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-=whf-nR4xDSEDtXeowFn4QQKY3s_MXoM8Ha-dPiOzFzUxQ@mail.gmail.com>
Date:   Fri, 12 Nov 2021 13:23:16 -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 1:04 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> Still if we are going to check for userspace being silly that it should
> be in do_sys_vm86.

Sore, something like

        if (!user_vm86)
                return -EINVAL;

in do_sys_vm86() sounds fine to me.

It could in theory break some odd test-case, but I can't see anybody
putting the vm86 save area at 0 in a real situation.

But I could see some quick test hack doing it - the IVT at boot is
actually not at zero, but at fffxxxxx. 8086 is magic.

              Linus