lkml.org 
[lkml]   [2015]   [Sep]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: stop breaking dosemu (Re: x86/kconfig/32: Rename CONFIG_VM86 and default it to 'n')
    From
    Date
    On 2015-09-04 06:46, Stas Sergeev wrote:
    > 04.09.2015 13:09, Chuck Ebbert пишет:
    >> On Fri, 4 Sep 2015 00:28:04 +0300
    >> Stas Sergeev <stsp@list.ru> wrote:
    >>
    >>> 03.09.2015 21:51, Austin S Hemmelgarn пишет:
    >>>> There are servers out there that have this enabled and _never_ use it
    >>>> at all,
    >>> Unless I am mistaken, servers usually use special flavour of the
    >>> distro (different from desktop install), where of course this will
    >>> be disabled _compile time_.
    >> Many (most?) distros use just one kernel for everything, because it's
    >> just too much work to have a separate flavor for servers.
    > But for example menuconfig promotes CONFIG_PREEMPT_NONE for server
    > and CONFIG_PREEMPT for desktop. Also perhaps server would need an
    > lts version rather than latest.
    > I wonder if RHEL Server offers the generic desktop-suited kernel
    > with vm86() enabled?
    >
    > In any case, if there is some generic mechanism to selectively
    > disable syscalls at run-time for server, then vm86() is of course
    > a good candidate. I wonder how many other syscalls are currently
    > run-time controlled? (those that are not marked as an "attack surface"
    > and defaulted to Y; I suppose the "attack surface" is currently only vm86())
    >
    OK, I think I need to clarify something here.

    The attack surface of a given system refers to the number of different
    ways that someone could potentially attack that system. An individual
    syscall is not in itself an attack surface, but is part of the attack
    surface for the whole system. One of the core concepts of proactive
    security is to minimize the attack surface, because the fewer ways
    someone could possibly attack you, the less likely it is that they will
    succeed.

    I however, referred to vm86 as a potential attack vector, which refers
    one way in which someone could attempt to attack the system (be it
    through arbitrary code execution , privilege escalation, or some other
    type of exploit), note that something does not need to have a known
    exploit to be classified as a potential attack vector (most black hat's
    out there will keep quiet about discovered exploits until they can
    actually make use of them themselves). By their very definition, every
    single site that userspace can call into the kernel is a _potential_
    attack vector, including vm86(). vm86() is one of the more attractive
    syscalls to attempt to use as an attack vector on 32-bit x86 systems
    because it's relatively unaudited, significantly modifies the execution
    state of the processor, and is available on a majority of 32-bit x85
    systems in the wild. This does not mean that it is exploitable
    directly, just that it's a possible target for an exploit.

    [unhandled content-type:application/pkcs7-signature]
    \
     
     \ /
      Last update: 2015-09-04 15:01    [W:4.096 / U:0.200 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site