linux-kernel - Re: [PATCH 09/20] signal/vm86_32: Replace open coded BUG_ON with an actual BUG

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Message-ID: <CAHk-=widK1vko2EN9PtV3jTo02u-expXxozui-fsK-0uKrcGHg@mail.gmail.com>
Date:   Fri, 12 Nov 2021 12:40:48 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Brian Gerst <brgerst@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        H Peter Anvin <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 09/20] signal/vm86_32: Replace open coded BUG_ON with an
 actual BUG_ON

On Fri, Nov 12, 2021 at 11:57 AM Eric W. Biederman
<ebiederm@...ssion.com> wrote:
>
> Still user space would have had to have mapped address 0 to get that
> value set in do_sys_vm86.

You have to map address 0 anyway just to get vm86 mode to work.

vm86 mode fundamentally requires the low 1MB of virtual memory to be
mapped, since there is no virtual memory offset in the vm86 model.

             Linus