Re: [PATCH] livepatch: x86: bugfix about kASLR

[zhouchengming <zhouchengming1@huawei.com>]

On 2015/11/4 17:44, Jiri Kosina wrote:
> On Wed, 4 Nov 2015, Zhou Chengming wrote:
>
>> When enable KASLR, func->old_addr will be set to zero
>> and livepatch will find the right old address.
>> But for reloc, livepatch just verify it using reloc->val
>> (old addr from user), so verify failed and report
>> "kernel mismatch" error.
>>
>> Reported-by: Cyril B.<cbay@alwaysdata.com>
>> Signed-off-by: Zhou Chengming<zhouchengming1@huawei.com>
>> ---
>>   kernel/livepatch/core.c |    7 ++++++-
>>   1 files changed, 6 insertions(+), 1 deletions(-)
>>
>> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
>> index 53196e2..c8885c6 100644
>> --- a/kernel/livepatch/core.c
>> +++ b/kernel/livepatch/core.c
>> @@ -311,7 +311,12 @@ static int klp_write_object_relocations(struct module *pmod,
>>   		return -EINVAL;
>>
>>   	for (reloc = obj->relocs; reloc->name; reloc++) {
>> -		if (!klp_is_module(obj)) {
>> +
>> +#if defined(CONFIG_RANDOMIZE_BASE)
> CONFIG_RANDOMIZE_BASE being enabled by itself doesn't directly imply that
> kASLR has been actually really enabled during runtime. You need
> to check kaslr_enabled() as well.

Right.

>> +		/* KASLR is enabled, disregard old_addr from user */
>> +		reloc->val = 0;
> Is there a reason why to discard it completely? Adding kaslr_offset()
> should give us the correct address, right?
>
> Thanks,
>

Yes, it's definitely better.

Thanks