Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 12 Dec 2017 10:03:19 -0800 | Subject | Re: [patch 00/16] x86/ldt: Use a VMA based read only mapping |
| |
On Tue, Dec 12, 2017 at 9:32 AM, Thomas Gleixner <tglx@linutronix.de> wrote: > Peter and myself spent quite some time to figure out how to make CPUs cope > with a RO mapped LDT. > > While the initial trick of writing the ACCESS bit in a special fault > handler covers most cases, the tricky problem of CS/SS in return to user > space (IRET ...) was giving us quite some headache. > > Peter finally found a way to do so. Touching the CS/SS selectors with LAR > on the way out to user space makes it work w/o trouble. > > Contrary to the approach Andy was taking with storing the LDT in a special > map area, the following series uses a special mapping which is mapped > without the user bit and read only. This just ties the LDT to the process > which is the most natural way to do it, removes the requirement for special > pagetable code and works independent of pagetable isolation. > > This was tested on quite a range of Intel and AMD machines, but the test > coverage on 32bit is quite meager. I'll resurrect a few dust bricks > tomorrow.
I think it's neat that you got this working. But it's like three times the size of my patch, is *way* more intrusive, and isn't obviously correct WRT IRET and load_gs_index(). So... how is it better than my patch?
| |