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References: <20171214112726.742649793@infradead.org> <20171214113851.348915849@infradead.org>
From: Andy Lutomirski <luto@kernel.org>
Date: Thu, 14 Dec 2017 08:32:57 -0800
Message-ID: <CALCETrV2WOYxXFFwDGJjtuZwBUpUyWhrr-Q1Q-CvYhVCycrtww@mail.gmail.com>
Subject: Re: [PATCH v2 05/17] x86/ldt: Prevent ldt inheritance on exec
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To: Peter Zijlstra <peterz@infradead.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>, X86 ML <x86@kernel.org>, Linus Torvalds <torvalds@linux-foundation.org>, Andy Lutomirsky <luto@kernel.org>, Dave Hansen <dave.hansen@intel.com>, Borislav Petkov <bpetkov@suse.de>, Greg KH <gregkh@linuxfoundation.org>, Kees Cook <keescook@google.com>, Hugh Dickins <hughd@google.com>, Brian Gerst <brgerst@gmail.com>, Josh Poimboeuf <jpoimboe@redhat.com>, Denys Vlasenko <dvlasenk@redhat.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Juergen Gross <jgross@suse.com>, David Laight <David.Laight@aculab.com>, Eduardo Valentin <eduval@amazon.com>, "Liguori, Anthony" <aliguori@amazon.com>, Will Deacon <will.deacon@arm.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Dan Williams <dan.j.williams@intel.com>

On Thu, Dec 14, 2017 at 3:27 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> From: Thomas Gleixner <tglx@linutronix.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.

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