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

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Message-ID: <20200427074915.GA11787@willie-the-truck>
Date:   Mon, 27 Apr 2020 08:49:16 +0100
From:   Will Deacon <will@...nel.org>
To:     Zong Li <zong.li@...ive.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, paul.walmsley@...ive.com,
        palmer@...belt.com, 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@...ts.infradead.org
Subject: Re: [PATCH 1/4] mm: add DEBUG_WX support

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.

Will