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Date:   Fri, 31 Aug 2018 10:27:14 +0200
From:   Luc Van Oostenryck <>
To:     Jann Horn <>
Cc:     Thomas Gleixner <>,,
        Kees Cook <>, Borislav Petkov <>
Subject: Re: [PATCH] x86/dumpstack: fix address space casting in

On Thu, Aug 30, 2018 at 09:47:36PM +0200, Jann Horn wrote:
> I sloppily passed a kernel-typed pointer to __range_not_ok(), and sparse
> doesn't like that.
> Make `prologue` a __user pointer (to protect against accidental
> dereferences) and force-cast it to a kernel pointer when calling
> probe_kernel_read(), which will then immediately force-cast it back to a
> user pointer.

It's a bit sad to have to do this.
__range_not_ok() explicitly requires a __user pointer (I don't know
if there is a good reason for it) but  the real job is done by
__chk_range_not_ok(). Can't you use this later instead?

-- Luc Van Oostenryck

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