Re: user malloc from kernel

From: Peter Pentchev (roam_at_ringlet.net)
Date: 09/29/03

  • Next message: Pawel Jakub Dawidek: "Re: user malloc from kernel" 
    Date: Mon, 29 Sep 2003 18:56:13 +0300
To: Pawel Jakub Dawidek <nick@garage.freebsd.pl>

    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@ringlet.net    roam@sbnd.net    roam@FreeBSD.org
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