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

[Young Koh <young.koh@gmail.com>]

so, as my understanding, sigsetjmp() is used for returning an error
when there is a userspace and/or kernelspace address faulting in both
skas and tt modes. and i386 implementation works the same way, i
guess.

my one quick question is (it could sound stupid, but) that why there
may be a kernelspace faulting? kernel must correct and shouldn't
access bad address, i guess, and if so, shouldn't it be a kernel
panic?

> In fact, what you see doesn't catch user space wrong addresses.
>
> It catches kernelspace faulting addresses - which is legal to happen, because
> i386 implementation catches any fault, and doesn't make a distinction, and
> which happens, when you try to do things like "cat /dev/kmem" - you're trying
> to do copy_to_user(to, offset /* which is 0 */, size).
>
> In fact, that sigsegjmp() was added back in 2.4.24-?um (IIRC) and then around
> ~2.6.7-um after I and Jeff analyzed this.

i'm using 2.4.26 and 2.6.12 and i think both versions include sigsetjmp().

Thank you,

-Young


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