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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 27 Oct 2020 10:00:03 -0700
Message-ID: <CAHk-=wjKhAhOF6Q5JX6a3gdcmZjFFYcBJ-JJ6wybSMHdn2M_Xg@mail.gmail.com>
Subject: Re: [PATCH] Fix compat regression in process_vm_rw()
To:     Christoph Hellwig <hch@lst.de>
Cc:     Al Viro <viro@zeniv.linux.org.uk>, Jens Axboe <axboe@kernel.dk>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Kyle Huey <me@kylehuey.com>
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On Tue, Oct 27, 2020 at 1:01 AM Christoph Hellwig <hch@lst.de> wrote:
>
> Independent of this fix I think we just need to explicitly prohibit
> cross-access.

Well, prohibiting a 32-bit process from accessing a 64-bit one might
make sense, since it fundamentally cannot work, and returning an
explicit error early might help avoid confusion.

But a 64-bit one can certainly validly look at a 32-bit one (ie
debugging a compat process from a 64-bit gdb or similar is not
unreasonable).

That said, I wonder how muich of a problem that can be, so it may be
sufficient to just fix this compat case up and leave it alone.

So applied,

            Linus