linux-kernel - Re: [PATCH v2 14/18] lib/test_lockup: fix kernel pointer check for separate address spaces

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Message-ID: <20220218063549.GJ22576@lst.de>
Date:   Fri, 18 Feb 2022 07:35:49 +0100
From:   Christoph Hellwig <hch@....de>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>, linux-arch@...r.kernel.org,
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Subject: Re: [PATCH v2 14/18] lib/test_lockup: fix kernel pointer check for
 separate address spaces

On Wed, Feb 16, 2022 at 02:13:28PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> test_kernel_ptr() uses access_ok() to figure out if a given address
> points to user space instead of kernel space. However on architectures
> that set CONFIG_ALTERNATE_USER_ADDRESS_SPACE, a pointer can be valid
> for both, and the check always fails because access_ok() returns true.
> 
> Make the check for user space pointers conditional on the type of
> address space layout.

What is this code even trying to do?  It looks extremly broken.