linux-kernel - Re: [PATCH RFC] uaccess: user_access_begin_after_access

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Message-ID: <CAHk-=wgYu+qk15_NpUZXwbetEU5eiWppJ=Z_A6dCSCWKxCfDfw@mail.gmail.com>
Date:   Tue, 2 Jun 2020 13:43:20 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Jason Wang <jasowang@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH RFC] uaccess: user_access_begin_after_access_ok()

On Tue, Jun 2, 2020 at 1:33 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> Hmm are you sure we can drop it? access_ok is done in the context
> of the process. Access itself in the context of a kernel thread
> that borrows the same mm. IIUC if the process can be 32 bit
> while the kernel is 64 bit, access_ok in the context of the
> kernel thread will not DTRT.

You're historically expected to just "set_fs()" when you do use_mm().

Then we fixed it in commit...

Oh, when I look for it, I notice that it still hasn't gotten merged.
It's still pending, see

  https://lore.kernel.org/lkml/20200416053158.586887-4-hch@lst.de/

for the current thing.

              Linus