Messages in this thread | | | Date | Tue, 26 Jul 2011 08:18:27 +0100 | From | "Jan Beulich" <> | Subject | Re: git commit 9fd67b4ed0714ab718f1f9bd14c344af336a6df7 (x86-64: Give vvars their own page) breaks Xen PV guests (64-bit). |
| |
>>> On 25.07.11 at 20:10, Andrew Lutomirski <luto@mit.edu> wrote: > On Mon, Jul 25, 2011 at 12:10 PM, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote: >> However, this is what I get later on, any ideas? > >> [ 0.585880] init[1] illegal int 0xcc from 32-bit mode ip:ffffffffff600400 > cs:e033 sp:7fff230ca088 ax:ffffffffff600400 si:7faee3e822bf di:7fff230ca158 > > That will, indeed, crash your system. > > 0xe033 is FLAT_RING3_CS64 > > Jeremy / other Xen people: I'm trying to implement a lightweight > check to distinguish a trap from a sane (i.e. allowable for syscalls) > 64-bit user context from anything else. There seems to be precedent > for using ->cs == __USER_CS to detect 64-bitness; for example, step.c > contains: > > #ifdef CONFIG_X86_64 > case 0x40 ... 0x4f: > if (regs->cs != __USER_CS) > /* 32-bit mode: register increment */ > return 0; > /* 64-bit mode: REX prefix */ > continue; > #endif > > The prefetch opcode checker in mm/fault.c does something similar.
That (namely the latter) has been in place basically forever (also in the original http://xenbits.xen.org/hg/linux-2.6.18-xen.hg/ tree), but indeed would seem to need addition of a check against Xen's ring-3 64-bit CS. It's just that in the pre-existing cases the consequences are at worst moderate...
Jan
| |