Re: Detecting illegal memory access

["linux-os \(Dick Johnson\)" <linux-os@analogic.com>]

On Tue, 11 Apr 2006, Jan Engelhardt wrote:

> Hello,
>
>
> I am looking for a way to check from userspace if a given address can be
> dereferenced. One way would be to examine /proc/self/maps if there is
> something mapped and 'r' at the address, but this seems a little time
> consuming. Is there another way? Kernelspace does have it I think, as
> access_ok().
>
>
> Jan Engelhardt
> --

A user program can trap EFAULT. However, you need to use siglongjmp()
to get back into your program and continue, plus you need to do very
careful coding to mask and unmask the appropriate signals though it
all. Since protection is on a per-page basis, one could make a program
that attempts to R/W from virtual page 0 on up, recoding success or
failure for each page.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.15.4 on an i686 machine (5589.42 BogoMips).
Warning : 98.36% of all statistics are fiction, book release in April.
_


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