Re: [PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem)

From: Dave Jones (davej_at_redhat.com)
Date: 08/12/05

  • Next message: Steven Rostedt: "Re: [PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem)" 
    Date:	Fri, 12 Aug 2005 12:56:57 -0400
To: Linus Torvalds <torvalds@osdl.org>

    On Fri, Aug 12, 2005 at 09:35:03AM -0700, Linus Torvalds wrote:

    > On Thu, 11 Aug 2005, Steven Rostedt wrote:
    > >
    > > Found the problem. It is a bug with mmap_kmem. The order of checks is
    > > wrong, so here's the patch. Attached is a little program that reads the
    > > System map looking for the variable modprobe_path. If it finds it, then
    > > it opens /dev/kmem for read only and mmaping it to read the contents of
    > > modprobe_path.
    >
    > I'm actually more inclined to try to deprecate /dev/kmem.. I don't think
    > anybody has ever really used it except for some rootkits. It only exists
    > in the first place because it's historical.

    We've had it disabled in Fedora for a long time, maybe as far
    back as FC2, for exactly this reason. The only things that broke,
    were things that needed fixing anyway. (Something like gdm was
    reading /dev/mem to get a source of random numbers of all things).

    > We do need to support /dev/mem for X, but even that might go away some
    > day.

    We also restrict /dev/mem to be a 'need to know' basis. Trying
    to read from certain regions of memory will fail.
    Again, nothing that wasn't already broken broke with this change.

    > So I'd be perfectly happy to fix this, but I'd be even happier if we made
    > the whole kmem thing a config variable (maybe even default it to "off").

    The above patches were in -mm for a while, though they didn't
    have a config option, they just 'did it', and some of the
    changes were a bit unclean, but I can polish that up if you're
    interested.

                    Dave

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  • Next message: Steven Rostedt: "Re: [PATCH] Fix mmap_kmem (was: [question] What's the difference between /dev/kmem and /dev/mem)"

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