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

[Chao Fan]

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"

>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?
If so, then what will happen when only "movable_node" specified
without "movable_node=nn[KMG]"?
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@xxxxxxxxxxxxxx>
>> > > Signed-off-by: Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>
>> > > ---
>> > > 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
>> > > 
>> > 
>> > 
>> 
>> 
>>