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Subject: Re: [PATCH v9 4/8] powerpc/mm/ptdump: debugfs handler for W+X checks
 at runtime
To: Jordan Niethe <jniethe5@gmail.com>, linuxppc-dev@lists.ozlabs.org
References: <20210316031741.1004850-1-jniethe5@gmail.com>
 <20210316031741.1004850-4-jniethe5@gmail.com>
From: Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <6d91193f-1428-67f2-eaaa-59f41859af7c@csgroup.eu>
Date: Tue, 16 Mar 2021 07:47:10 +0100
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Cc: christophe.leroy@c-s.fr, ajd@linux.ibm.com,
 Kees Cook <keescook@chromium.org>, npiggin@gmail.com,
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Le 16/03/2021 à 04:17, Jordan Niethe a écrit :
> From: Russell Currey <ruscur@russell.cc>
> 
> Very rudimentary, just
> 
> 	echo 1 > [debugfs]/check_wx_pages
> 
> and check the kernel log.  Useful for testing strict module RWX.
> 
> Updated the Kconfig entry to reflect this.
> 
> Also fixed a typo.

Why not just perform the test everytime someone dumps kernel_page_tables ?

> 
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Russell Currey <ruscur@russell.cc>
> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> ---
>   arch/powerpc/Kconfig.debug      |  6 ++++--
>   arch/powerpc/mm/ptdump/ptdump.c | 21 ++++++++++++++++++++-
>   2 files changed, 24 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
> index ae084357994e..56e99e9a30d9 100644
> --- a/arch/powerpc/Kconfig.debug
> +++ b/arch/powerpc/Kconfig.debug
> @@ -371,7 +371,7 @@ config PPC_PTDUMP
>   	  If you are unsure, say N.
>   
>   config PPC_DEBUG_WX
> -	bool "Warn on W+X mappings at boot"
> +	bool "Warn on W+X mappings at boot & enable manual checks at runtime"
>   	depends on PPC_PTDUMP && STRICT_KERNEL_RWX
>   	help
>   	  Generate a warning if any W+X mappings are found at boot.
> @@ -385,7 +385,9 @@ config PPC_DEBUG_WX
>   	  of other unfixed kernel bugs easier.
>   
>   	  There is no runtime or memory usage effect of this option
> -	  once the kernel has booted up - it's a one time check.
> +	  once the kernel has booted up, it only automatically checks once.
> +
> +	  Enables the "check_wx_pages" debugfs entry for checking at runtime.
>   
>   	  If in doubt, say "Y".
>   
> diff --git a/arch/powerpc/mm/ptdump/ptdump.c b/arch/powerpc/mm/ptdump/ptdump.c
> index aca354fb670b..78497d57b66b 100644
> --- a/arch/powerpc/mm/ptdump/ptdump.c
> +++ b/arch/powerpc/mm/ptdump/ptdump.c
> @@ -4,7 +4,7 @@
>    *
>    * This traverses the kernel pagetables and dumps the
>    * information about the used sections of memory to
> - * /sys/kernel/debug/kernel_pagetables.
> + * /sys/kernel/debug/kernel_page_tables.
>    *
>    * Derived from the arm64 implementation:
>    * Copyright (c) 2014, The Linux Foundation, Laura Abbott.
> @@ -459,6 +459,25 @@ void ptdump_check_wx(void)
>   	else
>   		pr_info("Checked W+X mappings: passed, no W+X pages found\n");
>   }
> +
> +static int check_wx_debugfs_set(void *data, u64 val)
> +{
> +	if (val != 1ULL)
> +		return -EINVAL;
> +
> +	ptdump_check_wx();
> +
> +	return 0;
> +}
> +
> +DEFINE_SIMPLE_ATTRIBUTE(check_wx_fops, NULL, check_wx_debugfs_set, "%llu\n");
> +
> +static int ptdump_check_wx_init(void)
> +{
> +	return debugfs_create_file("check_wx_pages", 0200, NULL,
> +				   NULL, &check_wx_fops) ? 0 : -ENOMEM;
> +}
> +device_initcall(ptdump_check_wx_init);
>   #endif
>   
>   static int ptdump_init(void)
>