linux-kernel - Re: [PATCH v2 0/4] Make IA32_EMULATION boot time overridable

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Message-ID: <95a3bf1b-96cf-5341-e3e1-828fd4210ce1@suse.com>
Date:   Sun, 11 Jun 2023 11:19:19 +0300
From:   Nikolay Borisov <nik.borisov@...e.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "x86@...nel.org" <x86@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "jslaby@...e.cz" <jslaby@...e.cz>
Subject: Re: [PATCH v2 0/4] Make IA32_EMULATION boot time overridable



On 11.06.23 г. 0:46 ч., David Laight wrote:
> From: Nikolay Borisov
>> Sent: 09 June 2023 12:13
>>
>> Here's the 2nd version of the patch which aims to make IA32_EMULATION essentially
>> a boot time option. The changes in this posting are:
> 
> Does it make any sense to be able to enable/disable it at run-time
> (through a sysctl).

I'd say now, because then we are losing consistency, that is if the 
sysctl is off, then some 32bit process is being run, then you flip it 
back to on and suddenly this process dies (if it's using syscalls that is).

With a boot time switch we'll ensure that no 32bit process can be 
loaded, which at least can give the sysadmin some assurance that the 
machine is 32bit clean. Am I missing something?

> Perhaps only if enabled at boot - where it can be a 'soft disable'
> even though the cpu is initialised to allow the 32bit system calls.
> 
> Remember, if you are root (and the system isn't hard locked down)

Well, if you are root then every bet's off?

> it is pretty easy to change a global boolean variable.
> So it doesn't really affect the attack surface.
> 
> 	David
> 
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