7 ms·
2-14% performance drop sounds high, I understand people are sceptical. Maybe the subsystems can be structured in a different way to ease the effects of ASI? Pe
by kramerger 4y ago
2-14% performance drop sounds high, I understand people are sceptical. Maybe the subsystems can be structured in a different way to ease the effects of ASI?
Personally, I would rather see a kernel side MPU in feature CPUs
- tptacek 4y agoIt's 2-14% offset potentially by whatever the cost is of the other mitigations that it replaces, for whatever that's worth.
- Filligree 4y agoI’m just going to keep turning all mitigations off, thanks.
- Veliladon 4y agoYou do you but I hope you've also turned off JavaScript in your web browser.
- netr0ute 4y agoI keep my important info on paper.
- coldpie 4y agoIs there any evidence of anyone actually attempting such an attack outside a carefully controlled research scenario? The number of stars that have to align for this theoretical attack to work in practice is so high that I don't think any normal desktop end-user has reason to worry about it. (Shared servers, co-hosted VMs, etc are a different story.)
- garaetjjte 4y agoI think there might be herd immunity effect to that: because mitigations are enabled by default, there isn't much focus for developing attacks for it.
- totony 4y agoBrowser lowered timer resolution to mitigate most speculative execution attacks. Probably why there aren't useful exploits. I remember a js payload when the first spectre appeared.
- Veliladon 4y agoTrue there isn't at the moment but do you really want to be the first to find out because you left the back door open?
- renewiltord 4y agoI am going to tell you guys something magical. There are multiple hundreds of millions of cryptocurrency running on hardware with spectre/meltdown mitigations off. Go get them.
- coldpie 4y agoI'd liken it to refusing to leave your house because you're worried a meteor may strike you down. You're giving up a lot for not much reason.
- staticassertion 4y agoNot quite. A meteor is an object with no drive or desire. Attackers are adversarial and thoughtful. You can't liken a random event to a purposeful act like this. It's more like saying "refusing to leave your house because you're worried you might get mugged", which might actually be very reasonable if you live in a bad neighborhood, you're a common target of crime, etc. It may not be reasonable for many others. But analogies are pretty rough in general.
- astrange 4y agoWhy do you want to let driver memory bugs overwrite random kernel memory?
- anvic 4y agoFor most of us driver memory bugs are extremely rare and therefore a 2-14% performance drop is bonkers.
- mrguyorama 4y agoMy AMD GPU driver bugs out pretty regularly. Hardware companies are not known for their bulletproof driver code.
- astrange 4y agoAnything you're not testing regresses, and any driver you let out of jail is going to regress too. Properly engineered security fixes don't cause performance regressions, either because you find improvements to pay for them, or you get the hardware updated to make them cheaper. (That'd be PCID in this case.)
- saagarjha 4y agoBoth of these cost money.
- hinkley 4y agoCorrect me if I’m wrong, but wouldn’t complicated page mapping affect the cost of system calls the most? Because each call causes two alterations to the MMU state. I wonder how this patch interacts with io_uring. If kernel call overhead keeps going up it will force people to find ways to avoid the overhead.
- gpderetta 4y agoIf I understand correctly the patch at the moment doesn't affect system calls at all, only entering and exiting virtual machines.
- junon 4y agoNo. This is unavoidable. Mapping physical pages into a local page table is expensive no matter how you spin it. Depending on the data structures, this means doubling the time in some cases to allocate a physical page, which is typically 4KiB. Large allocations mean multiple page allocations. It adds up.