In message <[EMAIL PROTECTED]>, Bernd Walter writes:
>On Tue, Sep 25, 2001 at 10:01:03AM +0200, Peter Wullinger wrote:
>> On Tue, Sep 25, 2001 at 09:56:07AM +0200, Bernd Walter wrote:
>> > On Mon, Sep 24, 2001 at 06:14:34PM -0700, Bakul Shah wrote:
>> > > FWIW, in a Unix port we did I remember putting the user
>> > > struct *above* the kernel stack. The stack grew down so you
>> > > hit the red zone (the guard pages) without clobbering the
>> > > user struct. Since struct user _ended_ on a page boundary,
>> > > its size was needed at locore.s assembly time but that was a
>> > > small price to pay for the added safety.
>> >
>> > I don't think a guard page can help here, because the page fault
>> > handler needs a working stack.
>> >
>> Depends on what is does ... if it just panics and syncs and does
>> not care overwriting the user struct of the current process (which
>> is lost anyway), is this much of a problem?
>
>Please correct me if I'm missing something.
>If it is overwriting there is no page fault thus no guard page and
>no panic.
>If you would have a page fault there is no space where the CPU can
>write the state information to for entering the handler.
And it would take a double-fault for which we have a handler with
it's own stack.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
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FreeBSD committer | BSD since 4.3-tahoe
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