linux-kernel - Re: [PATCH v2 17/18] arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT

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Date:   Tue, 12 Dec 2017 10:28:27 +0000
From:   Will Deacon <will.deacon@....com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Mark Salter <msalter@...hat.com>,
        Laura Abbott <labbott@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 17/18] arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0

On Tue, Dec 12, 2017 at 09:44:09AM +0100, Geert Uytterhoeven wrote:
> Hi Will,
> 
> On Thu, Nov 30, 2017 at 5:39 PM, Will Deacon <will.deacon@....com> wrote:
> > Add a Kconfig entry to control use of the entry trampoline, which allows
> > us to unmap the kernel whilst running in userspace and improve the
> > robustness of KASLR.
> >
> > Signed-off-by: Will Deacon <will.deacon@....com>
> 
> This is now commit 084eb77cd3a81134 in arm64/for-next/core.
> 
> > ---
> >  arch/arm64/Kconfig | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index fdcc7b9bb15d..3af1657fcac3 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -833,6 +833,19 @@ config FORCE_MAX_ZONEORDER
> >           However for 4K, we choose a higher default value, 11 as opposed to 10, giving us
> >           4M allocations matching the default size used by generic code.
> >
> > +config UNMAP_KERNEL_AT_EL0
> > +       bool "Unmap kernel when running in userspace (aka \"KAISER\")"
> 
> But I believe this is no longer called KAISER?

That's right, but KAISER is the original name in the paper and so I figured
it was worth mentioning just here to help people identify what this feature
is. The command line option is "kpti" to align with x86.

Will