linux-kernel - Re: [RFC PATCH v2 2/6] x86/arch_prctl: add ARCH_GET_NOPTI and ARCH_SET

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Message-ID: <20180109145157.5ltqbz4o5sqkcggb@pd.tnic>
Date:   Tue, 9 Jan 2018 15:51:57 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Willy Tarreau <w@....eu>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>
Subject: Re: [RFC PATCH v2 2/6] x86/arch_prctl: add ARCH_GET_NOPTI and
 ARCH_SET_NOPTI to enable/disable PTI

On Tue, Jan 09, 2018 at 03:36:53PM +0100, Willy Tarreau wrote:
> I see and am not particularly against this, but what use case do you
> have in mind precisely ? I doubt it's just saving a few tens of bytes,
> so probably you're more concerned about the potential risks this opens ?
> But given we only allow this for CAP_SYS_RAWIO and these ones already
> have access to /dev/mem and many other things, don't you think there
> are much easier ways to dump kernel memory in this case than trying to
> inject some meltdown code into the victim process ? Or maybe you have
> other cases in mind that I'm not seeing.

I'd like this to be config-controllable so that distros can make the
decision whether/if they want to support the whole per-mm thing.

Also, if CAP_SYS_RAWIO is going to protect, please make the
ARCH_GET_NOPTI variant check it too.

Thx.

-- 
Regards/Gruss,
    Boris.

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