Linux Will End Up Disabling x86 PTI For AMD Processors - Update: Now Disabled
Update: Linus Torvalds has now ended up pulling the latest PTI fixes that also include the change to disable page table isolation for now on all AMD CPUs. The commit is in mainline for Linux 4.15 along with a few basic fixes and ensuring PAGE_TABLE_ISOLATION is enabled by default.
Kernel developer Thomas Gleixner wrote in the pull request of disabling KPTI on AMD hardware, "Not necessarily a fix, but if AMD is so confident that they are not affected, then we should not burden users with the overhead."
phoronix.com
So, to recap: There are two exploits uncovered related to speculative execution on modern processors, and these are known as Meltdown and Spectre.
With regard to the Meltdown exploit (gaining access to kernel memory), the performance-reducing patch will not be enforced on Linux systems running on AMD processors, as this issue does not affect AMD processors, due to architecture differences. Hopefully, Windows will apply the patch selectively as well.
While all modern out-of-order processors are, in theory, susceptible to the Spectre exploit (gaining access to another process' memory), this can be mitigated in software with negligible performance impact, and/or the known/demonstrated attacks have not been shown to work on AMD processors, as I understand it. Hence, AMD states "near zero risk". |
