Re: [PATCH] x86/boot/KASLR: Extend movable_node option for KASLR

[Dou Liyang <douly.fnst@cn.fujitsu.com>]

Hi chao

At 08/04/2017 10:01 AM, Chao Fan wrote:
> On Fri, Aug 04, 2017 at 09:37:14AM +0800, Dou Liyang wrote:
>> Hi Chao,Baoquan
>>
>> At 08/04/2017 07:49 AM, Baoquan He wrote:
>>> On 08/03/17 at 08:24pm, Chao Fan wrote:
>>>> It's almost another "mem=".
>>>
>>
>> No, it is different.
>>
>> See Documentation/kernel-parameters:
>>
>> "mem=" will force usage of a specific amount of memory and kernel will
>> not see the whole system memory.
>>
>> But "movable_node=" will not do that.
>>
>>
>>> Then why not using 'mem=' directly?
>>>
>>
>> Before answer this question, let's first discuss why the users want to
>> replace "mem=" with "movable_node" when they hope to support NUMA node
>> hot-plug.
>>
>> I guess the real reason is that:
>>
>> When booting up the system, We should have the whole memory not just
>> the un-hotpluggable memory which restrict by "mem=", eg:
>>
>> we boot up kernel with 4 node:
>>
>> node 0 size: 1024 MB  immovable
>> node 1 size: 1024 MB  movable
>> node 2 size: 1024 MB  movable
>> node 3 size: 1024 MB  movable
>>
>> If we use "mem=1024M" in the command line, we just can use 1G memory.
>> But actually, we should have 4G normally.
>>
>> Above is also one reason for why not using 'mem=' directly. Following
>> is other reasons:
>>
> Hi Dou,
>
>> 1). each kernel option has its own role, we'd better misuse them.
>
> I guess you mean "we'd better not misuse them"
>

Oops, yes, thanks!

>> 2). movable_node is used as a boot-time switch to make nodes movable
>> or not, it should consider any situations, such as KASLR.
>
> Yes, then in my understanding, as for this issue, you will leave both
> "movable_node" and "movable_node=nn[KMG]" in kernel option, right?

Yes, Both.

> If so, then what will happen when only "movable_node" specified
> without "movable_node=nn[KMG]"?

If the system does not support KASLR and has movable node, people can
use movable_node directly or use movable_node=nn[KMG], but the
parameter "nn" will useless.

If the system supports both KASLR and movable node, please use
movable_node=nn[KMG] instead of movable_node.

Thanks,
	dou.

