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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun, 6 Oct 2019 20:12:33 -0700
Message-ID: <CAHk-=whKUHYSj2iZTaVKHuRve-=V6GJem78Uh6FkGb4pwYZd3Q@mail.gmail.com>
Subject: Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user()
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
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On Sun, Oct 6, 2019 at 7:30 PM Guenter Roeck <linux@roeck-us.net> wrote:
>
> > Mind humoring me and trying that on your alpha machine (or emulator,
> > or whatever)?
>
> Here you are. This is with v5.4-rc2 and your previous patch applied
> on top.
>
> / # ./mmtest
> Unable to handle kernel paging request at virtual address 0000000000000004

Oookay.

Well, that's what I expected, but it's good to just have it confirmed.

Well, not "good" in this case. Bad bad bad.

The fs/readdir.c changes clearly exposed a pre-existing bug on alpha.
Not making excuses for it, but at least it explains why code that
_looks_ correct ends up causing that kind of issue.

I guess the other 'strict alignment' architectures should be checking
that test program too. I'll post my test program to the arch
maintainers list.

             Linus