Protecting against kernel NULL-pointer derefs

[Garance A Drosihn]

At 12:13 AM +0900 9/19/09, Hideki EIRAKU wrote:
>From: Pieter de Boer <pieter at thedarkside.nl>
>Subject: Protecting against kernel NULL-pointer derefs
>Date: Tue, 15 Sep 2009 10:03:48 +0200
>
>>  - Are there unwanted side-effects of raising VM_MIN_ADDRESS?
>
>Mapping at address 0x0 is needed by some softwares using vm86 mode.
>For example, emulators/doscmd uses vm86 mode to emulate an old DOS
>environment. In this case, the address 0x0 - 0x3ff is used for an
>interrupt vector of emulated DOS world. If VM_MIN_ADDRESS is not
>zero, doscmd doesn't work. vm86 mode is in 32bit i386 architecture
>only, not in amd64 or other architectures.

Could we:

a) alter those programs so they didn't need that vector in page 0?

or

b) provide some system call or other facility which would allow
    *that* process to use page 0?

-- 
Garance Alistair Drosehn            =   gad at gilead.netel.rpi.edu
Senior Systems Programmer           or  gad at freebsd.org
Rensselaer Polytechnic Institute    or  drosih at rpi.edu