linux-kernel - Re: [PATCH] x86_64: Disabling read-implies-exec when the stack is executable

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Date:	Wed, 11 May 2016 15:40:58 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Hector Marco-Gisbert <hecmargi@....es>,
	Andy Lutomirski <luto@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>, Brian Gerst <brgerst@...il.com>,
	Borislav Petkov <bp@...e.de>,
	Huaitong Han <huaitong.han@...el.com>,
	Ismael Ripoll Ripoll <iripoll@....es>
Subject: Re: [PATCH] x86_64: Disabling read-implies-exec when the stack is
 executable

> However, I would tend to agree: RIE should only be needed on 32-bit
> since 64-bit started its life knowing about no-exec permissions.

NX was not in the original AMD K8 chips.  Was only added some time later.

> set_personality_64bit()'s (which is confusingly just an initializer
> and not called during the personality() syscall) comment about this
> makes no sense to me:
> 
>         /* TBD: overwrites user setup. Should have two bits.
>            But 64bit processes have always behaved this way,
>            so it's not too bad. The main problem is just that
>            32bit childs are affected again. */
>         current->personality &= ~READ_IMPLIES_EXEC;

What does not make sense?

-Andi