linux-kernel - Re: [PATCH v2 05/17] x86/ldt: Prevent ldt inheritance on exec

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Message-ID: <CALCETrV2WOYxXFFwDGJjtuZwBUpUyWhrr-Q1Q-CvYhVCycrtww@mail.gmail.com>
Date:   Thu, 14 Dec 2017 08:32:57 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirsky <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Will Deacon <will.deacon@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 05/17] x86/ldt: Prevent ldt inheritance on exec

On Thu, Dec 14, 2017 at 3:27 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
>
> The LDT is inheritet independent of fork or exec, but that makes no sense
> at all because exec is supposed to start the process clean.
>
> The reason why this happens is that init_new_context_ldt() is called from
> init_new_context() which obviously needs to be called for both fork() and
> exec().
>
> It would be surprising if anything relies on that behaviour, so it seems to
> be safe to remove that misfeature.
>
> Split the context initialization into two parts. Clear the ldt pointer and
> initialize the mutex from the general context init and move the LDT
> duplication to arch_dup_mmap() which is only called on fork().

I like this one.