lkml.org 
[lkml]   [2012]   [Jan]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: Compat 32-bit syscall entry from 64-bit task!? [was: Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]
From
On Thu, January 19, 2012 02:19, Andrew Lutomirski wrote:
> On Wed, Jan 18, 2012 at 5:06 PM, Indan Zupancic <indan@nul.nu> wrote:
>> On Wed, January 18, 2012 02:01, Andrew Lutomirski wrote:
>>> On Tue, Jan 17, 2012 at 4:56 PM, Indan Zupancic <indan@nul.nu> wrote:
>>> I don't know what your ptrace jailer does. But a task can switch
>>> itself between 32-bit and 64-bit execution at will, and there's
>>> nothing the kernel can do about it. (That isn't quite true -- in
>>> theory the kernel could fiddle with the GDT, but that would be
>>> expensive and wouldn't work on Xen.)
>>
>> That's why we don't cache the CS value but check it for every system call.
>> But you said elsewhere that checking CS isn't always correct either.
>> I grepped arch/x86 for "user_64bit_mode", but couldn't find anything,
>> but maybe my kernel sources are too old, I haven't updated this system
>> for almost a year. The current code only handles 0x23 and 0x33 and kills
>> the jail if it encounters anything else.
>
> I think you're hosed on Xen, then. Xen regularly runs with a
> different Xen-specific cs value.

That's fine as long as a cs value of 0x23 or 0x33 gives reliable information.
Not running is highly prefered above running insecurely. Security first,
functionality second.

Greetings,

Indan




\
 
 \ /
  Last update: 2012-01-19 02:49    [W:0.204 / U:0.100 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site