On Mon, Jan 31, 2005 at 01:58:31 +0000, Jon Masters wrote: > On Fri, 21 Jan 2005 12:59:59 +0100, Arjan van de Ven > <arjan@xxxxxxxxxxxxx> wrote: > > On Thu, 2005-01-20 at 12:54 -0600, Timur Tabi wrote: > > > I recently discovered in a driver I'm working on that there are several > > > places where a user-space virtual address is being dereferenced > > > successfully. I was under the impression that that should not work - > > > user pointers should not be usuable in kernel space. > > > > it may work. you may be lucky. The page also may be swapped out and you > > crash and burn > > > as for fc2/3; those kernels have a separate address space for user and > > kernel, and as a result such rogue accesses will almost always crash, > > not just sometimes. > > You know, I had wondered what use this patchset had other than for > folks with 32bit systems straining under userspace limits - this is > actually a pretty cool driver diagnostic tool in and of itself :-) Wait a second... Separate address spaces for user and kerenl space? That means switching page tables on each kernel entry/exit. That means tlb flush on each interrupt. That would mean quite a slowdown. ------------------------------------------------------------------------------- Jan 'Bulb' Hudec <bulb@xxxxxx>
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