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Date: Tue, 31 Dec 2019 18:14:13 +0100
From: Christophe Leroy <christophe.leroy@....fr>
To: Russell Currey <ruscur@...sell.cc>
Cc: kernel-hardening@...ts.openwall.com, npiggin@...il.com, dja@...ens.net,
 ajd@...ux.ibm.com, mpe@...erman.id.au, joel@....id.au,
 linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v6 3/5] powerpc/mm/ptdump: debugfs handler for W+X
 checks at runtime

Russell Currey <ruscur@...sell.cc> a écrit :

> Very rudimentary, just
>
> 	echo 1 > [debugfs]/check_wx_pages
>
> and check the kernel log.  Useful for testing strict module RWX.

For testing strict module RWX you could instead implement  
module_arch_freeing_init() and call  ptdump_check_wx() from there.

Christophe

>
> Updated the Kconfig entry to reflect this.
>
> Also fixed a typo.
>
> Signed-off-by: Russell Currey <ruscur@...sell.cc>
> ---
>  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 4e1d39847462..7c14c9728bc0 100644
> --- a/arch/powerpc/Kconfig.debug
> +++ b/arch/powerpc/Kconfig.debug
> @@ -370,7 +370,7 @@ 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
>  	help
>  	  Generate a warning if any W+X mappings are found at boot.
> @@ -384,7 +384,9 @@ 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 2f9ddc29c535..b6cba29ae4a0 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.
> @@ -409,6 +409,25 @@ 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)
> --
> 2.24.1


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