Messages in this thread | | | Date | Tue, 22 Apr 2014 19:26:30 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE* |
| |
On Tue, Apr 22, 2014 at 10:11:27AM -0700, H. Peter Anvin wrote: > The fastpath interference is: > > 1. Testing for an LDT SS selector before IRET. This is actually easier > than on 32 bits, because on 64 bits the SS:RSP on the stack is always valid. > > 2. Testing for an RSP inside the espfix region on exception entry, so we > can switch back the stack. This has to be done very early in the > exception entry since the espfix stack is so small. If NMI and #MC > didn't use IST it wouldn't work at all (but neither would SYSCALL). > > #2 currently saves/restores %rdi, which is also saved further down. > This is obviously wasteful.
Btw, can we runtime-patch the fastpath interference chunk the moment we see a 16-bit segment? I.e., connect it to the write_idt() path, i.e. in the hunk you've removed in there and enable the espfix checks there the moment we load a 16-bit segment.
I know, I know, this is not so important right now but let me put it out there just the same.
-- Regards/Gruss, Boris.
Sent from a fat crate under my desk. Formatting is fine. --
| |