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Date:   Tue, 21 Jul 2020 07:35:42 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     Christoph Hellwig <hch@lst.de>, Nick Hu <nickhu@andestech.com>,
        Greentime Hu <green.hu@gmail.com>,
        Vincent Chen <deanbo422@gmail.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/6] syscalls: use uaccess_kernel in
 addr_limit_user_check
Message-ID: <20200721053542.GA10301@lst.de>
References: <20200714105505.935079-1-hch@lst.de> <20200714105505.935079-2-hch@lst.de> <20200718013849.GA157764@roeck-us.net> <20200718094846.GA8593@lst.de> <20200720221046.GA86726@roeck-us.net> <20200721045834.GA9613@lst.de> <eb470677-b569-a6f0-e63b-60149b54863a@roeck-us.net> <20200721052022.GA10011@lst.de> <7fc565fe-411e-6a0b-8aaf-0bf808f0d6a9@roeck-us.net>
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On Mon, Jul 20, 2020 at 10:30:30PM -0700, Guenter Roeck wrote:
> Guess I lost it somewhere. Are you saying the check was wrong all along
> and your patch fixed it ?

Oh, it is a little complicated.

Normally we have two address space limits, KERNEL_DS and USER_DS,
and they are supposed to be different.  armnommu and m68k define them
to the same value for no good reason.  That leads to:

uaccess_kernel always returning true as it does a positive check
agains KERNEL_DS, which disables a bunch of drivers like sg and
rdma, and could also lead to really strange and probably broken
results in a few places.

It also leads to the SIGKILL in addr_limit_user_check never
triggering due to the negatіve check, which is ok as the limits
never are different.