linux-kernel - Re: [PATCH 28/37] x86/mm/pti: Map kernel-text to user-space on 32 bit kernels

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Message-ID: <20180423174850.zjpx2mcs6dtfkgl3@suse.de>
Date:   Mon, 23 Apr 2018 19:48:50 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Kees Cook <keescook@...gle.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen 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 KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        Anthony Liguori <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        "David H . Gutteridge" <dhgutteridge@...patico.ca>
Subject: Re: [PATCH 28/37] x86/mm/pti: Map kernel-text to user-space on 32
 bit kernels

On Mon, Apr 23, 2018 at 10:09:19AM -0700, Kees Cook wrote:
> On Mon, Apr 23, 2018 at 8:47 AM, Joerg Roedel <joro@...tes.org> wrote:
> > From: Joerg Roedel <jroedel@...e.de>
> >
> > Keeping the kernel text mapped with G bit set keeps its
> > entries in the TLB across kernel entry/exit and improved the
> > performance. The 64 bit x86 kernels already do this when
> > there is no PCID, so do this in 32 bit as well since PCID is
> > not even supported there.
> 
> I think this should keep at least part of the logic as 64-bit since
> there are other reasons to turn off the Global flag:
> 
> https://lkml.kernel.org/r/20180420222026.D0B4AAC9@viggo.jf.intel.com

That patch you linked is for function pti_kernel_image_global_ok() which
is used on 32 bit too. So any logic implemented for 64 bit to turn off
the global bit will automatically be used on 32 bit.


Regards,

	Joerg