LOWRAM mmap: Invalid argument

LOWRAM mmap: Invalid argument

[ivan]

Hello,

Dosemu doesn't run any more. I use latest ubuntu hardy (frequently updated) on 3
different machines (both ia32 and amd64) and the last time I remember dosemu
working was about 2 weeks ago. Today, all I got was the following error message:

$ dosemu
LOWRAM mmap: Invalid argument
Segmentation fault (core dumped)

I tried from X and from the console, all 3 computers, result the same. Some
dependency had to break dosemu. Google doesn't give any hints about LOWRAM mmap.
So, anyone has an idea?

Thanks a lot
Ivan

Re: LOWRAM mmap: Invalid argument

[Bart Oldeman]

Hi,

you can check the value of
/proc/sys/vm/mmap_min_addr
and if it is non-zero, use
echo 0 > /proc/sys/vm/mmap_min_addr

I am not sure what Ubuntu has been up to exactly: this is something
that only works with SELinux enabled in enforcing mode.

This is the help:
+config SECURITY_DEFAULT_MMAP_MIN_ADDR
+        int "Low address space to protect from user allocation"
+        depends on SECURITY
+        default 0
+        help
+         This is the portion of low virtual memory which should be protected
+         from userspace allocation.  Keeping a user from writing to low pages
+         can help reduce the impact of kernel NULL pointer bugs.
+
+         For most users with lots of address space a value of 65536 is
+         reasonable and should cause no problems.  Programs which use vm86
+         functionality would either need additional permissions from either
+         the LSM or the capabilities module or have this protection disabled.
+
+         This value can be changed after boot using the
+         /proc/sys/vm/mmap_min_addr tunable.
+
+

I am not sure how to give DOSEMU special permission -- maybe you could
ask Ubuntu kernel maintainers about why they changed mmap_min_addr?

(o and this is speculation on my part, perhaps there is a different
problem in which case I don't know).

Bart

Re: LOWRAM mmap: Invalid argument

[ivan]

On Sat, Apr 12, 2008 at 01:51:54PM -0400, Bart Oldeman wrote:
> Hi,
> 
> you can check the value of
> /proc/sys/vm/mmap_min_addr
> and if it is non-zero, use
> echo 0 > /proc/sys/vm/mmap_min_addr

That's exactly it. Big thanks.

Ivan

> I am not sure what Ubuntu has been up to exactly: this is something
> that only works with SELinux enabled in enforcing mode.
> 
> This is the help:
> +config SECURITY_DEFAULT_MMAP_MIN_ADDR
> +        int "Low address space to protect from user allocation"
> +        depends on SECURITY
> +        default 0
> +        help
> +         This is the portion of low virtual memory which should be protected
> +         from userspace allocation.  Keeping a user from writing to low pages
> +         can help reduce the impact of kernel NULL pointer bugs.
> +
> +         For most users with lots of address space a value of 65536 is
> +         reasonable and should cause no problems.  Programs which use vm86
> +         functionality would either need additional permissions from either
> +         the LSM or the capabilities module or have this protection disabled.
> +
> +         This value can be changed after boot using the
> +         /proc/sys/vm/mmap_min_addr tunable.
> +
> +
> 
> I am not sure how to give DOSEMU special permission -- maybe you could
> ask Ubuntu kernel maintainers about why they changed mmap_min_addr?
> 
> (o and this is speculation on my part, perhaps there is a different
> problem in which case I don't know).
> 
> Bart

Re: LOWRAM mmap: Invalid argument

[marc.cunning]

Hello,
This is because the newest kernels distributions after 2.6.28.7,
defaults to: "DEFAULT_MMAP_MIN_ADDR [=4096]"
in configure defaults.

Marc

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