linux-kernel - Re: [RFC PATCH v2 6/6] x86/entry/pti: don't switch PGD on when pti

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Message-ID: <20180112202238.hc2dkjvmu7wlz7xw@gmail.com>
Date:   Fri, 12 Jan 2018 21:22:38 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Willy Tarreau <w@....eu>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [RFC PATCH v2 6/6] x86/entry/pti: don't switch PGD on when
 pti_disable is set


* Andy Lutomirski <luto@...capital.net> wrote:

> > Oh, and yes, I think the npti flag should also break ptrace(). I do agree with 
> > Andy that it's a "capability", although I do not think it should actually be 
> > implemented as one.
> 
> For all that Linux capabilities are crap, nopti walks like one and quacks like 
> one.  It needs to affect ptrace() permissions, it needs a way to disable it 
> systemwide, it needs LSM integration, etc.  Using CAP_DISABLE_PTI gives us all 
> of this without tons of churn, auditing, and a whole new configuration thingy 
> for each LSM.  And I avoids permanently polluting ptrace checks, the LSM 
> interface, etc for what is, essentially, a performance hack to work around a 
> blatant error in the design of some CPUs.
> 
> Plus, with ambient caps, we already did the nasty part of the with and finished 
> all the relevant bikeshedding.
> 
> So I'd rather just hold my nose and add the new capability bit.

Those all seem pretty valid arguments to me.

Thanks,

	Ingo