[PATCH v3 3/4] powerpc/mm/ptdump: debugfs handler for W+X checks at runtime

[Christophe Leroy]

Le 04/10/2019 à 09:50, Russell Currey a écrit :
> Very rudimentary, just
> 
> 	echo 1 > [debugfs]/check_wx_pages
> 
> and check the kernel log.  Useful for testing strict module RWX.
> 
> Also fixed a typo.
> 
> Signed-off-by: Russell Currey <ruscur at russell.cc>
> ---
>   arch/powerpc/mm/ptdump/ptdump.c | 31 +++++++++++++++++++++++++------
>   1 file changed, 25 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/powerpc/mm/ptdump/ptdump.c b/arch/powerpc/mm/ptdump/ptdump.c
> index 2f9ddc29c535..0547cd9f264e 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.
> @@ -409,16 +409,35 @@ 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");
>   #endif
>   
>   static int ptdump_init(void)
>   {
> -	struct dentry *debugfs_file;
> -
>   	populate_markers();
>   	build_pgtable_complete_mask();
> -	debugfs_file = debugfs_create_file("kernel_page_tables", 0400, NULL,
> -			NULL, &ptdump_fops);
> -	return debugfs_file ? 0 : -ENOMEM;
> +
> +	if (!debugfs_create_file("kernel_page_tables", 0400, NULL,
> +				 NULL, &ptdump_fops))
> +		return -ENOMEM;
> +
> +#ifdef CONFIG_PPC_DEBUG_WX
> +	if (!debugfs_create_file("check_wx_pages", 0200, NULL,
> +				 NULL, &check_wx_fops))
> +		return -ENOMEM;
> +#endif

The above seems to be completely independant from everything else in 
ptdump_init().

Could we avoid this #ifdef block inside ptdump_init() by creating a 
selfstanding device_initcall() for that through a function called 
ptdump_check_wx_init() defined inside the same #ifdef block as 
ptdump_check_wx() ?

Christophe

> +
> +	return 0;
>   }
>   device_initcall(ptdump_init);
>