> If I misunderstand it, please let me know.
>
> Thanks,
> Chao Fan
>
>>
>>
>> Thanks,
>> 	dou.
>>
>>>>
>>>> On Thu, Aug 03, 2017 at 08:17:21PM +0800, Dou Liyang wrote:
>>>>> movable_node is a boot-time switch to make hot-pluggable memory
>>>>> NUMA nodes to be movable. This option is based on an assumption
>>>>> that any node which the kernel resides in is defined as
>>>>> un-hotpluggable. Linux can allocates memory near the kernel image
>>>>> to try the best to keep the kernel away from hotpluggable memory
>>>>> in the same NUMA node. So other nodes can be movable.
>>>>>
>>>>> But, KASLR doesn't know which node is un-hotpluggable, the all
>>>>> hotpluggable memory ranges is recorded in ACPI SRAT table, SRAT
>>>>> is not parsed. So, KASLR may randomize the kernel in a movable
>>>>> node which will be immovable.
>>>>>
>>>>> Extend movable_node option to restrict kernel to be randomized in
>>>>> immovable nodes by adding a parameter. this parameter sets up
>>>>> the boundaries between the movable nodes and immovable nodes.
>>>>>
>>>>> Reported-by: Chao Fan <fanc.fnst@cn.fujitsu.com>
>>>>> Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
>>>>> ---
>>>>> Documentation/admin-guide/kernel-parameters.txt | 11 +++++++++--
>>>>> arch/x86/boot/compressed/kaslr.c                | 19 ++++++++++++++++---
>>>>> 2 files changed, 25 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>>>> index d9c171c..44c7e33 100644
>>>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>>>> @@ -2305,7 +2305,8 @@
>>>>> 	mousedev.yres=	[MOUSE] Vertical screen resolution, used for devices
>>>>> 			reporting absolute coordinates, such as tablets
>>>>>
>>>>> -	movablecore=nn[KMG]	[KNL,X86,IA-64,PPC] This parameter
>>>>> +	movablecore=nn[KMG]
>>>>> +			[KNL,X86,IA-64,PPC] This parameter
>>>>> 			is similar to kernelcore except it specifies the
>>>>> 			amount of memory used for migratable allocations.
>>>>> 			If both kernelcore and movablecore is specified,
>>>>> @@ -2315,12 +2316,18 @@
>>>>> 			that the amount of memory usable for all allocations
>>>>> 			is not too small.
>>>>>
>>>>> -	movable_node	[KNL] Boot-time switch to make hotplugable memory
>>>>> +	movable_node	[KNL] Boot-time switch to make hot-pluggable memory
>>>>> 			NUMA nodes to be movable. This means that the memory
>>>>> 			of such nodes will be usable only for movable
>>>>> 			allocations which rules out almost all kernel
>>>>> 			allocations. Use with caution!
>>>>>
>>>>> +	movable_node=nn[KMG]
>>>>> +			[KNL] Extend movable_node to work well with KASLR. This
>>>>> +			parameter is the boundaries between the movable nodes
>>>>> +			and immovable nodes, the memory which exceeds it will
>>>>> +			be regarded as hot-pluggable.
>>>>> +
>>>>> 	MTD_Partition=	[MTD]
>>>>> 			Format: <name>,<region-number>,<size>,<offset>
>>>>>
>>>>> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
>>>>> index 91f27ab..7e2351b 100644
>>>>> --- a/arch/x86/boot/compressed/kaslr.c
>>>>> +++ b/arch/x86/boot/compressed/kaslr.c
>>>>> @@ -89,7 +89,10 @@ struct mem_vector {
>>>>> static bool memmap_too_large;
>>>>>
>>>>>
>>>>> -/* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
>>>>> +/*
>>>>> + * Store memory limit specified by the following situations:
>>>>> + * "mem=nn[KMG]" or "memmap=nn[KMG]" or "movable_node=nn[KMG]"
>>>>> + */
>>>>> unsigned long long mem_limit = ULLONG_MAX;
>>>>>
>>>>>
>>>>> @@ -212,7 +215,8 @@ static int handle_mem_memmap(void)
>>>>> 	char *param, *val;
>>>>> 	u64 mem_size;
>>>>>
>>>>> -	if (!strstr(args, "memmap=") && !strstr(args, "mem="))
>>>>> +	if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
>>>>> +		!strstr(args, "movable_node="))
>>>>> 		return 0;
>>>>>
>>>>> 	tmp_cmdline = malloc(len + 1);
>>>>> @@ -247,7 +251,16 @@ static int handle_mem_memmap(void)
>>>>> 				free(tmp_cmdline);
>>>>> 				return -EINVAL;
>>>>> 			}
>>>>> -			mem_limit = mem_size;
>>>>> +			mem_limit = mem_limit > mem_size ? mem_size : mem_limit;
>>>>> +		} else if (!strcmp(param, "movable_node")) {
>>>>> +			char *p = val;
>>>>> +
>>>>> +			mem_size = memparse(p, &p);
>>>>> +			if (mem_size == 0) {
>>>>> +				free(tmp_cmdline);
>>>>> +				return -EINVAL;
>>>>> +			}
>>>>> +			mem_limit = mem_limit > mem_size ? mem_size : mem_limit;
>>>>> 		}
>>>>> 	}
>>>>>
>>>>> --
>>>>> 2.5.5
>>>>>
>>>>
>>>>
>>>
>>>
>>>
>