Talk:1938: Meltdown and Spectre

Explain xkcd: It's 'cause you're dumb.
Revision as of 20:19, 5 January 2018 by DPS2004 (talk | contribs)
Jump to: navigation, search


The "trolley problem" is the ethical dilemma thought experiment where an out-of-control trolley is heading to a junction (which you have control over) - to one side it'll kill one group of people - to the other, some others. Your moral dilemma is deciding which is the "best" outcome (eg, hitting a dozen five year old children or three Nobel laureats). This is like a software "if" statement. Speculative execution in most CPU chips is where the computer always takes both sides of a decision like this - explores what will happen down each path - and only causes the effects of the decision to happen when the decision as to which way to proceed is decided. This allows it to keep on doing useful work while some slower decision is made. The "quantum" aspect of this is that in some versions of quantum theory, quantum-level particles take every possible path at once and the result is the sum of all of them.

In a sense, the computer is exploring the consequences of the trolley problem in a quantum-like manner.

This would all be OK if it were not for the fact that devious black-hat hackers can come up with devious ways to see the information that should have been discarded in the "path-not-taken". So even though the computer will eventually decide that some piece of information should not be accessible - you can find out the value it would hypothetically read - even though it will soon decide that it should not access the information.

The "rowhammer" problem is something entirely different. Computer memories are organized as a two-dimensional grid of rows and columns - and are physically constructed from tiny capacitors. If you apply just the RIGHT pattern of rapid changes to one row of the grid, you can cause one of the capacitors on the next row to incorrectly change state. This is a design flaw in the memory chip - and it allows (in some circumstances) programs to change data in memory locations that they have no right to change.

SteveBaker (talk) 19:33, 5 January 2018 (UTC)

uhhh did you just copy and paste your entire edit into talk? DPS2004'); DROP TABLE users;-- (talk) 20:19, 5 January 2018 (UTC)