Re: [uml-devel] a question about sigsetjmp() in copy_from/to_user()

[Blaisorblade <bla...@ya...>]

On Tuesday 27 September 2005 19:28, Jeff Dike wrote:
> On Tue, Sep 27, 2005 at 10:06:53AM -0400, Young Koh wrote:
> > my question is, if so, shouldn't the error be caught when UML kernel
> > translates the user space address to the kernel space address? i mean,
> > UML kernel must know the valid memory regions and if the address is
> > out of the valid regions, then it knows the address is invalid before
> > UML tries to access the address. why should it use sigsetjmp() and let
> > a segfault occur?
>
> Because the address may be fine, and an access may still cause a segfault.
>
> UML memory is backed by a file on the host.  You can map anything from
> the file you want, but if you access it when the host filesystem is full
> or you've exceeded your disk quota, the access will segfault.
That wasn't the original reason - this is fine too, but as I explained in the 
other mail, cat /dev/kmem will cause a copy_to_user() with invalid kernel 
("from") address. I remember because I discussed this with you at length.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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