linux-kernel - Re: [PATCH 37/50] x86/boot/e820: Use 'enum e820_type' in 'struct e820

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CA+55aFxSgQZVmefbzWgNa6Af3+HDN=zZQnV_OactcJRD1YMHKA@mail.gmail.com>
Date:   Sat, 28 Jan 2017 15:07:03 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH 37/50] x86/boot/e820: Use 'enum e820_type' in 'struct e820_entry'

On Sat, Jan 28, 2017 at 2:11 PM, Ingo Molnar <mingo@...nel.org> wrote:
> Use a stricter type for struct e820_entry. Add a build-time check to make
> sure the compiler won't ever pack the enum into a field smaller than
> 'int'.

I'm not sure this is a good idea. In fact, I'm pretty sure it's a horrible idea.

The compiler that *users* use might decide that the "enum" fits in a
8-bit unsigned char, and decide to use that. The kernel build won't
notice and the BUG_ON() won't help, because we use a different
compiler.

(Or even if it's the same compiler you can have build flags - the size
of an enum very much depends on various compiler options, particularly
"--short-enums" for gcc).

Basically, we should not use "enum"s in types exported to user space.
The size just isn't sufficiently well defined, and it's a maintenance
nightmare.

Use explicitly sized members only, please. No "enum".

            Linus