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    SubjectRe: copy_from_user/copy_to_user question
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    On Sat, 2005-12-03 at 01:38 +0000, Al Viro wrote:
    > On Fri, Dec 02, 2005 at 08:09:59PM -0500, Steven Rostedt wrote:
    > > > Secondly, they seem to use memcpy as opposed to using
    > > > copy_to_user/copy_from_user which is also very
    > > > dangerous.
    > >
    > > If they are grabbing data from user context into kernel (or vise versa)
    > > that could easily cause an oops. Not to mention it is a security risk.
    >
    > Not to mention it simply won't work on a many platforms, no matter what...

    Hmm, I've only worked with a few platforms (i386, x86_64, ppc, mips, and
    a little arm but I don't remember that much). I believe that a memcpy
    could work on all these platforms (error prone of course, but if the
    memory is mapped its OK). When entering a system call, the kernel still
    has access to the memory locations assigned to the user.

    It's been a while since I had to deal with the semantics of
    copy_to/from_user. So what platforms can not access a user space area
    directly. Is there a special assembly command to use to copy from user?

    I haven't dealt (yet) with the copy_user of x86_64. Is there a problem
    when one tries to copy to/from a 32 bit address while in a 64 bit
    address space?

    Just curious, sorry for my ignorance here.

    -- Steve


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