linux-kernel - Re: [PATCH 0/3] PTI for x86-32 Fixes and Updates

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Date:   Mon, 23 Jul 2018 23:55:57 +0200
From:   Pavel Machek <pavel@....cz>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Peter Anvin <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jürgen Groß <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>,
        "David H . Gutteridge" <dhgutteridge@...patico.ca>,
        Joerg Roedel <jroedel@...e.de>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH 0/3] PTI for x86-32 Fixes and Updates

Hi!

> > What I want is "if A can ptrace B, and B has pti disabled, A can have
> > pti disabled as well". Now.. I see someone may want to have it
> > per-thread, because for stuff like javascript JIT, thread may have
> > rights to call ptrace, but is unable to call ptrace because JIT
> > removed that ability... hmm...
> 
> No, you don’t want that. The problem is that Meltdown isn’t a problem that exists in isolation. It’s very plausible that JavaScript code could trigger a speculation attack that, with PTI off, could read kernel memory.

Yeah, the web browser threads that run javascript code should have PTI
on. But maybe I want the rest of web browser with PTI off.

So... yes, I see why someone may want it per-thread (and not
per-process).

I guess per-process would be good enough for me. Actually, maybe even
per-uid. I don't have any fancy security here, so anything running uid
0 and 1000 is close enough to trusted.

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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