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Date: Fri, 8 Dec 2017 22:49:45 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
cc: Andy Lutomirski <luto@kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
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        David Laight <David.Laight@aculab.com>,
        Kees Cook <keescook@chromium.org>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: x86/ldt: Prevent ldt inheritance on exec
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On Fri, 8 Dec 2017, Linus Torvalds wrote:

> On Fri, Dec 8, 2017 at 12:02 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> > 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.
> 
> Looks sane. That said, can't we separate this out into the copy_mm()
> phase only?
> 
> We have "arch_dup_mmap()" that is called on fork() only, so that could
> do the LDT copy from the old mm, and the actual init_new_context would
> just zero it out.
> 
> Then there wouldn't be any odd "check if this is an execve" because
> the copying would be done in the right place.

Yes, that should work. It just needs to change arch_dup_mmap() so it can
return an error code.

Thanks,

	tglx