1 stable 2 super stable

[dandy72]

trønderen wrote:

The OS may trust itself.

That's a mistake if that's the case. I thought Windows these days only established trust by signing *every* file in the Windows folder (where practical).

[trønderen]

"Trust" in the sense "May allow its own components write access to data structures that noone else trusted to modify". If it didn't trust itself to set up segment/paging tables, interrupt handlers etc., nothing could ever work. Signing is a different sort of trust.

[Calin Negru]

> super duper stable I don’t think that is out yet. Who knows, maybe Windows 12 will fit the requirements. Although some might say there’s not much space for improvement left.

[trønderen]

The hardware offering certainly is there. A specific OS is not obliged to make use of it. The 386 segment system looks like it was hand crafted to Windows of the day. But MS made attempts to make Window the universal OS for all sorts of processors (such as MIPS, Alpha, PowerPC, Itanium, ...). Since they do not all provide the same hardware support, MS chose to limit themselves to the bare minimum available on all processors and do their own software simulation, identical for all of it. The same goes for the protection system: They ignored all advanced mechanisms. All users shall have the same offering; we cannot give x86/x64 users a protection mechanism unavailable to users on other platforms. Of course they could have designed a hardware abstraction layer that modelled both segment and ring mechanisms that could very easily be mapped to Intel hardware, but required far more software emulation on other processors (giving them a competitive disadvantage). Maybe they would have done that, if they had known at that time how other processors would dwindle away anyway. They didn't. A major factor may be that they picked up OS experts from other architectures that didn't provide such things, major design architects simply unfamiliar with how such mechanisms are used, so they ignored them. I am quite sure that at least you were right, that Windows ignored the intermediate privilege levels (along with the segment mechanisms). I thought that in order to make a more robust kernel, they started pushing external drivers down to ring 1 a while ago. I may very well be wrong. Maybe what I have read is unfounded speculations, and I found it such a natural thing to do that I took for granted that the change was carried through. If the OS code is structured like a crow's nest it might be very difficult to realize, though. I have strong suspicions that the current state of the Windows implementation is not quite what you would use as a model system if you were teaching a university level course in well-designed OS implementation.

[Matt Bond]

"Intend your puns, weaklings" - Old Fire Emblem game.

Bond Keep all things as simple as possible, but no simpler. -said someone, somewhere

[dandy72]

trønderen wrote:

Signing is a different sort of trust.

Fair enough.

[dandy72]

trønderen wrote:

I thought that in order to make a more robust kernel, they started pushing external drivers down to ring 1 a while ago.

That could very well be the case, my knowledge on this topic is years old. And Microsoft has since been spending resources on trying to re-architect at least some parts of Windows in the name of security (to what degree of success, is a matter for another discussion) :-)

trønderen wrote:

I have strong suspicions that the current state of the Windows implementation is not quite what you would use as a model system if you were teaching a university level course in well-designed OS implementation.

How very true. Software that old, with so many layers that have been added over the years decades, cannot be optimally clean.

[sasadler]

It's not frequent but I've had my Win 10 system crash. No BSOD, just acts like I'd pushed the reset button. I'm pretty sure it's only been when I was gaming (which I do frequently now that I'm retired!). I do use the latest and greatest drivers for my GPU so possibly a driver issue.

[jschell]

Calin Negru wrote:

and did not dispose things properly (leaving a mess behind in your app on exit) the OS would have been unforgiving

I don't remember anything like that. For example pipes did not exist. So certainly no way to leave one of those around. Files were closed when the app exited. Memory was returned when the app exited. Pretty sure sockets were closed when the app exited. Not sure about UI 'handles' but I think they were returned too, probably because they were actually virtual and handled in memory (see above.) Now all of that is true. Except it is possible to leave a named pipe hanging around but that is pretty much exactly the point (the programmer, not the OS, is responsible for the lifetime.) Keep in mind of course that right now, because of the way sockets are defined, when the app exits the sockets are not immediately closed. The protocol must be respected. But now and then if you have an open client socket and either unplug (hardware) from the network, crash the computer or power off the computer then the socket is, by definition, still open.

Calin Negru wrote:

On Windows 10 if you leave a mess on exit the OS won’t say a thing no dialog boxes or messages telling you about corrupted memory, or that the app has exited with errors.

As stated that is not possible. Regardless of how the application exits the memory is returned to the OS. Even if you overwrite the application stack and/or code space the memory will still be returned. With older OSes it was easier to write into spaces where one shouldn't. Which is not the same as saying it was easy. Nor is one absolutely precluded from doing it now.

[jochance]

It's the goal that is basically unreachable for Windows as well and I think Linux has to necessarily be limited in how much better it can be in that regard. At some point you're talking hardware and any OS is going to have the same problems/limitations. I probably read about it from an article on here, but pretty much every modern Intel processor will give you whatever memory you want, maybe even let you write it (I can't remember), and they say you can patch this... I've no idea how you possibly patch this. Apparently, applying the patch can reduce performance by 50%. IMO, some of these expectations of user vs kernel memory space are simply out of whack with the realities. The whole TPM windows 11 debacle is kind of a highlighter pen at the heart of why expectations in this regard are misaligned with reality. The hardly-oversimplification is that something, somewhere has to be the authority of what's right/ok. That authority essentially builds the walls to delineate user vs kernel memory. Right now, this is pretty much software with not so much hardware involvement aside from some limited specific things/use cases. Maybe over the next decade we'll actually see things built at the hardware level that enable this to happen instead of just basically faking it at the software level. I think this will require something like FPGAs being able to dynamically build the interfaces between CPU and RAM for the application/software on demand (while also verifying against security permissions whether the structure should be allowed).