linux-kernel - Re: [PATCH v3 36/37] x86/cet/shstk: Add ARCH_CET

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Date:   Tue, 15 Nov 2022 22:21:04 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "bsingharora@...il.com" <bsingharora@...il.com>,
        "hpa@...or.com" <hpa@...or.com>,
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Subject: Re: [PATCH v3 36/37] x86/cet/shstk: Add ARCH_CET_UNLOCK

On Tue, Nov 15, 2022 at 01:00:40PM -0800, Dave Hansen wrote:
> On 11/15/22 12:57, Peter Zijlstra wrote:
> > On Tue, Nov 15, 2022 at 08:01:12PM +0000, Edgecombe, Rick P wrote:
> >>>> +	if (task != current) {
> >>>> +		if (option == ARCH_CET_UNLOCK &&
> >>>> IS_ENABLED(CONFIG_CHECKPOINT_RESTORE)) {
> >>> Why make this conditional on CRIU at all?
> >> Kees asked for it, I think he was worried about attackers using it to
> >> unlock and disable shadow stack. So wanted to lock it down to the
> >> maximum.
> > Well, distros will all have this stuff enabled no? So not much
> > protection in practise.
> 
> Yeah, that's true for the distros.
> 
> But, I would imagine that our more paranoid friends like the ChromeOS
> folks might appreciate this.

ptrace can modify text, I'm not sure what if anything we're protecting
against.