linux-kernel - Re: [PATCH 1/4] mm: add DEBUG

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Message-ID: <CANXhq0rW5j+uAymXbfsND9AXHYvM+fPUX9YYYRVXY-Y1u6yo0Q@mail.gmail.com>
Date:   Mon, 27 Apr 2020 16:47:47 +0800
From:   Zong Li <zong.li@...ive.com>
To:     Will Deacon <will@...nel.org>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, catalin.marinas@....com,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/4] mm: add DEBUG_WX support

On Mon, Apr 27, 2020 at 3:49 PM Will Deacon <will@...nel.org> wrote:
>
> On Tue, Apr 21, 2020 at 04:17:12PM +0800, Zong Li wrote:
> > Some architectures support DEBUG_WX function, it's verbatim from each
> > others. Extract to mm/Kconfig.debug for shared use.
> >
> > Signed-off-by: Zong Li <zong.li@...ive.com>
> > Suggested-by: Palmer Dabbelt <palmer@...belt.com>
> > ---
> >  mm/Kconfig.debug | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> >
> > diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> > index 0271b22e063f..077458ad968d 100644
> > --- a/mm/Kconfig.debug
> > +++ b/mm/Kconfig.debug
> > @@ -118,6 +118,39 @@ config DEBUG_RODATA_TEST
> >      ---help---
> >        This option enables a testcase for the setting rodata read-only.
> >
> > +config ARCH_HAS_DEBUG_WX
> > +     bool
> > +
> > +config DEBUG_WX
> > +     bool "Warn on W+X mappings at boot"
> > +     depends on ARCH_HAS_DEBUG_WX
> > +     select PTDUMP_CORE
> > +     help
> > +       Generate a warning if any W+X mappings are found at boot.
> > +
> > +       This is useful for discovering cases where the kernel is leaving
> > +       W+X mappings after applying NX, as such mappings are a security risk.
> > +       This check also includes UXN, which should be set on all kernel
> > +       mappings.
>
> "UXN" is the name of a bit in the arm64 page-table descriptors, so this
> should be reworded now that it's in generic help text.
>

It's exactly. Sorry for missing the statement.

Hi Andrew,
Shall I send a next version patch to fix it? It should be "This is
useful for discovering cases where the kernel is leaving W+X mappings
after applying NX, as such mappings are a security risk." here.

> Will