user malloc from kernel

Peter Pentchev roam at ringlet.net
Mon Sep 29 08:56:20 PDT 2003


On Mon, Sep 29, 2003 at 05:47:41PM +0200, Pawel Jakub Dawidek wrote:
> On Mon, Sep 29, 2003 at 05:22:47PM +0300, earthman wrote:
> +> how to allocate some memory chunk
> +> in user space memory from kernel code?
> +> how to do it correctly?
> 
> Here you got sample kernel module which do this:
> 
> 	http://garage.freebsd.pl/usmalloc.tgz
> 	http://garage.freebsd.pl/usmalloc.README

Errrr... but won't this interfere *badly* with userland programs
which attempt to allocate memory after making the syscall in question?
I mean, won't the application's memory manager attempt to allocate the
next chunk of memory right over the region that you have stolen with
this brk(2) invocation?  Thus, when the application tries to write into
its newly-allocated memory, it will overwrite the data that the kernel
has placed there, and any attempt to access the kernel's data later will
fail in wonderfully unpredictable ways :)

G'luck,
Peter

-- 
Peter Pentchev	roam at ringlet.net    roam at sbnd.net    roam at FreeBSD.org
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