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https://git.kernel.org/…/ke…/... sure some of you are working on the patches already, if you are then lets connect cause, I am an ardent researcher for the same as of now.
So here it goes:
As soon as kernel page table isolation(KPTI) bug will be out of embargo, Whatsapp and FB will be flooded with over-night kernel "shikhuritee" experts who will share shitty advices non-stop.
1. The bug under embargo is a side channel attack, which exploits the fact that Intel chips come with speculative execution without proper isolation between user pages and kernel pages. Therefore, with careful scheduling and timing attack will reveal some information from kernel pages, while the code is running in user mode.
In easy terms, if you have a VPS, another person with VPS on same physical server may read memory being used by your VPS, which will result in unwanted data leakage. To make the matter worse, a malicious JS from innocent looking webpage might be (might be, because JS does not provide language constructs for such fine grained control; atleast none that I know as of now) able to read kernel pages, and pawn you real hard, real bad.
2. The bug comes from too much reliance on Tomasulo's algorithm for out-of-order instruction scheduling. It is not yet clear whether the bug can be fixed with a microcode update (and if not, Intel has to fix this in silicon itself). As far as I can dig, there is nothing that hints that this bug is fixable in microcode, which makes the matter much worse. Also according to my understanding a microcode update will be too trivial to fix this kind of a hardware bug.
3. A software-only remedy is possible, and that is being implemented by all major OSs (including our lovely Linux) in kernel space. The patch forces Translation Lookaside Buffer to flush if a context switch happens during a syscall (this is what I understand as of now). The benchmarks are suggesting that slowdown will be somewhere between 5%(best case)-30%(worst case).
4. Regarding point 3, syscalls don't matter much. Only thing that matters is how many times syscalls are called. For example, if you are using read() or write() on 8MB buffers, you won't have too much slowdown; but if you are calling same syscalls once per byte, a heavy performance penalty is guaranteed. All processes are which are I/O heavy are going to suffer (hostings and databases are two common examples).
5. The patch can be disabled in Linux by passing argument to kernel during boot; however it is not advised for pretty much obvious reasons.
6. For gamers: this is not going to affect games (because those are not I/O heavy)
Meltdown: "Meltdown" targeted on desktop chips can read kernel memory from L1D cache, Intel is only affected with this variant. Works on only Intel.
Spectre: Spectre is a hardware vulnerability with implementations of branch prediction that affects modern microprocessors with speculative execution, by allowing malicious processes access to the contents of other programs mapped memory. Works on all chips including Intel/ARM/AMD.
For updates refer the kernel tree: https://git.kernel.org/…/ke…/...
For further details and more chit-chats refer: https://lwn.net/SubscriberLink/...
~Cheers~
(Originally written by Adhokshaj Mishra, edited by me. )
22 -
Anyone looking for something interesting to do???
Step 1) understand how basic circuitry works on a bread board nothing too fancy. ( Implement NAND, AND, ADDER, SUBTRACTOR)
Step 2) learn about microprocessors and how OS works
Step 3) learn assembly
Step 4)write a basic assembler and understand how loaders and linkers works !
Step 5) write a kernel with very basic features like memory management and process management and some drivers for IO
Step 5) write an emulator for some simple systems .! ex chip-8.
Step 6) read about compiler theory and automata
Step 7) write a basic Python interpreter that compiles (not interpreter) to native assembly.
Step 8) implement TCP stack .
Step 9) learn as much as u can about complexity measurement ), data structures and algorithms using C or C++ it's very important ( familiarity with pointers and thus computer memory )
Step 10) learn any high level language of choice like Python or Ruby.
Step 11) stop debating over tabs vs spaces , emacs vs vim , angular vs vue, php vs Python , OOps vs procedular vs functional ( just know about all of them and when to use but don't fucking debate over which one is superior )..
Step 12) live happily and be healthy.30 -
That feeling when you have been working on tiny microprocessors and questioned your self for every declared byte, and suddenly gets to work on the serverside of the project.
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Junior asks me to help him with his Microprocessors project. I was like cool mail it to me I'll check it out. He sends me a .s assembly file and tells me this is machine generated code, can you make it look like it's written by a human. I was like wtf dude -_-.
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I’m juggling 3 reference books for a microprocessor course this semester. Have to study 8085 and 8086 microprocessors and interfacing them. Everything seems more interesting when exams are near I swear. I find this course genuinely interesting now9
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Can anyone help me with this theory about microprocessor, cpu and computers in general?
( I used to love programming when during school days when it was just basic searching/sorting and oop. Even in college , when it advanced to language details , compilers and data structures, i was fine. But subjects like coa and microprocessors, which kind of explains the working of hardware behind the brain that is a computer is so difficult to understand for me 😭😭😭)
How a computer works? All i knew was that when a bulb gets connected to a battery via wires, some metal inside it starts glowing and we see light. No magics involved till now.
Then came the von Neumann architecture which says a computer consists of 4 things : i/o devices, system bus ,memory and cpu. I/0 and memory interact with system bus, which is controlled by cpu . Thus cpu controls everything and that's how computer works.
Wait, what?
Let's take an easy example of calc. i pressed 1+2= on keyboard, it showed me '1+2=' and then '3'. How the hell that hapenned ?
Then some video told me this : every key in your keyboard is connected to a multiplexer which gives a special "code" to the processer regarding the key press.
The "control unit" of cpu commands the ram to store every character until '=' is pressed (which is a kind of interrupt telling the cpu to start processing) . RAM is simply a bunch of storage circuits (which can store some 1s) along with another bunch of circuits which can retrieve these data.
Up till now, the control unit knows that memory has (for eg):
Value 1 stored as 0001 at some address 34A
Value + stored as 11001101 at some address 34B
Value 2 stored as 0010 at some Address 23B
On recieving code for '=' press, the "control unit" commands the "alu" unit of cpu to fectch data from memory , understand it and calculate the result(i e the "fetch, decode and execute" cycle)
Alu fetches the "codes" from the memory, which translates to ADD 34A,23B i.e add the data stored at addresses 34a , 23b. The alu retrieves values present at given addresses, passes them through its adder circuit and puts the result at some new address 21H.
The control unit then fetches this result from new address and via, system busses, sends this new value to display's memory loaded at some memory port 4044.
The display picks it up and instantly shows it.
My problems:
1. Is this all correct? Does this only happens?
2. Please expand this more.
How is this system bus, alu, cpu , working?
What are the registers, accumulators , flip flops in the memory?
What are the machine cycles?
What are instructions cycles , opcodes, instruction codes ?
Where does assembly language comes in?
How does cpu manipulates memory?
This data bus , control bus, what are they?
I have come across so many weird words i dont understand dma, interrupts , memory mapped i/o devices, etc. Somebody please explain.
Ps : am learning about the fucking 8085 microprocessor in class and i can't even relate to basic computer architecture. I had flunked the coa paper which i now realise why, coz its so confusing. :'''(14 -
Half of the courses we had in our college were about electronics. Except Microprocessors and Transistors, it's not relevant.
We even had chemistry and engineering drawing. So we essentially wasted more than half of our time.
Besides languages, weren't taught anything about real world software development.
Nothing about how to work with an existing code base, version control, design patterns, system design, creating a website, debugging, functional programming, scalability, reliability.
The industry should be involved in setting the syllabus and also contributing part time teachers.3
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