Re: [kernel-hardening] [RFC 2/7] init: add set_ro_mostly_after_init_rw/ro function

[Ho-Eun Ryu]

> On 20 Feb 2017, at 7:22 PM, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> 
> On Sun, Feb 19, 2017 at 07:04:05PM +0900, Hoeun Ryu wrote:
>> Add set_ro_mostly_after_init_rw/ro pair to modify memory attributes for
>> memory marked as `ro_mostly_after_init`.
>> 
>> I am doubtful that this is the right place where these functions reside and
>> these functions are suitable for all architectures for memory attributes
>> modification. Please comment.
> 
> These won't work for arm64, since set_memory_* only work on
> page-granular mappings in the vmalloc area.
> 
> The "real" kernel mappings can use larger block mappings, and would need
> to be split (which cannot be done at runtime) before permissions could
> be changed at page granularity.

So I sent RFC 6/7 [1] and 7/7 [2] that splits the block mapping to the page granular.
I think you and Ard Biesheuvel donât like it anyway.

[1] : https://lkml.org/lkml/2017/2/19/38
[2] : https://lkml.org/lkml/2017/2/19/39

> 
> Thanks,
> Mark.
> 
>> Signed-off-by: Hoeun Ryu <hoeun.ryu@xxxxxxxxx>
>> ---
>> include/linux/init.h |  6 ++++++
>> init/main.c          | 24 ++++++++++++++++++++++++
>> 2 files changed, 30 insertions(+)
>> 
>> diff --git a/include/linux/init.h b/include/linux/init.h
>> index 79af096..d68e4f7 100644
>> --- a/include/linux/init.h
>> +++ b/include/linux/init.h
>> @@ -131,6 +131,12 @@ extern bool rodata_enabled;
>> #endif
>> #ifdef CONFIG_STRICT_KERNEL_RWX
>> void mark_rodata_ro(void);
>> +
>> +void set_ro_mostly_after_init_rw(void);
>> +void set_ro_mostly_after_init_ro(void);
>> +#else
>> +static inline void set_ro_mostly_after_init_rw(void) { }
>> +static inline void set_ro_mostly_after_init_ro(void) { }
>> #endif
>> 
>> extern void (*late_time_init)(void);
>> diff --git a/init/main.c b/init/main.c
>> index 4719abf..a5d4873 100644
>> --- a/init/main.c
>> +++ b/init/main.c
>> @@ -941,6 +941,30 @@ static void mark_readonly(void)
>> 	} else
>> 		pr_info("Kernel memory protection disabled.\n");
>> }
>> +
>> +void set_ro_mostly_after_init_rw(void)
>> +{
>> +	unsigned long start = PFN_ALIGN(__start_data_ro_mostly_after_init);
>> +	unsigned long end = PFN_ALIGN(&__end_data_ro_mostly_after_init);
>> +	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
>> +
>> +	if (!rodata_enabled)
>> +		return;
>> +
>> +	set_memory_rw(start, nr_pages);
>> +}
>> +
>> +void set_ro_mostly_after_init_ro(void)
>> +{
>> +	unsigned long start = PFN_ALIGN(__start_data_ro_mostly_after_init);
>> +	unsigned long end = PFN_ALIGN(&__end_data_ro_mostly_after_init);
>> +	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
>> +
>> +	if (!rodata_enabled)
>> +		return;
>> +
>> +	set_memory_ro(start, nr_pages);
>> +}
>> #else
>> static inline void mark_readonly(void)
>> {
>> -- 
>> 2.7.4
>>