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

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Date:	Wed, 11 May 2016 19:11:57 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Andi Kleen <ak@...ux.intel.com>
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

On Wed, May 11, 2016 at 3:40 PM, Andi Kleen <ak@...ux.intel.com> wrote:
>> 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.

So we should retain this behavior for all of 64-bit?

>> 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?

I just don't have enough context to make sense of it. What two bits?
Always behaved what way?Affected by what?

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security