably brain damaged--institutionalization of one form or another was out of the question since the costs of such programs were astronomical. I lost touch with them when I moved, and I've often wondered what kinds of adults they turned out to be (if they lived that long).

The embedded pix is exactly the model that I have (AND the factory that it was made in was in my home town-"was" as in long closed down.

JackInCT has attached this image.
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