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

From: Dou Liyang
Date: Thu Aug 03 2017 - 21:37:39 EST

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

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:

1). each kernel option has its own role, we'd better 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.


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)
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;