linux-hardening - Re: [PATCH v5 3/8] powerpc/mm/ptdump: debugfs handler for W+X checks at runtime

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Date:   Thu, 7 Apr 2022 07:39:51 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Kees Cook <keescook@...omium.org>,
        Russell Currey <ruscur@...sell.cc>,
        "jniethe5@...il.com" <jniethe5@...il.com>
CC:     "ajd@...ux.ibm.com" <ajd@...ux.ibm.com>,
        "npiggin@...il.com" <npiggin@...il.com>,
        "joel@....id.au" <joel@....id.au>,
        "dja@...ens.net" <dja@...ens.net>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH v5 3/8] powerpc/mm/ptdump: debugfs handler for W+X checks
 at runtime



Le 06/04/2022 à 20:55, Kees Cook a écrit :
> *thread necromancy*
> 
> Is this patch still something folks are working on? It'd be nice to be
> able to trigger this check at runtime.

The series was taken over by Jordan.

v15 of the series was accepted, but that particular patch was dropped in 
v11 (see 
https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20210429031602.2606654-1-jniethe5@gmail.com/)

The comment was:

Some patches were dropped from this revision:
   powerpc/mm/ptdump: debugfs handler for W+X checks at runtime
     - Will use Christophe's generic ptdump series

Not sure what happened after that.

Christophe

> 
> -Kees
> 
> On Wed, Feb 26, 2020 at 05:35:46PM +1100, Russell Currey wrote:
>> 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.
>>
>> 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 0b063830eea8..e37960ef68c6 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 && STRICT_KERNEL_RWX
>>   	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 206156255247..a15e19a3b14e 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.
>> @@ -413,6 +413,25 @@ 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)
>> -- 
>> 2.25.1
>>
>